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path: root/src/libnsbmp.c
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/*
 * Copyright 2006 Richard Wilson <richard.wilson@netsurf-browser.org>
 * Copyright 2008 Sean Fox <dyntryx@gmail.com>
 *
 * This file is part of NetSurf's libnsbmp, http://www.netsurf-browser.org/
 * Licenced under the MIT License,
 *                http://www.opensource.org/licenses/mit-license.php
 */

/**
 * \file
 * BMP decoding implementation
 *
 * This library decode windows bitmaps and icons from their disc images.
 *
 * The image format is described in several documents:
 *  https://msdn.microsoft.com/en-us/library/dd183391(v=vs.85).aspx
 *  http://www.fileformat.info/format/bmp/egff.htm
 *  https://en.wikipedia.org/wiki/BMP_file_format
 *
 * Despite the format being clearly defined many bitmaps found on the web are
 *  not compliant and this implementation attempts to cope with as many issues
 *  as possible rather than simply failing.
 */

#include <assert.h>
#include <stdbool.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <stdint.h>

#include <libnsbmp.h>

#include "utils/log.h"

/* squashes unused variable compiler warnings */
#define UNUSED(x) ((x)=(x))

/* BMP flags */
#define BMP_FILE_HEADER_SIZE 14
#define ICO_FILE_HEADER_SIZE 6
#define ICO_DIR_ENTRY_SIZE 16

#ifdef WE_NEED_INT8_READING_NOW
static inline int8_t read_int8(uint8_t *data, unsigned int o) {
        return (int8_t) data[o];
}
#endif

static inline uint8_t read_uint8(uint8_t *data, unsigned int o) {
        return (uint8_t) data[o];
}

static inline int16_t read_int16(uint8_t *data, unsigned int o) {
        return (int16_t) (data[o] | (data[o+1] << 8));
}

static inline uint16_t read_uint16(uint8_t *data, unsigned int o) {
        return (uint16_t) (data[o] | (data[o+1] << 8));
}

static inline int32_t read_int32(uint8_t *data, unsigned int o) {
        return (int32_t) (data[o] | (data[o+1] << 8) | (data[o+2] << 16) | (data[o+3] << 24));
}

static inline uint32_t read_uint32(uint8_t *data, unsigned int o) {
        return (uint32_t) (data[o] | (data[o+1] << 8) | (data[o+2] << 16) | (data[o+3] << 24));
}


/**
 * Parse the bitmap info header
 */
static bmp_result bmp_info_header_parse(bmp_image *bmp, uint8_t *data)
{
        uint32_t header_size;
        uint32_t i;
        uint8_t j;
        int32_t width, height;
        uint8_t palette_size;
        unsigned int flags = 0;

