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authorMichael Drake <michael.drake@codethink.co.uk>2017-04-05 10:38:06 (GMT)
committer Michael Drake <michael.drake@codethink.co.uk>2017-04-05 10:38:06 (GMT)
commit099b873abca6b868f159e16894f3640d40dca5aa (patch)
tree5a8d0c86954d5bc46deff890cf7551ab1f4a5989
parent4a6136b81993da5c838df13eb3b1433deb87abf4 (diff)
parentf9797e4ae82090808036b1e1ec4318d0f1bdc456 (diff)
downloadlibnsgif-099b873abca6b868f159e16894f3640d40dca5aa.tar.gz
libnsgif-099b873abca6b868f159e16894f3640d40dca5aa.tar.bz2
Merge branch 'tlsa/lzw'
-rw-r--r--include/libnsgif.h2
-rw-r--r--src/Makefile2
-rw-r--r--src/libnsgif.c368
-rw-r--r--src/lzw.c372
-rw-r--r--src/lzw.h105
-rw-r--r--test/decode_gif.c66
6 files changed, 564 insertions, 351 deletions
diff --git a/include/libnsgif.h b/include/libnsgif.h
index fd92a0a..a819fec 100644
--- a/include/libnsgif.h
+++ b/include/libnsgif.h
@@ -93,6 +93,8 @@ typedef struct gif_bitmap_callback_vt {
/** GIF animation data */
typedef struct gif_animation {
+ /** LZW decode context */
+ void *lzw_ctx;
/** callbacks for bitmap functions */
gif_bitmap_callback_vt bitmap_callbacks;
/** pointer to GIF data */
diff --git a/src/Makefile b/src/Makefile
index 0fa4dc6..cb5d31f 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -1,4 +1,4 @@
# Sources
-DIR_SOURCES := libnsgif.c
+DIR_SOURCES := libnsgif.c lzw.c
include $(NSBUILD)/Makefile.subdir
diff --git a/src/libnsgif.c b/src/libnsgif.c
index 998f8d7..6bf9956 100644
--- a/src/libnsgif.c
+++ b/src/libnsgif.c
@@ -8,6 +8,7 @@
*/
#include <stdbool.h>
+#include <stdint.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
@@ -15,6 +16,8 @@
#include "libnsgif.h"
#include "utils/log.h"
+#include "lzw.h"
+
/**
*
* \file
@@ -36,9 +39,6 @@
/** Internal flag that a frame is invalid/unprocessed */
#define GIF_INVALID_FRAME -1
-/** Maximum LZW bits available */
-#define GIF_MAX_LZW 12
-
/** Transparent colour */
#define GIF_TRANSPARENT_COLOUR 0x00
@@ -65,313 +65,6 @@
/** standard GIF header size */
#define GIF_STANDARD_HEADER_SIZE 13
-/** LZW parameters */
-struct lzw_s {
- unsigned char buf[4];
- const unsigned char *direct;
- int table[2][(1 << GIF_MAX_LZW)];
- unsigned char stack[(1 << GIF_MAX_LZW) * 2];
- unsigned char *stack_pointer;
-
- int code_size, set_code_size;
-
- int max_code, max_code_size;
-
- int clear_code, end_code;
-
- int curbit, lastbit, last_byte;
-
- int firstcode;
- int oldcode;
-
- bool zero_data_block;
- bool get_done;
-};
-
-
-/* General LZW values. They are shared for all GIFs being decoded, and thus we
- * can't handle progressive decoding efficiently without having the data for
- * each image which would use an extra 10Kb or so per GIF.
- */
-static struct lzw_s lzw_params = {
- .zero_data_block = false,
-};
-
-static struct lzw_s *lzw = &lzw_params;
-
-/**
- * get the next LZW code from the GIF
- *
- * reads codes from the input data stream coping with GIF data sub blocking
- *
- * \param[in] compressed_data LZW compressed data
- * \param[in] compressed_data_len Byte size of compressed_data
- * \param[in,out] compressed_data_pos Current position in compressed_data
- * updated on exit.
