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authorVincent Sanders <vince@kyllikki.org>2017-01-27 18:49:35 (GMT)
committer Vincent Sanders <vince@kyllikki.org>2017-01-27 18:49:35 (GMT)
commitaa6d8064c05f5a45132b154c266b5e2360a84dff (patch)
tree74bd08949b1d7968a67e0748e52d7cbdd6ac4f5b
parent5c5ae3e63a28b5222874017f7ec12d62403063bb (diff)
downloadlibnsgif-aa6d8064c05f5a45132b154c266b5e2360a84dff.tar.gz
libnsgif-aa6d8064c05f5a45132b154c266b5e2360a84dff.tar.bz2
make the mast table read only data in the only place it is used
-rw-r--r--src/libnsgif.c41
1 files changed, 31 insertions, 10 deletions
diff --git a/src/libnsgif.c b/src/libnsgif.c
index dc2aabb..b6d69e4 100644
--- a/src/libnsgif.c
+++ b/src/libnsgif.c
@@ -69,7 +69,6 @@
struct lzw_s {
unsigned char buf[4];
unsigned char *direct;
- int maskTbl[16];
int table[2][(1 << GIF_MAX_LZW)];
unsigned char stack[(1 << GIF_MAX_LZW) * 2];
unsigned char *stack_pointer;
@@ -95,20 +94,28 @@ struct lzw_s {
* each image which would use an extra 10Kb or so per GIF.
*/
static struct lzw_s lzw_params = {
- .maskTbl = {
- 0x0000, 0x0001, 0x0003, 0x0007, 0x000f, 0x001f, 0x003f, 0x007f,
- 0x00ff, 0x01ff, 0x03ff, 0x07ff, 0x0fff, 0x1fff, 0x3fff, 0x7fff
- },
.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 gif The GIF context
+ * \param code_size The number of bitsin the current LZW code
+ * \return The next code to process or error return code
+ */
static int gif_next_code(gif_animation *gif, int code_size)
{
int i, j, end, count, ret;
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) {
@@ -123,10 +130,13 @@ static int gif_next_code(gif_animation *gif, int code_size)
if (gif->buffer_position >= gif->buffer_size) {
return GIF_INSUFFICIENT_FRAME_DATA;
}
- lzw->zero_data_block = ((count = lzw->direct[0]) == 0);
+
+ count = lzw->direct[0];
+ lzw->zero_data_block = (count == 0);
if ((gif->buffer_position + count) >= gif->buffer_size) {
return GIF_INSUFFICIENT_FRAME_DATA;
}
+
if (count == 0) {
lzw->get_done = true;
} else {
@@ -161,14 +171,18 @@ static int gif_next_code(gif_animation *gif, int code_size)
ret |= (b[i + 2] << 16);
}
}
- ret = (ret >> (lzw->curbit % 8)) & lzw->maskTbl[code_size];
+ ret = (ret >> (lzw->curbit % 8)) & maskTbl[code_size];
lzw->curbit += code_size;
+
return ret;
}
/**
* Clear LZW code dictionary
+ *
+ * \param gif The GIF context.
+ * \return GIF_OK or error code.
*/
static gif_result gif_clear_codes_LZW(gif_animation *gif)
{
@@ -207,6 +221,12 @@ static gif_result gif_clear_codes_LZW(gif_animation *gif)
}
+/**
+ * fill the LZW stack with decompressed data
+ *
+ * \param gif The GIF context.
+ * \return true on sucessful decode of the next LZW code else false.
+ */
static bool gif_next_LZW(gif_animation *gif)
{
int code, incode;
@@ -256,7 +276,7 @@ static bool gif_next_LZW(gif_animation *gif)
/* The following loop is the most important in the GIF decoding cycle
* as every single pixel passes through it.
*
- * Note: our lzw->stack is always big enough to hold a complete decompressed
+ * Note: our stack is always big enough to hold a complete decompressed
* chunk.
*/
while (code >= lzw->clear_code) {
@@ -291,7 +311,8 @@ static bool gif_next_LZW(gif_animation *gif)
}
*lzw->stack_pointer++ = lzw->firstcode = lzw->table[1][code];
- if ((code = lzw->max_code) < (1 << GIF_MAX_LZW)) {
+ 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;