        /* a variety of different bitmap headers can follow, depending
         * on the BMP variant. A full description of the various headers
         * can be found at
         * http://msdn.microsoft.com/en-us/library/ms532301(VS.85).aspx
         */
        header_size = read_uint32(data, 0);
        if (bmp->buffer_size < (14 + header_size))
                return BMP_INSUFFICIENT_DATA;
        if (header_size == 12) {
                /* the following header is for os/2 and windows 2.x and consists of:
                 *
                 *	+0	UINT32	size of this header (in bytes)
                 *	+4	INT16	image width (in pixels)
                 *	+6	INT16	image height (in pixels)
                 *	+8	UINT16	number of colour planes (always 1)
                 *	+10	UINT16	number of bits per pixel
                 */
                width = read_int16(data, 4);
                height = read_int16(data, 6);
                if ((width <= 0) || (height == 0))
                        return BMP_DATA_ERROR;
                if (height < 0) {
                        bmp->reversed = true;
                        height = -height;
                }
                /* ICOs only support 256*256 resolutions
                 * In the case of the ICO header, the height is actually the added
                 * height of XOR-Bitmap and AND-Bitmap (double the visible height)
                 * Technically we could remove this check and ICOs with bitmaps
                 * of any size could be processed; this is to conform to the spec.
                 */
                if (bmp->ico) {
                        if ((width > 256) || (height > 512)) {
                                return BMP_DATA_ERROR;
                        } else {
                                bmp->width = width;
                                bmp->height = height / 2;
                        }
                } else {
                        bmp->width = width;
                        bmp->height = height;
                }
                if (read_uint16(data, 8) != 1)
                        return BMP_DATA_ERROR;
                bmp->bpp = read_uint16(data, 10);
                /**
                 * The bpp value should be in the range 1-32, but the only
                 * values considered legal are:
                 * RGB ENCODING: 1, 4, 8, 16, 24 and 32
                 */
                if ((bmp->bpp != 1) && (bmp->bpp != 4) &&
                    (bmp->bpp != 8) &&
                    (bmp->bpp != 16) &&
                    (bmp->bpp != 24) &&
                    (bmp->bpp != 32))
                        return BMP_DATA_ERROR;
                bmp->colours = (1 << bmp->bpp);
                palette_size = 3;
        } else if (header_size < 40) {
                return BMP_DATA_ERROR;
        } else {
                /* the following header is for windows 3.x and onwards. it is a
                 * minimum of 40 bytes and (as of Windows 95) a maximum of 108 bytes.
                 *
                 *	+0	UINT32	size of this header (in bytes)
                 *	+4	INT32	image width (in pixels)
                 *	+8	INT32	image height (in pixels)
                 *	+12	UINT16	number of colour planes (always 1)
                 *	+14	UINT16	number of bits per pixel
                 *	+16	UINT32	compression methods used
                 *	+20	UINT32	size of bitmap (in bytes)
                 *	+24	UINT32	horizontal resolution (in pixels per meter)
                 *	+28	UINT32	vertical resolution (in pixels per meter)
                 *	+32	UINT32	number of colours in the image
                 *	+36	UINT32	number of important colours
                 *	+40	UINT32	mask identifying bits of red component
                 *	+44	UINT32	mask identifying bits of green component
                 *	+48	UINT32	mask identifying bits of blue component
                 *	+52	UINT32	mask identifying bits of alpha component
                 *	+56	UINT32	color space type
                 *	+60	UINT32	x coordinate of red endpoint
                 *	+64	UINT32	y coordinate of red endpoint
                 *	+68	UINT32	z coordinate of red endpoint
                 *	+72	UINT32	x coordinate of green endpoint
                 *	+76	UINT32	y coordinate of green endpoint
                 *	+80	UINT32	z coordinate of green endpoint
                 *	+84	UINT32	x coordinate of blue endpoint
                 *	+88	UINT32	y coordinate of blue endpoint
                 *	+92	UINT32	z coordinate of blue endpoint
                 *	+96	UINT32	gamma red coordinate scale value
                 *	+100	UINT32	gamma green coordinate scale value
                 *	+104	UINT32	gamma blue coordinate scale value
                 */
                width = read_int32(data, 4);
                height = read_int32(data, 8);
                if ((width <= 0) || (height == 0))
                        return BMP_DATA_ERROR;
                if (height < 0) {
                        bmp->reversed = true;
                        height = -height;
                }
                /* ICOs only support 256*256 resolutions
                 * In the case of the ICO header, the height is actually the added
                 * height of XOR-Bitmap and AND-Bitmap (double the visible height)
                 * Technically we could remove this check and ICOs with bitmaps
                 * of any size could be processed; this is to conform to the spec.
                 */
                if (bmp->ico) {
                        if ((width > 256) || (height > 512)) {
                                return BMP_DATA_ERROR;
                        } else {
                                bmp->width = width;
                                bmp->height = height / 2;
                        }
                } else {
                        bmp->width = width;
                        bmp->height = height;
                }
                if (read_uint16(data, 12) != 1)
                        return BMP_DATA_ERROR;
                bmp->bpp = read_uint16(data, 14);
                if (bmp->bpp == 0)
                        bmp->bpp = 8;
                bmp->encoding = read_uint32(data, 16);
                /**
                 * The bpp value should be in the range 1-32, but the only
                 * values considered legal are:
                 * RGB ENCODING: 1, 4, 8, 16, 24 and 32
                 * RLE4 ENCODING: 4
                 * RLE8 ENCODING: 8
                 * BITFIELD ENCODING: 16 and 32
                 */
                switch (bmp->encoding) {
                case BMP_ENCODING_RGB:
                        if ((bmp->bpp != 1) && (bmp->bpp != 4) &&
                            (bmp->bpp != 8) &&
                            (bmp->bpp != 16) &&
                            (bmp->bpp != 24) &&
                            (bmp->bpp != 32))
                                return BMP_DATA_ERROR;
                        break;
                case BMP_ENCODING_RLE8:
                        if (bmp->bpp != 8)
                                return BMP_DATA_ERROR;
                        break;
                case BMP_ENCODING_RLE4:
                        if (bmp->bpp != 4)
                                return BMP_DATA_ERROR;
                        break;
                case BMP_ENCODING_BITFIELDS:
                        if ((bmp->bpp != 16) && (bmp->bpp != 32))
                                return BMP_DATA_ERROR;
                        break;
                        /* invalid encoding */
                default:
                        return BMP_DATA_ERROR;
                        break;
                }
                /* Bitfield encoding means we have red, green, blue, and alpha masks.
                 * Here we acquire the masks and determine the required bit shift to
                 * align them in our 24-bit color 8-bit alpha format.
                 */
                if (bmp->encoding == BMP_ENCODING_BITFIELDS) {
                        if (header_size == 40) {
                                header_size += 12;
                                if (bmp->buffer_size < (14 + header_size))
                                        return BMP_INSUFFICIENT_DATA;
                                for (i = 0; i < 3; i++)
                                        bmp->mask[i] = read_uint32(data, 40 + (i << 2));
                        } else {
                                for (i = 0; i < 4; i++)
                                        bmp->mask[i] = read_uint32(data, 40 + (i << 2));
                        }
                        for (i = 0; i < 4; i++) {
                                if (bmp->mask[i] == 0)
                                        break;
                                for (j = 31; j > 0; j--)
                                        if (bmp->mask[i] & (1 << j)) {
                                                if ((j - 7) > 0)
                                                        bmp->mask[i] &= 0xff << (j - 7);
                                                else
                                                        bmp->mask[i] &= 0xff >> (-(j - 7));
                                                bmp->shift[i] = (i << 3) - (j - 7);
                                                break;
                                        }
                        }
                }
                bmp->colours = read_uint32(data, 32);
                if (bmp->colours == 0)
                        bmp->colours = (1 << bmp->bpp);
                palette_size = 4;
        }
        data += header_size;

        /* if there's no alpha mask, flag the bmp opaque */
        if ((!bmp->ico) && (bmp->mask[3] == 0)) {
                flags |= BMP_OPAQUE;
                bmp->opaque = true;
        }

        /* we only have a palette for <16bpp */
        if (bmp->bpp < 16) {
                /* we now have a series of palette entries of the format:
                 *
                 *	+0	BYTE	blue
                 *	+1	BYTE	green
                 *	+2	BYTE	red
                 *
                 * if the palette is from an OS/2 or Win2.x file then the entries
                 * are padded with an extra byte.
                 */

                /* boundary checking */
                if (bmp->buffer_size < (14 + header_size + ((uint64_t)4 * bmp->colours)))
                        return BMP_INSUFFICIENT_DATA;

                /* create the colour table */
                bmp->colour_table = (uint32_t *)malloc(bmp->colours * 4);
                if (!bmp->colour_table)
                        return BMP_INSUFFICIENT_MEMORY;
                for (i = 0; i < bmp->colours; i++) {
                        bmp->colour_table[i] = data[2] | (data[1] << 8) | (data[0] << 16);
                        if (bmp->opaque)
                                bmp->colour_table[i] |= (0xff << 24);
                        data += palette_size;
                        bmp->colour_table[i] = read_uint32((uint8_t *)&bmp->colour_table[i],0);
                }