- * \param[in] code_size Number of bits in the current LZW code
- * \return The next code to process or error return code
- */
-static int gif_next_code(
- const uint8_t *compressed_data,
- uint32_t compressed_data_len,
- uint32_t *compressed_data_pos,
- int code_size)
-{
- int i, j, end, count, ret;
- uint32_t pos = *compressed_data_pos;
- const unsigned char *b;
- static const int maskTbl[16] = {
- 0x0000, 0x0001, 0x0003, 0x0007, 0x000f, 0x001f, 0x003f, 0x007f,
- 0x00ff, 0x01ff, 0x03ff, 0x07ff, 0x0fff, 0x1fff, 0x3fff, 0x7fff
- };
-
- end = lzw->curbit + code_size;
- if (end >= lzw->lastbit) {
- if (lzw->get_done) {
- return GIF_END_OF_FRAME;
- }
- lzw->buf[0] = lzw->direct[lzw->last_byte - 2];
- lzw->buf[1] = lzw->direct[lzw->last_byte - 1];
-
- /* get the next block */
- lzw->direct = compressed_data + pos;
- if (pos >= compressed_data_len) {
- return GIF_INSUFFICIENT_FRAME_DATA;
- }
-
- count = lzw->direct[0];
- lzw->zero_data_block = (count == 0);
- if ((pos + count) >= compressed_data_len) {
- return GIF_INSUFFICIENT_FRAME_DATA;
- }
-
- if (count == 0) {
- lzw->get_done = true;
- } else {
- if (pos + 3 >= compressed_data_len) {
- return GIF_INSUFFICIENT_FRAME_DATA;
- }
- lzw->direct -= 1;
- lzw->buf[2] = lzw->direct[2];
- lzw->buf[3] = lzw->direct[3];
- }
- pos += count + 1;
-
- /* update our variables */
- lzw->last_byte = 2 + count;
- lzw->curbit = (lzw->curbit - lzw->lastbit) + 16;
- lzw->lastbit = (2 + count) << 3;
- end = lzw->curbit + code_size;
- }
-
- i = lzw->curbit >> 3;
- if (i < 2) {
- b = lzw->buf;
- } else {
- b = lzw->direct;
- }
-
- ret = b[i];
- j = (end >> 3) - 1;
- if (i <= j) {
- ret |= (b[i + 1] << 8);
- if (i < j) {
- ret |= (b[i + 2] << 16);
- }
- }
- ret = (ret >> (lzw->curbit % 8)) & maskTbl[code_size];
- lzw->curbit += code_size;
-
- *compressed_data_pos = pos;
- return ret;
-}
-
-
-/**
- * Clear LZW code dictionary
- *
- * \param[in] compressed_data LZW compressed data
- * \param[in] compressed_data_len Byte size of compressed_data
- * \param[in,out] compressed_data_pos Current position in compressed_data
- * updated on exit.
- * \return GIF_OK or error code.
- */
-static gif_result gif_clear_codes_LZW(
- const uint8_t *compressed_data,
- uint32_t compressed_data_len,
- uint32_t *compressed_data_pos)
-{
- int i;
- int code;
-
- if (lzw->clear_code >= (1 << GIF_MAX_LZW)) {
- lzw->stack_pointer = lzw->stack;
- return GIF_FRAME_DATA_ERROR;
- }
-
- /* initialise our table */
- memset(lzw->table, 0x00, (1 << GIF_MAX_LZW) * 8);
- for (i = 0; i < lzw->clear_code; ++i) {
- lzw->table[1][i] = i;
- }
-
- /* reset LZW parameters */
- lzw->code_size = lzw->set_code_size + 1;
- lzw->max_code_size = lzw->clear_code << 1;
- lzw->max_code = lzw->clear_code + 2;
- lzw->stack_pointer = lzw->stack;
-
- /* process repeated clear codes */
- do {
- code = gif_next_code(compressed_data, compressed_data_len,
- compressed_data_pos, lzw->code_size);
- if (code < 0) {
- return code;
- }
- } while (code == lzw->clear_code);
- lzw->firstcode = lzw->oldcode = code;
-
- *lzw->stack_pointer++ = lzw->firstcode;
-
- return GIF_OK;
-}
-
-
-/**
- * Initialise LZW
- *
- * This initialises a LZW context ready to commence decompression.
- *
- * \param[in] compressed_data LZW compressed data
- * \param[in] compressed_data_len Byte size of compressed_data
- * \param[in,out] compressed_data_pos Current position in compressed_data
- * updated on exit.
- * \param[in] initial_code_size Size of codes used on clearing of code dictionary
- */
-static gif_result gif_initialise_LZW(
- const uint8_t *compressed_data,
- uint32_t compressed_data_len,
- uint32_t *compressed_data_pos,
- int initial_code_size)
-{
- lzw->set_code_size = initial_code_size;
- lzw->code_size = lzw->set_code_size + 1;
- lzw->clear_code = (1 << lzw->set_code_size);
- lzw->end_code = lzw->clear_code + 1;
- lzw->max_code_size = lzw->clear_code << 1;
- lzw->max_code = lzw->clear_code + 2;
- lzw->curbit = lzw->lastbit = 0;
- lzw->last_byte = 2;
- lzw->get_done = false;
- lzw->direct = lzw->buf;
-
- return gif_clear_codes_LZW(compressed_data,
- compressed_data_len,
- compressed_data_pos);
-}
-
-/**
- * fill the LZW stack with decompressed data
- *
- * \param[in] compressed_data LZW compressed data
- * \param[in] compressed_data_len Byte size of compressed_data
- * \param[in,out] compressed_data_pos Current position in compressed_data
- * updated on exit.
- * \return true on sucessful decode of the next LZW code else false.