                /* some bitmaps have a bad offset if there is a pallete, work
                 * round this by fixing up the data offset to after the palette
                 * but only if there is data following the palette as some
                 * bitmaps encode data in the palette!
                 */
                if ((bmp->bitmap_offset < (uint32_t)(data - bmp->bmp_data)) &&
                    ((bmp->buffer_size - (data - bmp->bmp_data)) > 0)) {
                        bmp->bitmap_offset = data - bmp->bmp_data;
                }
        }

        /* create our bitmap */
        flags |= BMP_NEW | BMP_CLEAR_MEMORY;
        bmp->bitmap = bmp->bitmap_callbacks.bitmap_create(bmp->width, bmp->height, flags);
        if (!bmp->bitmap) {
                if (bmp->colour_table)
                        free(bmp->colour_table);
                bmp->colour_table = NULL;
                return BMP_INSUFFICIENT_MEMORY;
        }
        /* BMPs within ICOs don't have BMP file headers, so the image data should
         * always be right after the colour table.
         */
        if (bmp->ico)
                bmp->bitmap_offset = (intptr_t)data - (intptr_t)bmp->bmp_data;
        return BMP_OK;
}


/**
 * Parse the bitmap file header
 *
 * \param bmp The bitmap.
 * \param data The data for the file header
 * \return BMP_OK on success or error code on faliure
 */
static bmp_result bmp_file_header_parse(bmp_image *bmp, uint8_t *data)
{
        /* standard 14-byte BMP file header is:
         *
         *   +0    UINT16   File Type ('BM')
         *   +2    UINT32   Size of File (in bytes)
         *   +6    INT16    Reserved Field (1)
         *   +8    INT16    Reserved Field (2)
         *   +10   UINT32   Starting Position of Image Data (offset in bytes)
         */
        if (bmp->buffer_size < BMP_FILE_HEADER_SIZE)
                return BMP_INSUFFICIENT_DATA;

        if ((data[0] != (uint8_t)'B') || (data[1] != (uint8_t)'M'))
                return BMP_DATA_ERROR;

        bmp->bitmap_offset = read_uint32(data, 10);

        /* check the offset to data lies within the file */
        if (bmp->bitmap_offset >= bmp->buffer_size) {
                return BMP_INSUFFICIENT_DATA;
        }

        return BMP_OK;
}


/**
 * Allocates memory for the next BMP in an ICO collection
 *
 * Sets proper structure values
 *
 * \param ico the ICO collection to add the image to
 * \param image a pointer to the ICO image to be initialised
 */
static bmp_result next_ico_image(ico_collection *ico, ico_image *image) {
        bmp_create(&image->bmp, &ico->bitmap_callbacks);
        image->next = ico->first;
        ico->first = image;
        return BMP_OK;
}


/**
 * Parse the icon file header
 *
 * \param ico The icon collection.
 * \param data The header data to parse.
 * \return BMP_OK on successful parse else error code
 */
static bmp_result ico_header_parse(ico_collection *ico, uint8_t *data)
{
        uint16_t count, i;
        bmp_result result;
        int area, max_area = 0;

        /* 6-byte ICO file header is:
         *
         *	+0	INT16	Reserved (should be 0)
         *	+2	UINT16	Type (1 for ICO, 2 for CUR)
         *	+4	UINT16	Number of BMPs to follow
         */
        if (ico->buffer_size < ICO_FILE_HEADER_SIZE)
                return BMP_INSUFFICIENT_DATA;
        //      if (read_int16(data, 2) != 0x0000)
        //              return BMP_DATA_ERROR;
        if (read_uint16(data, 2) != 0x0001)
                return BMP_DATA_ERROR;
        count = read_uint16(data, 4);
        if (count == 0)
                return BMP_DATA_ERROR;
        data += ICO_FILE_HEADER_SIZE;

        /* check if we have enough data for the directory */
        if (ico->buffer_size < (uint32_t)(ICO_FILE_HEADER_SIZE + (ICO_DIR_ENTRY_SIZE * count)))
                return BMP_INSUFFICIENT_DATA;

        /* Decode the BMP files.
         *
         * 16-byte ICO directory entry is:
         *
         *	+0	UINT8	Width (0 for 256 pixels)
         *	+1	UINT8	Height (0 for 256 pixels)
         *	+2	UINT8	Colour count (0 if more than 256 colours)
         *	+3	INT8	Reserved (should be 0, but may not be)
         *	+4	UINT16	Colour Planes (should be 0 or 1)
         *	+6	UINT16	Bits Per Pixel
         *	+8	UINT32	Size of BMP info header + bitmap data in bytes
         *	+12	UINT32	Offset (points to the BMP info header, not the bitmap data)
         */
        for (i = 0; i < count; i++) {
                ico_image *image;
                image = calloc(1, sizeof(ico_image));
                if (!image)
                        return BMP_INSUFFICIENT_MEMORY;
                result = next_ico_image(ico, image);
                if (result != BMP_OK)
                        return result;
                image->bmp.width = read_uint8(data, 0);
                if (image->bmp.width == 0)
                        image->bmp.width = 256;
                image->bmp.height = read_uint8(data, 1);
                if (image->bmp.height == 0)
                        image->bmp.height = 256;
                image->bmp.buffer_size = read_uint32(data, 8);
                image->bmp.bmp_data = ico->ico_data + read_uint32(data, 12);
                image->bmp.ico = true;
                data += ICO_DIR_ENTRY_SIZE;

                /* Ensure that the bitmap data resides in the buffer */
                if (image->bmp.bmp_data - ico->ico_data >= 0 &&
                    (uint32_t)(image->bmp.bmp_data -
                               ico->ico_data) >= ico->buffer_size)
                        return BMP_DATA_ERROR;