- */
-static gif_result gif_next_LZW(
- const uint8_t *compressed_data,
- uint32_t compressed_data_len,
- uint32_t *compressed_data_pos)
-{
- int code, incode;
- int block_size;
- int new_code;
-
- code = gif_next_code(compressed_data, compressed_data_len,
- compressed_data_pos, lzw->code_size);
- if (code < 0) {
- return code;
- }
-
- if (code == lzw->clear_code) {
- return gif_clear_codes_LZW(compressed_data,
- compressed_data_len,
- compressed_data_pos);
- }
-
- if (code == lzw->end_code) {
- /* skip to the end of our data so multi-image GIFs work */
- if (lzw->zero_data_block) {
- return GIF_FRAME_DATA_ERROR;
- }
- block_size = 0;
- while (block_size != 1 &&
- *compressed_data_pos < compressed_data_len) {
- block_size = compressed_data[*compressed_data_pos] + 1;
- *compressed_data_pos += block_size;
- }
- return GIF_FRAME_DATA_ERROR;
- }
-
- incode = code;
- if (code >= lzw->max_code) {
- if (lzw->stack_pointer >= lzw->stack + ((1 << GIF_MAX_LZW) * 2)) {
- return GIF_FRAME_DATA_ERROR;
- }
- *lzw->stack_pointer++ = lzw->firstcode;
- code = lzw->oldcode;
- }
-
- /* The following loop is the most important in the GIF decoding cycle
- * as every single pixel passes through it.
- *
- * Note: our stack is always big enough to hold a complete decompressed
- * chunk.
- */
- while (code >= lzw->clear_code) {
- if (lzw->stack_pointer >= lzw->stack + ((1 << GIF_MAX_LZW) * 2) ||
- code >= (1 << GIF_MAX_LZW)) {
- return GIF_FRAME_DATA_ERROR;
- }
- *lzw->stack_pointer++ = lzw->table[1][code];
- new_code = lzw->table[0][code];
- if (new_code < lzw->clear_code) {
- code = new_code;
- break;
- }
-
- if (lzw->stack_pointer >= lzw->stack + ((1 << GIF_MAX_LZW) * 2) ||
- new_code >= (1 << GIF_MAX_LZW)) {
- return GIF_FRAME_DATA_ERROR;
- }
- *lzw->stack_pointer++ = lzw->table[1][new_code];
- code = lzw->table[0][new_code];
- if (code == new_code) {
- return GIF_FRAME_DATA_ERROR;
- }
- }
-
- if (lzw->stack_pointer >= lzw->stack + ((1 << GIF_MAX_LZW) * 2)) {
- return GIF_FRAME_DATA_ERROR;
- }
- *lzw->stack_pointer++ = lzw->firstcode = lzw->table[1][code];
-
- code = lzw->max_code;
- if (code < (1 << GIF_MAX_LZW)) {
- lzw->table[0][code] = lzw->oldcode;
- lzw->table[1][code] = lzw->firstcode;
- ++lzw->max_code;
- if ((lzw->max_code >= lzw->max_code_size) &&
- (lzw->max_code_size < (1 << GIF_MAX_LZW))) {
- lzw->max_code_size = lzw->max_code_size << 1;
- ++lzw->code_size;
- }
- }
- lzw->oldcode = incode;
- return GIF_OK;
-}
-
/**
* Updates the sprite memory size
@@ -725,7 +418,7 @@ static gif_result gif_initialise_frame(gif_animation *gif)
if (gif_bytes < 1) {
return GIF_INSUFFICIENT_FRAME_DATA;
}
- if (gif_data[0] > GIF_MAX_LZW) {
+ if (gif_data[0] > LZW_CODE_MAX) {
return GIF_DATA_ERROR;
}
@@ -863,7 +556,19 @@ static unsigned int gif_interlaced_line(int height, int y) {
}
-
+static gif_result gif_error_from_lzw(lzw_result l_res)
+{
+ static const gif_result g_res[] = {
+ [LZW_OK] = GIF_OK,
+ [LZW_OK_EOD] = GIF_END_OF_FRAME,
+ [LZW_NO_MEM] = GIF_INSUFFICIENT_MEMORY,
+ [LZW_NO_DATA] = GIF_INSUFFICIENT_FRAME_DATA,
+ [LZW_EOI_CODE] = GIF_FRAME_DATA_ERROR,
+ [LZW_BAD_ICODE] = GIF_FRAME_DATA_ERROR,
+ [LZW_BAD_CODE] = GIF_FRAME_DATA_ERROR,
+ };
+ return g_res[l_res];
+}
/**
@@ -878,7 +583,6 @@ gif_internal_decode_frame(gif_animation *gif,
unsigned int frame,
bool clear_image)
{
- gif_result res;
unsigned int index = 0;
unsigned char *gif_data, *gif_end;
int gif_bytes;
@@ -1038,6 +742,10 @@ gif_internal_decode_frame(gif_animation *gif,
/* If we are clearing the image we just clear, if not decode */
if (!clear_image) {
+ lzw_result res;
+ const uint8_t *stack_base;
+ const uint8_t *stack_pos;
+
/* Ensure we have enough data for a 1-byte LZW code size +
* 1-byte gif trailer
*/
@@ -1114,10 +822,11 @@ gif_internal_decode_frame(gif_animation *gif,
gif->buffer_position = (gif_data - gif->gif_data) + 1;
/* Initialise the LZW decoding */
- res = gif_initialise_LZW(gif->gif_data, gif->buffer_size,
- &gif->buffer_position, gif_data[0]);
- if (res != GIF_OK) {
- return res;
+ res = lzw_decode_init(gif->lzw_ctx, gif->gif_data,
+ gif->buffer_size, gif->buffer_position,
+ gif_data[0], &stack_base, &stack_pos);
+ if (res != LZW_OK) {
+ return gif_error_from_lzw(res);
}
/* Decompress the data */
@@ -1135,14 +844,14 @@ gif_internal_decode_frame(gif_animation *gif,
*/
x = width;
while (x > 0) {
- burst_bytes = (lzw->stack_pointer - lzw->stack);
+ burst_bytes = (stack_pos - stack_base);
if (burst_bytes > 0) {
if (burst_bytes > x) {
burst_bytes = x;
}
x -= burst_bytes;
while (burst_bytes-- > 0) {
- colour = *--lzw->stack_pointer;
+ colour = *--stack_pos;
if (((gif->frames[frame].transparency) &&
(colour != gif->frames[frame].transparency_index)) ||
(!gif->frames[frame].transparency)) {
@@ -1151,15 +860,13 @@ gif_internal_decode_frame(gif_animation *gif,
frame_scanline++;
}
} else {
- res = gif_next_LZW(gif->gif_data,
- gif->buffer_size,
- &gif->buffer_position);
- if (res != GIF_OK) {
+ res = lzw_decode(gif->lzw_ctx, &stack_pos);
+ if (res != LZW_OK) {
/* Unexpected end of frame, try to recover */
- if (res == GIF_END_OF_FRAME) {
+ if (res == LZW_OK_EOD) {
return_value = GIF_OK;
} else {
- return_value = res;
+ return_value = gif_error_from_lzw(res);
}
goto gif_decode_frame_exit;
}
@@ -1230,6 +937,14 @@ gif_result gif_initialise(gif_animation *gif, size_t size, unsigned char *data)
gif->buffer_size = size;
gif->gif_data = data;
+ if (gif->lzw_ctx == NULL) {
+ lzw_result res = lzw_context_create(
+ (struct lzw_ctx **)&gif->lzw_ctx);
+ if (res != LZW_OK) {
+ return gif_error_from_lzw(res);
+ }
+ }
+
/* Check for sufficient data to be a GIF (6-byte header + 7-byte
* logical screen descriptor)
*/
@@ -1448,4 +1163,7 @@ void gif_finalise(gif_animation *gif)
gif->local_colour_table = NULL;
free(gif->global_colour_table);
gif->global_colour_table = NULL;
+
+ lzw_context_destroy(gif->lzw_ctx);
+ gif->lzw_ctx = NULL;
}
diff --git a/src/lzw.c b/src/lzw.c
new file mode 100644
index 0000000..6b7156e
--- a/dev/null
+++ b/src/lzw.c
@@ -0,0 +1,372 @@
+/*
+ * This file is part of NetSurf's LibNSGIF, http://www.netsurf-browser.org/
+ * Licensed under the MIT License,
+ * http://www.opensource.org/licenses/mit-license.php
+ *
+ * Copyright 2017 Michael Drake <michael.drake@codethink.co.uk>
+ */
+
+#include <stdint.h>
+#include <stdlib.h>
+#include <stdbool.h>
+
+#include "lzw.h"
+
+/**
+ * \file
+ * \brief LZW decompression (implementation)
+ *
+ * Decoder for GIF LZW data.
+ */
+
+
+/**
+ * Context for reading LZW data.
+ *
+ * LZW data is split over multiple sub-blocks. Each sub-block has a
+ * byte at the start, which says the sub-block size, and then the data.
+ * Zero-size sub-blocks have no data, and the biggest sub-block size is
+ * 255, which means there are 255 bytes of data following the sub-block
+ * size entry.
+ *
+ * Note that an individual LZW code can be split over up to three sub-blocks.
+ */
+struct lzw_read_ctx {
+ const uint8_t *data; /**< Pointer to start of input data */
+ uint32_t data_len; /**< Input data length */
+ uint32_t data_sb_next; /**< Offset to sub-block size */
+
+ const uint8_t *sb_data; /**< Pointer to current sub-block in data */
+ uint32_t sb_bit; /**< Current bit offset in sub-block */
+ uint32_t sb_bit_count; /**< Bit count in sub-block */
+};
+
+/**
+ * LZW dictionary entry.