                /* Ensure that we have sufficient data to read the bitmap */
                if (image->bmp.buffer_size - ICO_DIR_ENTRY_SIZE >=
                    ico->buffer_size - (ico->ico_data - data))
                        return BMP_INSUFFICIENT_DATA;

                result = bmp_info_header_parse(&image->bmp,
                                               image->bmp.bmp_data);
                if (result != BMP_OK)
                        return result;

                /* adjust the size based on the images available */
                area = image->bmp.width * image->bmp.height;
                if (area > max_area) {
                        ico->width = image->bmp.width;
                        ico->height = image->bmp.height;
                        max_area = area;
                }
        }
        return BMP_OK;
}


/**
 * Decode BMP data stored in 32bpp colour.
 *
 * \param bmp	the BMP image to decode
 * \param start	the data to decode, updated to last byte read on success
 * \param bytes	the number of bytes of data available
 * \return	BMP_OK on success
 *		BMP_INSUFFICIENT_DATA if the bitmap data ends unexpectedly;
 *			in this case, the image may be partially viewable
 */
static bmp_result bmp_decode_rgb32(bmp_image *bmp, uint8_t **start, int bytes)
{
        uint8_t *top, *bottom, *end, *data;
        uint32_t *scanline;
        uint32_t x, y;
        uint32_t swidth;
        intptr_t addr;
        uint8_t i;
        uint32_t word;

        assert(bmp->bpp == 32);

        data = *start;
        swidth = bmp->bitmap_callbacks.bitmap_get_bpp(bmp->bitmap) * bmp->width;
        top = bmp->bitmap_callbacks.bitmap_get_buffer(bmp->bitmap);
        if (!top)
                return BMP_INSUFFICIENT_MEMORY;
        bottom = top + (uint64_t)swidth * (bmp->height - 1);
        end = data + bytes;
        addr = ((intptr_t)data) & 3;
        bmp->decoded = true;

        /* Determine transparent index */
        if (bmp->limited_trans) {
                if ((data + 4) > end)
                        return BMP_INSUFFICIENT_DATA;
                if (bmp->encoding == BMP_ENCODING_BITFIELDS)
                        bmp->transparent_index = read_uint32(data, 0);
                else
                        bmp->transparent_index = data[2] | (data[1] << 8) | (data[0] << 16);
        }

        for (y = 0; y < bmp->height; y++) {
                while (addr != (((intptr_t)data) & 3))
                        data++;
                if ((data + (4 * bmp->width)) > end)
                        return BMP_INSUFFICIENT_DATA;
                if (bmp->reversed)
                        scanline = (void *)(top + (y * swidth));
                else
                        scanline = (void *)(bottom - (y * swidth));
                if (bmp->encoding == BMP_ENCODING_BITFIELDS) {
                        for (x = 0; x < bmp->width; x++) {
                                word = read_uint32(data, 0);
                                for (i = 0; i < 4; i++)
                                        if (bmp->shift[i] > 0)
                                                scanline[x] |= ((word & bmp->mask[i]) << bmp->shift[i]);
                                        else
                                                scanline[x] |= ((word & bmp->mask[i]) >> (-bmp->shift[i]));
                                /* 32-bit BMPs have alpha masks, but sometimes they're not utilized */
                                if (bmp->opaque)
                                        scanline[x] |= (0xff << 24);
                                data += 4;
                                scanline[x] = read_uint32((uint8_t *)&scanline[x],0);
                        }
                } else {
                        for (x = 0; x < bmp->width; x++) {
                                scanline[x] = data[2] | (data[1] << 8) | (data[0] << 16);
                                if ((bmp->limited_trans) && (scanline[x] == bmp->transparent_index)) {
                                        scanline[x] = bmp->trans_colour;
                                }
                                if (bmp->opaque) {
                                        scanline[x] |= (0xff << 24);
                                }
                                data += 4;
                                scanline[x] = read_uint32((uint8_t *)&scanline[x],0);
                        }
                }
        }
        *start = data;
        return BMP_OK;
}


/**
 * Decode BMP data stored in 24bpp colour.
 *
 * \param bmp	the BMP image to decode
 * \param start	the data to decode, updated to last byte read on success
 * \param bytes	the number of bytes of data available
 * \return	BMP_OK on success
 *		BMP_INSUFFICIENT_DATA if the bitmap data ends unexpectedly;
 *			in this case, the image may be partially viewable
 */
static bmp_result bmp_decode_rgb24(bmp_image *bmp, uint8_t **start, int bytes)
{
        uint8_t *top, *bottom, *end, *data;
        uint32_t *scanline;
        uint32_t x, y;
        uint32_t swidth;
        intptr_t addr;

        assert(bmp->encoding == BMP_ENCODING_RGB);
        assert(bmp->bpp == 24);

        data = *start;
        swidth = bmp->bitmap_callbacks.bitmap_get_bpp(bmp->bitmap) * bmp->width;
        top = bmp->bitmap_callbacks.bitmap_get_buffer(bmp->bitmap);
        if (!top) {
                return BMP_INSUFFICIENT_MEMORY;
        }

        bottom = top + (uint64_t)swidth * (bmp->height - 1);
        end = data + bytes;
        addr = ((intptr_t)data) & 3;
        bmp->decoded = true;

        /* Determine transparent index */
        if (bmp->limited_trans) {
                if ((data + 3) > end) {
                        return BMP_INSUFFICIENT_DATA;
                }

                bmp->transparent_index = data[2] | (data[1] << 8) | (data[0] << 16);
        }

        for (y = 0; y < bmp->height; y++) {
                while (addr != (((intptr_t)data) & 3)) {
                        data++;
                }

                if ((data + (3 * bmp->width)) > end) {
                        return BMP_INSUFFICIENT_DATA;
                }

                if (bmp->reversed) {
                        scanline = (void *)(top + (y * swidth));
                } else {
                        scanline = (void *)(bottom - (y * swidth));
                }

                for (x = 0; x < bmp->width; x++) {
                        scanline[x] = data[2] | (data[1] << 8) | (data[0] << 16);
                        if ((bmp->limited_trans) && (scanline[x] == bmp->transparent_index)) {
                                scanline[x] = bmp->trans_colour;
                        } else {
                                scanline[x] |= (0xff << 24);
                        }
                        data += 3;
                        scanline[x] = read_uint32((uint8_t *)&scanline[x],0);
                }