+ *
+ * Records in the dictionary are composed of 1 or more entries.
+ * Entries point to previous entries which can be followed to compose
+ * the complete record. To compose the record in reverse order, take
+ * the `last_value` from each entry, and move to the previous entry.
+ * If the previous_entry's index is < the current clear_code, then it
+ * is the last entry in the record.
+ */
+struct lzw_dictionary_entry {
+ uint8_t last_value; /**< Last value for record ending at entry. */
+ uint8_t first_value; /**< First value for entry's record. */
+ uint16_t previous_entry; /**< Offset in dictionary to previous entry. */
+};
+
+/**
+ * LZW decompression context.
+ */
+struct lzw_ctx {
+ /** Input reading context */
+ struct lzw_read_ctx input;
+
+ uint32_t previous_code; /**< Code read from input previously. */
+ uint32_t previous_code_first; /**< First value of previous code. */
+
+ uint32_t initial_code_size; /**< Starting LZW code size. */
+ uint32_t current_code_size; /**< Current LZW code size. */
+ uint32_t current_code_size_max; /**< Max code value for current size. */
+
+ uint32_t clear_code; /**< Special Clear code value */
+ uint32_t eoi_code; /**< Special End of Information code value */
+
+ uint32_t current_entry; /**< Next position in table to fill. */
+
+ /** Output value stack. */
+ uint8_t stack_base[1 << LZW_CODE_MAX];
+
+ /** LZW decode dictionary. Generated during decode. */
+ struct lzw_dictionary_entry table[1 << LZW_CODE_MAX];
+};
+
+
+/* Exported function, documented in lzw.h */
+lzw_result lzw_context_create(struct lzw_ctx **ctx)
+{
+ struct lzw_ctx *c = malloc(sizeof(*c));
+ if (c == NULL) {
+ return LZW_NO_MEM;
+ }
+
+ *ctx = c;
+ return LZW_OK;
+}
+
+
+/* Exported function, documented in lzw.h */
+void lzw_context_destroy(struct lzw_ctx *ctx)
+{
+ free(ctx);
+}
+
+
+/**
+ * Advance the context to the next sub-block in the input data.
+ *
+ * \param[in] ctx LZW reading context, updated on success.
+ * \return LZW_OK or LZW_OK_EOD on success, appropriate error otherwise.
+ */
+static lzw_result lzw__block_advance(struct lzw_read_ctx *ctx)
+{
+ uint32_t block_size;
+ uint32_t next_block_pos = ctx->data_sb_next;
+ const uint8_t *data_next = ctx->data + next_block_pos;
+
+ if (next_block_pos >= ctx->data_len) {
+ return LZW_NO_DATA;
+ }
+
+ block_size = *data_next;
+
+ if ((next_block_pos + block_size) >= ctx->data_len) {
+ return LZW_NO_DATA;
+ }
+
+ ctx->sb_bit = 0;
+ ctx->sb_bit_count = block_size * 8;
+
+ if (block_size == 0) {
+ ctx->data_sb_next += 1;
+ return LZW_OK_EOD;
+ }
+
+ ctx->sb_data = data_next + 1;
+ ctx->data_sb_next += block_size + 1;
+
+ return LZW_OK;
+}
+
+
+/**
+ * Get the next LZW code of given size from the raw input data.
+ *
+ * Reads codes from the input data stream coping with GIF data sub-blocks.
+ *
+ * \param[in] ctx LZW reading context, updated.
+ * \param[in] code_size Size of LZW code to get from data.
+ * \param[out] code_out Returns an LZW code on success.
+ * \return LZW_OK or LZW_OK_EOD on success, appropriate error otherwise.
+ */
+static inline lzw_result lzw__next_code(
+ struct lzw_read_ctx *ctx,
+ uint8_t code_size,
+ uint32_t *code_out)
+{
+ uint32_t code = 0;
+ uint8_t current_bit = ctx->sb_bit & 0x7;
+ uint8_t byte_advance = (current_bit + code_size) >> 3;
+
+ if (ctx->sb_bit + code_size < ctx->sb_bit_count) {
+ /* Fast path: code fully inside this sub-block */
+ const uint8_t *data = ctx->sb_data + (ctx->sb_bit >> 3);
+ switch (byte_advance) {
+ case 2: code |= data[2] << 16;
+ case 1: code |= data[1] << 8;
+ case 0: code |= data[0] << 0;
+ }
+ ctx->sb_bit += code_size;
+ } else {
+ /* Slow path: code spans sub-blocks */
+ uint8_t byte = 0;
+ uint8_t bits_remaining_0 = (code_size < (8 - current_bit)) ?
+ code_size : (8 - current_bit);
+ uint8_t bits_remaining_1 = code_size - bits_remaining_0;
+ uint8_t bits_used[3] = {
+ [0] = bits_remaining_0,
+ [1] = bits_remaining_1 < 8 ? bits_remaining_1 : 8,
+ [2] = bits_remaining_1 - 8,
+ };
+
+ while (true) {
+ const uint8_t *data = ctx->sb_data;
+ lzw_result res;
+
+ /* Get any data from end of this sub-block */
+ while (byte <= byte_advance &&
+ ctx->sb_bit < ctx->sb_bit_count) {
+ code |= data[ctx->sb_bit >> 3] << (byte << 3);
+ ctx->sb_bit += bits_used[byte];
+ byte++;
+ }
+
+ /* Check if we have all we need */
+ if (byte > byte_advance) {
+ break;
+ }
+
+ /* Move to next sub-block */
+ res = lzw__block_advance(ctx);
+ if (res != LZW_OK) {
+ return res;
+ }
+ }
+ }
+
+ *code_out = (code >> current_bit) & ((1 << code_size) - 1);
+ return LZW_OK;
+}
+
+
+/**
+ * Clear LZW code dictionary.
+ *
+ * \param[in] ctx LZW reading context, updated.
+ * \param[out] stack_pos_out Returns current stack position.
+ * \return LZW_OK or error code.
+ */
+static lzw_result lzw__clear_codes(
+ struct lzw_ctx *ctx,
+ const uint8_t ** const stack_pos_out)
+{
+ uint32_t code;
+ uint8_t *stack_pos;
+
+ /* Reset dictionary building context */
+ ctx->current_code_size = ctx->initial_code_size + 1;
+ ctx->current_code_size_max = (1 << ctx->current_code_size) - 1;;
+ ctx->current_entry = (1 << ctx->initial_code_size) + 2;
+
+ /* There might be a sequence of clear codes, so process them all */
+ do {
+ lzw_result res = lzw__next_code(&ctx->input,
+ ctx->current_code_size, &code);
+ if (res != LZW_OK) {
+ return res;
+ }
+ } while (code == ctx->clear_code);
+
+ /* The initial code must be from the initial dictionary. */
+ if (code > ctx->clear_code) {
+ return LZW_BAD_ICODE;
+ }
+
+ /* Record this initial code as "previous" code, needed during decode. */
+ ctx->previous_code = code;
+ ctx->previous_code_first = code;
+
+ /* Reset the stack, and add first non-clear code added as first item. */
+ stack_pos = ctx->stack_base;
+ *stack_pos++ = code;
+
+ *stack_pos_out = stack_pos;
+ return LZW_OK;
+}
+
+
+/* Exported function, documented in lzw.h */
+lzw_result lzw_decode_init(
+ struct lzw_ctx *ctx,
+ const uint8_t *compressed_data,
+ uint32_t compressed_data_len,
+ uint32_t compressed_data_pos,
+ uint8_t code_size,
+ const uint8_t ** const stack_base_out,
+ const uint8_t ** const stack_pos_out)
+{
+ struct lzw_dictionary_entry *table = ctx->table;
+
+ /* Initialise the input reading context */
+ ctx->input.data = compressed_data;
+ ctx->input.data_len = compressed_data_len;
+ ctx->input.data_sb_next = compressed_data_pos;
+
+ ctx->input.sb_bit = 0;
+ ctx->input.sb_bit_count = 0;
+
+ /* Initialise the dictionary building context */
+ ctx->initial_code_size = code_size;
+
+ ctx->clear_code = (1 << code_size) + 0;
+ ctx->eoi_code = (1 << code_size) + 1;
+
+ /* Initialise the standard dictionary entries */
+ for (uint32_t i = 0; i < ctx->clear_code; ++i) {
+ table[i].first_value = i;
+ table[i].last_value = i;
+ }
+
+ *stack_base_out = ctx->stack_base;
+ return lzw__clear_codes(ctx, stack_pos_out);
+}
+
+
+/* Exported function, documented in lzw.h */
+lzw_result lzw_decode(struct lzw_ctx *ctx,
+ const uint8_t ** const stack_pos_out)
+{
+ lzw_result res;
+ uint32_t code_new;
+ uint32_t code_out;
+ uint8_t last_value;
+ uint8_t *stack_pos = ctx->stack_base;
+ uint32_t clear_code = ctx->clear_code;
+ uint32_t current_entry = ctx->current_entry;
+ struct lzw_dictionary_entry * const table = ctx->table;
+
+ /* Get a new code from the input */
+ res = lzw__next_code(&ctx->input, ctx->current_code_size, &code_new);
+ if (res != LZW_OK) {
+ return res;
+ }
+
+ if (code_new == clear_code) {
+ /* Got Clear code */
+ return lzw__clear_codes(ctx, stack_pos_out);
+
+ } else if (code_new == ctx->eoi_code) {
+ /* Got End of Information code */
+ return LZW_EOI_CODE;
+ }
+
+ if (code_new > current_entry) {
+ /* Code is invalid */
+ return LZW_BAD_CODE;
+ } else if (code_new < current_entry) {
+ /* Code is in table */
+ code_out = code_new;
+ last_value = table[code_new].first_value;
+ } else {
+ /* Code not in table */
+ *stack_pos++ = ctx->previous_code_first;
+ code_out = ctx->previous_code;
+ last_value = ctx->previous_code_first;
+ }
+
+ /* Add to the dictionary, only if there's space */
+ if (current_entry < (1 << LZW_CODE_MAX)) {
+ struct lzw_dictionary_entry *entry = table + current_entry;
+ entry->last_value = last_value;
+ entry->first_value = ctx->previous_code_first;
+ entry->previous_entry = ctx->previous_code;
+ ctx->current_entry++;
+ }
+
+ /* Ensure code size is increased, if needed. */
+ if (current_entry == ctx->current_code_size_max) {
+ if (ctx->current_code_size < LZW_CODE_MAX) {
+ ctx->current_code_size++;
+ ctx->current_code_size_max =
+ (1 << ctx->current_code_size) - 1;
+ }
+ }
+
+ ctx->previous_code_first = table[code_new].first_value;
+ ctx->previous_code = code_new;
+
+ /* Put rest of data for this code on output stack.