        }
        *start = data;
        return BMP_OK;
}


/**
 * Decode BMP data stored in 16bpp colour.
 *
 * \param bmp	the BMP image to decode
 * \param start	the data to decode, updated to last byte read on success
 * \param bytes	the number of bytes of data available
 * \return	BMP_OK on success
 *		BMP_INSUFFICIENT_DATA if the bitmap data ends unexpectedly;
 *			in this case, the image may be partially viewable
 */
static bmp_result bmp_decode_rgb16(bmp_image *bmp, uint8_t **start, int bytes)
{
        uint8_t *top, *bottom, *end, *data;
        uint32_t *scanline;
        uint32_t x, y, swidth;
        intptr_t addr;
        uint8_t i;
        uint16_t word;

        data = *start;
        swidth = bmp->bitmap_callbacks.bitmap_get_bpp(bmp->bitmap) * bmp->width;
        top = bmp->bitmap_callbacks.bitmap_get_buffer(bmp->bitmap);
        if (!top)
                return BMP_INSUFFICIENT_MEMORY;
        bottom = top + (uint64_t)swidth * (bmp->height - 1);
        end = data + bytes;
        addr = ((intptr_t)data) & 3;
        bmp->decoded = true;

        /* Determine transparent index */
        if (bmp->limited_trans) {
                if ((data + 2) > end)
                        return BMP_INSUFFICIENT_DATA;
                bmp->transparent_index = read_uint16(data, 0);
        }

        for (y = 0; y < bmp->height; y++) {
                while (addr != (((intptr_t)data) & 3))
                        data += 2;
                if ((data + (2 * bmp->width)) > end)
                        return BMP_INSUFFICIENT_DATA;
                if (bmp->reversed)
                        scanline = (void *)(top + (y * swidth));
                else
                        scanline = (void *)(bottom - (y * swidth));
                if (bmp->encoding == BMP_ENCODING_BITFIELDS) {
                        for (x = 0; x < bmp->width; x++) {
                                word = read_uint16(data, 0);
                                if ((bmp->limited_trans) && (word == bmp->transparent_index))
                                        scanline[x] = bmp->trans_colour;
                                else {
                                        scanline[x] = 0;
                                        for (i = 0; i < 4; i++)
                                                if (bmp->shift[i] > 0)
                                                        scanline[x] |= ((word & bmp->mask[i]) << bmp->shift[i]);
                                                else
                                                        scanline[x] |= ((word & bmp->mask[i]) >> (-bmp->shift[i]));
                                        if (bmp->opaque)
                                                scanline[x] |= (0xff << 24);
                                }
                                data += 2;
                                scanline[x] = read_uint32((uint8_t *)&scanline[x],0);
                        }
                } else {
                        for (x = 0; x < bmp->width; x++) {
                                word = read_uint16(data, 0);
                                if ((bmp->limited_trans) && (word == bmp->transparent_index))
                                        scanline[x] = bmp->trans_colour;
                                else {
                                        /* 16-bit RGB defaults to RGB555 */
                                        scanline[x] = ((word & (31 << 0)) << 19) |
                                                      ((word & (31 << 5)) << 6) |
                                                      ((word & (31 << 10)) >> 7);
                                }
                                if (bmp->opaque)
                                        scanline[x] |= (0xff << 24);
                                data += 2;
                                scanline[x] = read_uint32((uint8_t *)&scanline[x],0);
                        }
                }
        }
        *start = data;
        return BMP_OK;
}


/**
 * Decode BMP data stored with a palette and in 8bpp colour or less.
 *
 * \param bmp	the BMP image to decode
 * \param start	the data to decode, updated to last byte read on success
 * \param bytes	the number of bytes of data available
 * \return	BMP_OK on success
 *		BMP_INSUFFICIENT_DATA if the bitmap data ends unexpectedly;
 *			in this case, the image may be partially viewable
 */
static bmp_result bmp_decode_rgb(bmp_image *bmp, uint8_t **start, int bytes)
{
        uint8_t *top, *bottom, *end, *data;
        uint32_t *scanline;
        intptr_t addr;
        uint32_t x, y, swidth;
        uint8_t bit_shifts[8];
        uint8_t ppb = 8 / bmp->bpp;
        uint8_t bit_mask = (1 << bmp->bpp) - 1;
        uint8_t cur_byte = 0, bit, i;

        for (i = 0; i < ppb; i++)
                bit_shifts[i] = 8 - ((i + 1) * bmp->bpp);

        data = *start;
        swidth = bmp->bitmap_callbacks.bitmap_get_bpp(bmp->bitmap) * bmp->width;
        top = bmp->bitmap_callbacks.bitmap_get_buffer(bmp->bitmap);
        if (!top)
                return BMP_INSUFFICIENT_MEMORY;
        bottom = top + (uint64_t)swidth * (bmp->height - 1);
        end = data + bytes;
        addr = ((intptr_t)data) & 3;
        bmp->decoded = true;