+ * Note, in the case of "code not in table", the last entry of the
+ * current code has already been placed on the stack above. */
+ while (code_out > clear_code) {
+ struct lzw_dictionary_entry *entry = table + code_out;
+ *stack_pos++ = entry->last_value;
+ code_out = entry->previous_entry;
+ }
+ *stack_pos++ = table[code_out].last_value;
+
+ *stack_pos_out = stack_pos;
+ return LZW_OK;
+}
diff --git a/src/lzw.h b/src/lzw.h
new file mode 100644
index 0000000..385b425
--- a/dev/null
+++ b/src/lzw.h
@@ -0,0 +1,105 @@
+/*
+ * This file is part of NetSurf's LibNSGIF, http://www.netsurf-browser.org/
+ * Licensed under the MIT License,
+ * http://www.opensource.org/licenses/mit-license.php
+ *
+ * Copyright 2017 Michael Drake <michael.drake@codethink.co.uk>
+ */
+
+#ifndef LZW_H_
+#define LZW_H_
+
+/**
+ * \file
+ * \brief LZW decompression (interface)
+ *
+ * Decoder for GIF LZW data.
+ */
+
+
+/** Maximum LZW code size in bits */
+#define LZW_CODE_MAX 12
+
+
+/* Declare lzw internal context structure */
+struct lzw_ctx;
+
+
+/** LZW decoding response codes */
+typedef enum lzw_result {
+ LZW_OK, /**< Success */
+ LZW_OK_EOD, /**< Success; reached zero-length sub-block */
+ LZW_NO_MEM, /**< Error: Out of memory */
+ LZW_NO_DATA, /**< Error: Out of data */
+ LZW_EOI_CODE, /**< Error: End of Information code */
+ LZW_BAD_ICODE, /**< Error: Bad initial LZW code */
+ LZW_BAD_CODE, /**< Error: Bad LZW code */
+} lzw_result;
+
+
+/**
+ * Create an LZW decompression context.
+ *
+ * \param[out] ctx Returns an LZW decompression context. Caller owned,
+ * free with lzw_context_destroy().
+ * \return LZW_OK on success, or appropriate error code otherwise.
+ */
+lzw_result lzw_context_create(
+ struct lzw_ctx **ctx);
+
+/**
+ * Destroy an LZW decompression context.
+ *
+ * \param[in] ctx The LZW decompression context to destroy.
+ */
+void lzw_context_destroy(
+ struct lzw_ctx *ctx);
+
+/**
+ * Initialise an LZW decompression context for decoding.
+ *
+ * Caller owns neither `stack_base_out` or `stack_pos_out`.
+ *
+ * \param[in] ctx The LZW decompression context to initialise.
+ * \param[in] compressed_data The compressed data.
+ * \param[in] compressed_data_len Byte length of compressed data.
+ * \param[in] compressed_data_pos Start position in data. Must be position
+ * of a size byte at sub-block start.
+ * \param[in] code_size The initial LZW code size to use.
+ * \param[out] stack_base_out Returns base of decompressed data stack.
+ * \param[out] stack_pos_out Returns current stack position.
+ * There are `stack_pos_out - stack_base_out`
+ * current stack entries.
+ * \return LZW_OK on success, or appropriate error code otherwise.
+ */
+lzw_result lzw_decode_init(
+ struct lzw_ctx *ctx,
+ const uint8_t *compressed_data,
+ uint32_t compressed_data_len,
+ uint32_t compressed_data_pos,
+ uint8_t code_size,
+ const uint8_t ** const stack_base_out,
+ const uint8_t ** const stack_pos_out);
+
+/**
+ * Fill the LZW stack with decompressed data
+ *
+ * Ensure anything on the stack is used before calling this, as anything
+ * on the stack before this call will be trampled.