        /* Determine transparent index */
        if (bmp->limited_trans) {
                uint32_t idx = (*data >> bit_shifts[0]) & bit_mask;
                if (idx >= bmp->colours)
                        return BMP_DATA_ERROR;
                bmp->transparent_index = bmp->colour_table[idx];
        }

        for (y = 0; y < bmp->height; y++) {
                while (addr != (((intptr_t)data) & 3))
                        data++;
                bit = 8;
                if ((data + (bmp->width / ppb)) > end)
                        return BMP_INSUFFICIENT_DATA;
                if (bmp->reversed)
                        scanline = (void *)(top + (y * swidth));
                else
                        scanline = (void *)(bottom - (y * swidth));
                for (x = 0; x < bmp->width; x++) {
                        uint32_t idx;
                        if (bit >= ppb) {
                                bit = 0;
                                cur_byte = *data++;
                        }
                        idx = (cur_byte >> bit_shifts[bit++]) & bit_mask;
                        if (idx < bmp->colours) {
                                /* ensure colour table index is in bounds */
                                scanline[x] = bmp->colour_table[idx];
                                if ((bmp->limited_trans) &&
                                    (scanline[x] == bmp->transparent_index)) {
                                        scanline[x] = bmp->trans_colour;
                                }
                        }
                }
        }
        *start = data;
        return BMP_OK;
}


/**
 * Decode a 1bpp mask for an ICO
 *
 * \param bmp	the BMP image to decode
 * \param data	the data to decode
 * \param bytes	the number of bytes of data available
 * \return BMP_OK on success
 */
static bmp_result bmp_decode_mask(bmp_image *bmp, uint8_t *data, int bytes)
{
        uint8_t *top, *bottom, *end;
        uint32_t *scanline;
        intptr_t addr;
        uint32_t x, y, swidth;
        uint32_t cur_byte = 0;

        swidth = bmp->bitmap_callbacks.bitmap_get_bpp(bmp->bitmap) * bmp->width;
        top = bmp->bitmap_callbacks.bitmap_get_buffer(bmp->bitmap);
        if (!top)
                return BMP_INSUFFICIENT_MEMORY;
        bottom = top + (uint64_t)swidth * (bmp->height - 1);
        end = data + bytes;
        addr = ((intptr_t)data) & 3;

        for (y = 0; y < bmp->height; y++) {
                while (addr != (((intptr_t)data) & 3))
                        data++;
                if ((data + (bmp->width >> 3)) > end)
                        return BMP_INSUFFICIENT_DATA;
                scanline = (void *)(bottom - (y * swidth));
                for (x = 0; x < bmp->width; x++) {
                        if ((x & 7) == 0)
                                cur_byte = *data++;
                        if ((cur_byte & 128) == 0) {
                                scanline[x] = read_uint32((uint8_t *)&scanline[x], 0);
                                scanline[x] |= (0xff << 24);
                                scanline[x] = read_uint32((uint8_t *)&scanline[x], 0);
                        }
                        cur_byte = cur_byte << 1;
                }
        }
        return BMP_OK;
}


/**
 * Decode BMP data stored encoded in RLE8.
 *
 * \param bmp	the BMP image to decode
 * \param data	the data to decode
 * \param bytes	the number of bytes of data available
 * \return	BMP_OK on success
 *		BMP_INSUFFICIENT_DATA if the bitmap data ends unexpectedly;
 *			in this case, the image may be partially viewable
 */
static bmp_result
bmp_decode_rle8(bmp_image *bmp, uint8_t *data, int bytes)
{
        uint8_t *top, *bottom, *end;
        uint32_t *scanline;
        uint32_t swidth;
        uint32_t i, length, pixels_left;
        uint32_t x = 0, y = 0, last_y = 0;
        uint32_t pixel = 0;

        if (bmp->ico)
                return BMP_DATA_ERROR;

        swidth = bmp->bitmap_callbacks.bitmap_get_bpp(bmp->bitmap) * bmp->width;
        top = bmp->bitmap_callbacks.bitmap_get_buffer(bmp->bitmap);
        if (!top)
                return BMP_INSUFFICIENT_MEMORY;
        bottom = top + (uint64_t)swidth * (bmp->height - 1);
        end = data + bytes;
        bmp->decoded = true;

        do {
                if (data + 2 > end)
                        return BMP_INSUFFICIENT_DATA;
                length = *data++;
                if (length == 0) {
                        length = *data++;
                        switch (length) {
                        case 0:
                                /* 00 - 00 means end of scanline */
                                x = 0;
                                if (last_y == y) {
                                        y++;
                                        if (y >= bmp->height)
                                                return BMP_DATA_ERROR;
                                }
                                last_y = y;
                                break;

                        case 1:
                                /* 00 - 01 means end of RLE data */
                                return BMP_OK;

                        case 2:
                                /* 00 - 02 - XX - YY means move cursor */
                                if (data + 2 > end)
                                        return BMP_INSUFFICIENT_DATA;
                                x += *data++;
                                if (x >= bmp->width)
                                        return BMP_DATA_ERROR;
                                y += *data++;
                                if (y >= bmp->height)
                                        return BMP_DATA_ERROR;
                                break;

                        default:
                                /* 00 - NN means escape NN pixels */
                                if (bmp->reversed) {
                                        pixels_left = (bmp->height - y) * bmp->width - x;
                                        scanline = (void *)(top + (y * swidth));
                                } else {
                                        pixels_left = (y + 1) * bmp->width - x;
                                        scanline = (void *)(bottom - (y * swidth));
                                }
                                if (length > pixels_left)
                                        length = pixels_left;
                                if (data + length > end)
                                        return BMP_INSUFFICIENT_DATA;

                                /* the following code could be easily optimised
                                 * by simply checking the bounds on entry and
                                 * using some simple copying routines if so
                                 */
                                for (i = 0; i < length; i++) {
                                        uint32_t idx = (uint32_t) *data++;
                                        if (x >= bmp->width) {
                                                x = 0;
                                                y++;
                                                if (y >= bmp->height)
                                                        return BMP_DATA_ERROR;
                                                if (bmp->reversed) {
                                                        scanline += bmp->width;
                                                } else {
                                                        scanline -= bmp->width;
                                                }
                                        }
                                        if (idx >= bmp->colours)
                                                return BMP_DATA_ERROR;
                                        scanline[x++] = bmp->colour_table[idx];
                                }

                                if ((length & 1) && (*data++ != 0x00))
                                        return BMP_DATA_ERROR;

                                break;
                        }
                } else {
                        uint32_t idx;

                        /* NN means perform RLE for NN pixels */
                        if (bmp->reversed) {
                                pixels_left = (bmp->height - y) * bmp->width - x;
                                scanline = (void *)(top + (y * swidth));
                        } else {
                                pixels_left = (y + 1) * bmp->width - x;
                                scanline = (void *)(bottom - (y * swidth));
                        }
                        if (length > pixels_left)
                                length = pixels_left;

                        /* boundary checking */
                        if (data + 1 > end)
                                return BMP_INSUFFICIENT_DATA;

                        /* the following code could be easily optimised by
                         * simply checking the bounds on entry and using some
                         * simply copying routines if so
                         */
                        idx = (uint32_t) *data++;
                        if (idx >= bmp->colours)
                                return BMP_DATA_ERROR;

                        pixel = bmp->colour_table[idx];
                        for (i = 0; i < length; i++) {
                                if (x >= bmp->width) {
                                        x = 0;
                                        y++;
                                        if (y >= bmp->height)
                                                return BMP_DATA_ERROR;
                                        if (bmp->reversed) {
                                                scanline += bmp->width;
                                        } else {
                                                scanline -= bmp->width;
                                        }
                                }
                                scanline[x++] = pixel;
                        }
                }
        } while (data < end);

        return BMP_OK;
}


/**
 * Decode BMP data stored encoded in RLE4.
 *
 * \param bmp	the BMP image to decode
 * \param data	the data to decode
 * \param bytes	the number of bytes of data available
 * \return	BMP_OK on success
 *		BMP_INSUFFICIENT_DATA if the bitmap data ends unexpectedly;
 *			in this case, the image may be partially viewable
 */
static bmp_result
bmp_decode_rle4(bmp_image *bmp, uint8_t *data, int bytes)
{
        uint8_t *top, *bottom, *end;
        uint32_t *scanline;
        uint32_t swidth;
        uint32_t i, length, pixels_left;
        uint32_t x = 0, y = 0, last_y = 0;
        uint32_t pixel = 0, pixel2;

        if (bmp->ico)
                return BMP_DATA_ERROR;

        swidth = bmp->bitmap_callbacks.bitmap_get_bpp(bmp->bitmap) * bmp->width;
        top = bmp->bitmap_callbacks.bitmap_get_buffer(bmp->bitmap);
        if (!top)
                return BMP_INSUFFICIENT_MEMORY;
        bottom = top + (uint64_t)swidth * (bmp->height - 1);
        end = data + bytes;
        bmp->decoded = true;

        do {
                if (data + 2 > end)
                        return BMP_INSUFFICIENT_DATA;
                length = *data++;
                if (length == 0) {
                        length = *data++;
                        switch (length) {
                        case 0:
                                /* 00 - 00 means end of scanline */
                                x = 0;
                                if (last_y == y) {
                                        y++;
                                        if (y >= bmp->height)
                                                return BMP_DATA_ERROR;
                                }
                                last_y = y;
                                break;

                        case 1:
                                /* 00 - 01 means end of RLE data */
                                return BMP_OK;

                        case 2:
                                /* 00 - 02 - XX - YY means move cursor */
                                if (data + 2 > end)
                                        return BMP_INSUFFICIENT_DATA;
                                x += *data++;
                                if (x >= bmp->width)
                                        return BMP_DATA_ERROR;
                                y += *data++;
                                if (y >= bmp->height)
                                        return BMP_DATA_ERROR;
                                break;

                        default:
                                /* 00 - NN means escape NN pixels */
                                if (bmp->reversed) {
                                        pixels_left = (bmp->height - y) * bmp->width - x;
                                        scanline = (void *)(top + (y * swidth));
                                } else {
                                        pixels_left = (y + 1) * bmp->width - x;
                                        scanline = (void *)(bottom - (y * swidth));
                                }
                                if (length > pixels_left)
                                        length = pixels_left;
                                if (data + ((length + 1) / 2) > end)
                                        return BMP_INSUFFICIENT_DATA;

                                /* the following code could be easily optimised
                                 * by simply checking the bounds on entry and
                                 * using some simple copying routines
                                 */

                                for (i = 0; i < length; i++) {
                                        if (x >= bmp->width) {
                                                x = 0;
                                                y++;
                                                if (y >= bmp->height)
                                                        return BMP_DATA_ERROR;
                                                if (bmp->reversed) {
                                                        scanline += bmp->width;
                                                } else {
                                                        scanline -= bmp->width;
                                                }

                                        }
                                        if ((i & 1) == 0) {
                                                pixel = *data++;
                                                if ((pixel >> 4) >= bmp->colours)
                                                        return BMP_DATA_ERROR;
                                                scanline[x++] = bmp->colour_table
                                                                [pixel >> 4];
                                        } else {
                                                if ((pixel & 0xf) >= bmp->colours)
                                                        return BMP_DATA_ERROR;
                                                scanline[x++] = bmp->colour_table
                                                                [pixel & 0xf];
                                        }
                                }
                                length = (length + 1) >> 1;

                                if ((length & 1) && (*data++ != 0x00))
                                        return BMP_DATA_ERROR;

                                break;
                        }
                } else {
                        /* NN means perform RLE for NN pixels */
                        if (bmp->reversed) {
                                pixels_left = (bmp->height - y) * bmp->width - x;
                                scanline = (void *)(top + (y * swidth));
                        } else {
                                pixels_left = (y + 1) * bmp->width - x;
                                scanline = (void *)(bottom - (y * swidth));
                        }
                        if (length > pixels_left)
                                length = pixels_left;

                        /* boundary checking */
                        if (data + 1 > end)
                                return BMP_INSUFFICIENT_DATA;

                        /* the following code could be easily optimised by
                         * simply checking the bounds on entry and using some
                         * simple copying routines
                         */