+ *
+ * Caller does not own `stack_pos_out`.
+ *
+ * \param[in] ctx LZW reading context, updated.
+ * \param[out] stack_pos_out Returns current stack position.
+ * Use with `stack_base_out` value from previous
+ * lzw_decode_init() call.
+ * There are `stack_pos_out - stack_base_out`
+ * current stack entries.
+ * \return LZW_OK on success, or appropriate error code otherwise.
+ */
+lzw_result lzw_decode(
+ struct lzw_ctx *ctx,
+ const uint8_t ** const stack_pos_out);
+
+
+#endif
diff --git a/test/decode_gif.c b/test/decode_gif.c
index aafe7f6..0ce53c7 100644
--- a/test/decode_gif.c
+++ b/test/decode_gif.c
@@ -135,19 +135,22 @@ static void warning(const char *context, gif_result code)
fprintf(stderr, "\n");
}
-static void write_ppm(FILE* fh, const char *name, gif_animation *gif)
+static void write_ppm(FILE* fh, const char *name, gif_animation *gif,
+ bool no_write)
{
unsigned int i;
gif_result code;
- fprintf(fh, "P3\n");
- fprintf(fh, "# %s\n", name);
- fprintf(fh, "# width %u \n", gif->width);
- fprintf(fh, "# height %u \n", gif->height);
- fprintf(fh, "# frame_count %u \n", gif->frame_count);
- fprintf(fh, "# frame_count_partial %u \n", gif->frame_count_partial);
- fprintf(fh, "# loop_count %u \n", gif->loop_count);
- fprintf(fh, "%u %u 256\n", gif->width, gif->height * gif->frame_count);
+ if (!no_write) {
+ fprintf(fh, "P3\n");
+ fprintf(fh, "# %s\n", name);
+ fprintf(fh, "# width %u \n", gif->width);
+ fprintf(fh, "# height %u \n", gif->height);
+ fprintf(fh, "# frame_count %u \n", gif->frame_count);
+ fprintf(fh, "# frame_count_partial %u \n", gif->frame_count_partial);
+ fprintf(fh, "# loop_count %u \n", gif->loop_count);
+ fprintf(fh, "%u %u 256\n", gif->width, gif->height * gif->frame_count);
+ }
/* decode the frames */
for (i = 0; i != gif->frame_count; i++) {
@@ -158,17 +161,19 @@ static void write_ppm(FILE* fh, const char *name, gif_animation *gif)
if (code != GIF_OK)
warning("gif_decode_frame", code);
- fprintf(fh, "# frame %u:\n", i);
- image = (unsigned char *) gif->frame_image;
- for (row = 0; row != gif->height; row++) {
- for (col = 0; col != gif->width; col++) {
- size_t z = (row * gif->width + col) * 4;
- fprintf(fh, "%u %u %u ",
- (unsigned char) image[z],
- (unsigned char) image[z + 1],
- (unsigned char) image[z + 2]);
+ if (!no_write) {
+ fprintf(fh, "# frame %u:\n", i);
+ image = (unsigned char *) gif->frame_image;
+ for (row = 0; row != gif->height; row++) {
+ for (col = 0; col != gif->width; col++) {
+ size_t z = (row * gif->width + col) * 4;
+ fprintf(fh, "%u %u %u ",
+ (unsigned char) image[z],
+ (unsigned char) image[z + 1],
+ (unsigned char) image[z + 2]);
+ }
+ fprintf(fh, "\n");
}
- fprintf(fh, "\n");
}
}
@@ -189,17 +194,28 @@ int main(int argc, char *argv[])
gif_result code;
unsigned char *data;
FILE *outf = stdout;
+ bool no_write = false;
if (argc < 2) {
fprintf(stderr, "Usage: %s image.gif [out]\n", argv[0]);
+ fprintf(stderr, "\n");
+ fprintf(stderr, "If [out] is NOWRITE, the gif will be docoded "
+ "but not output.\n");
+ fprintf(stderr, "Otherwise [out] is an output filename.\n");
+ fprintf(stderr, "When [out] is unset, output is to stdout.\n");
+
return 1;
}
if (argc > 2) {
- outf = fopen(argv[2], "w+");
- if (outf == NULL) {
- fprintf(stderr, "Unable to open %s for writing\n", argv[2]);
- return 2;
+ if (strcmp(argv[2], "NOWRITE") == 0) {
+ no_write = true;
+ } else {
+ outf = fopen(argv[2], "w+");
+ if (outf == NULL) {
+ fprintf(stderr, "Unable to open %s for writing\n", argv[2]);
+ return 2;
+ }
}
}
@@ -218,9 +234,9 @@ int main(int argc, char *argv[])
}
} while (code != GIF_OK);
- write_ppm(outf, argv[1], &gif);
+ write_ppm(outf, argv[1], &gif, no_write);
- if (argc > 2) {
+ if (argc > 2 && !no_write) {
fclose(outf);
}