                        pixel2 = *data++;
                        if ((pixel2 >> 4) >= bmp->colours ||
                            (pixel2 & 0xf) >= bmp->colours)
                                return BMP_DATA_ERROR;
                        pixel = bmp->colour_table[pixel2 >> 4];
                        pixel2 = bmp->colour_table[pixel2 & 0xf];
                        for (i = 0; i < length; i++) {
                                if (x >= bmp->width) {
                                        x = 0;
                                        y++;
                                        if (y >= bmp->height)
                                                return BMP_DATA_ERROR;
                                        if (bmp->reversed) {
                                                scanline += bmp->width;
                                        } else {
                                                scanline -= bmp->width;
                                        }
                                }
                                if ((i & 1) == 0)
                                        scanline[x++] = pixel;
                                else
                                        scanline[x++] = pixel2;
                        }

                }
        } while (data < end);

        return BMP_OK;
}


/* exported interface documented in libnsbmp.h */
bmp_result
bmp_create(bmp_image *bmp,
           bmp_bitmap_callback_vt *bitmap_callbacks)
{
        memset(bmp, 0, sizeof(bmp_image));
        bmp->bitmap_callbacks = *bitmap_callbacks;

        return BMP_OK;
}


/* exported interface documented in libnsbmp.h */
bmp_result
ico_collection_create(ico_collection *ico,
                      bmp_bitmap_callback_vt *bitmap_callbacks)
{

        memset(ico, 0, sizeof(ico_collection));
        ico->bitmap_callbacks = *bitmap_callbacks;

        return BMP_OK;
}


/* exported interface documented in libnsbmp.h */
bmp_result bmp_analyse(bmp_image *bmp, size_t size, uint8_t *data)
{
        bmp_result res;

        /* ensure we aren't already initialised */
        if (bmp->bitmap) {
                return BMP_OK;
        }

        /* initialize source data values */
        bmp->buffer_size = size;
        bmp->bmp_data = data;

        res = bmp_file_header_parse(bmp, data);
        if (res == BMP_OK) {
                res = bmp_info_header_parse(bmp, data + BMP_FILE_HEADER_SIZE);
        }
        return res;
}


/* exported interface documented in libnsbmp.h */
bmp_result ico_analyse(ico_collection *ico, size_t size, uint8_t *data)
{
        /* ensure we aren't already initialised */
        if (ico->first)
                return BMP_OK;

        /* initialize values */
        ico->buffer_size = size;
        ico->ico_data = data;

        return ico_header_parse(ico, data);
}


/* exported interface documented in libnsbmp.h */
bmp_result bmp_decode(bmp_image *bmp)
{
        uint8_t *data;
        uint32_t bytes;
        bmp_result result = BMP_OK;

        assert(bmp->bitmap);

        data = bmp->bmp_data + bmp->bitmap_offset;
        bytes = bmp->buffer_size - bmp->bitmap_offset;

        switch (bmp->encoding) {
        case BMP_ENCODING_RGB:
                switch (bmp->bpp) {
                case 32:
                        result = bmp_decode_rgb32(bmp, &data, bytes);
                        break;

                case 24:
                        result = bmp_decode_rgb24(bmp, &data, bytes);
                        break;

                case 16:
                        result = bmp_decode_rgb16(bmp, &data, bytes);
                        break;

                default:
                        result = bmp_decode_rgb(bmp, &data, bytes);
                        break;
                }
                break;

        case BMP_ENCODING_RLE8:
                result = bmp_decode_rle8(bmp, data, bytes);
                break;

        case BMP_ENCODING_RLE4:
                result = bmp_decode_rle4(bmp, data, bytes);
                break;

        case BMP_ENCODING_BITFIELDS:
                switch (bmp->bpp) {
                case 32:
                        result = bmp_decode_rgb32(bmp, &data, bytes);
                        break;

                case 16:
                        result = bmp_decode_rgb16(bmp, &data, bytes);
                        break;

                default:
                        result = BMP_DATA_ERROR;
                        break;
                }
                break;
        }

        if ((!bmp->ico) || (result != BMP_OK))
                return result;

        bytes = (uintptr_t)bmp->bmp_data + bmp->buffer_size - (uintptr_t)data;
        return bmp_decode_mask(bmp, data, bytes);
}


/* exported interface documented in libnsbmp.h */
bmp_result bmp_decode_trans(bmp_image *bmp, uint32_t colour)
{
        bmp->limited_trans = true;
        bmp->trans_colour = colour;
        return bmp_decode(bmp);
}


/* exported interface documented in libnsbmp.h */
bmp_image *ico_find(ico_collection *ico, uint16_t width, uint16_t height)
{
        bmp_image *bmp = NULL;
        ico_image *image;
        int x, y, cur, distance = (1 << 24);

        if (width == 0)
                width = ico->width;
        if (height == 0)
                height = ico->height;
        for (image = ico->first; image; image = image->next) {
                if ((image->bmp.width == width) && (image->bmp.height == height))
                        return &image->bmp;
                x = image->bmp.width - width;
                y = image->bmp.height - height;
                cur = (x * x) + (y * y);
                if (cur < distance) {
                        distance = cur;
                        bmp = &image->bmp;
                }
        }
        return bmp;
}


/* exported interface documented in libnsbmp.h */
void bmp_finalise(bmp_image *bmp)
{
        if (bmp->bitmap)
                bmp->bitmap_callbacks.bitmap_destroy(bmp->bitmap);
        bmp->bitmap = NULL;
        if (bmp->colour_table)
                free(bmp->colour_table);
        bmp->colour_table = NULL;
}


/* exported interface documented in libnsbmp.h */
void ico_finalise(ico_collection *ico)
{
        ico_image *image;

        for (image = ico->first; image; image = image->next)
                bmp_finalise(&image->bmp);
        while (ico->first) {
                image = ico->first;
                ico->first = image->next;
                free(image);
        }
}