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[devel] Optimize the zlib CMF byte in non-IDAT compressed chunks

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This commit is contained in:
Glenn Randers-Pehrson 2011-04-02 08:26:42 -05:00
parent e99107b1aa
commit 6785856858
3 changed files with 72 additions and 4 deletions
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1
ANNOUNCE
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@ -36,6 +36,7 @@ Version 1.5.3beta02 [April 2, 2011]
Only compile the new zlib re-initializing code when text or iCCP is
supported, using PNG_WRITE_COMPRESSED_TEXT_SUPPORTED macro.
Improved the optimization of the zlib CMF byte (see libpng-1.2.6beta03).
Optimize the zlib CMF byte in non-IDAT compressed chunks
Send comments/corrections/commendations to png-mng-implement at lists.sf.net:
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1
CHANGES
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@ -3297,6 +3297,7 @@ Version 1.5.3beta02 [April 2, 2011]
Only compile the new zlib re-initializing code when text or iCCP is
supported, using PNG_WRITE_COMPRESSED_TEXT_SUPPORTED macro.
Improved the optimization of the zlib CMF byte (see libpng-1.2.6beta03).
Optimize the zlib CMF byte in non-IDAT compressed chunks
Send comments/corrections/commendations to png-mng-implement at lists.sf.net
(subscription required; visit

74
pngwutil.c
View File

@ -220,13 +220,12 @@ png_text_compress(png_structp png_ptr,
comp->max_output_ptr = 0;
comp->output_ptr = NULL;
comp->input = NULL;
comp->input_len = 0;
comp->input_len = text_len;
/* We may just want to pass the text right through */
if (compression == PNG_TEXT_COMPRESSION_NONE)
{
comp->input = (png_const_bytep)text;
comp->input_len = text_len;
return((int)text_len);
}
@ -288,7 +287,6 @@ png_text_compress(png_structp png_ptr,
}
/* Set up the compression buffers */
/* TODO: the following cast hides a potential overflow problem. */
png_ptr->zstream.avail_in = (uInt)text_len;
@ -451,6 +449,69 @@ png_write_compressed_data_out(png_structp png_ptr, compression_state *comp)
return;
}
#if 1 /* For testing */
if (comp->input_len >= 2 && comp->input_len < 16384)
{
unsigned int z_cmf; /* zlib compression method and flags */
/* Optimize the CMF field in the zlib stream. This hack of the zlib
* stream is compliant to the stream specification.
*/
if (comp->num_output_ptr)
z_cmf = comp->output_ptr[0][0];
else
z_cmf = png_ptr->zbuf[0];
if ((z_cmf & 0x0f) == 8 && (z_cmf & 0xf0) <= 0x70)
{
unsigned int z_cinfo;
unsigned int half_z_window_size;
png_uint_32 uncompressed_idat_size = comp->input_len;
z_cinfo = z_cmf >> 4;
half_z_window_size = 1 << (z_cinfo + 7);
while (uncompressed_idat_size <= half_z_window_size &&
half_z_window_size >= 256)
{
z_cinfo--;
half_z_window_size >>= 1;
}
z_cmf = (z_cmf & 0x0f) | (z_cinfo << 4);
if (comp->num_output_ptr)
{
if (comp->output_ptr[0][0] != z_cmf)
{
int tmp;
comp->output_ptr[0][0] = (png_byte)z_cmf;
tmp = comp->output_ptr[0][1] & 0xe0;
tmp += 0x1f - ((z_cmf << 8) + tmp) % 0x1f;
comp->output_ptr[0][1] = (png_byte)tmp;
}
}
else
{
int tmp;
png_ptr->zbuf[0] = (png_byte)z_cmf;
tmp = png_ptr->zbuf[1] & 0xe0;
tmp += 0x1f - ((z_cmf << 8) + tmp) % 0x1f;
png_ptr->zbuf[1] = (png_byte)tmp;
}
}
else
png_error(png_ptr,
"Invalid zlib compression method or flags in non-IDAT chunk");
}
#endif
/* Write saved output buffers, if any */
for (i = 0; i < comp->num_output_ptr; i++)
{
@ -842,7 +903,8 @@ png_write_IDAT(png_structp png_ptr, png_bytep data, png_size_t length)
/* Compute the maximum possible length of the datastream */
/* Number of pixels, plus for each row a filter byte and possible
* padding byte
* and possibly a padding byte, so increase the maximum
* size to account for these.
*/
unsigned int z_cinfo;
unsigned int half_z_window_size;
@ -1013,7 +1075,10 @@ png_write_iCCP(png_structp png_ptr, png_const_charp name, int compression_type,
(png_size_t)(name_len + 2));
if (profile_len)
{
comp.input_len = profile_len;
png_write_compressed_data_out(png_ptr, &comp);
}
png_write_chunk_end(png_ptr);
png_free(png_ptr, new_name);
@ -1594,6 +1659,7 @@ png_write_zTXt(png_structp png_ptr, png_const_charp key, png_const_charp text,
png_write_chunk_data(png_ptr, &buf, (png_size_t)1);
/* Write the compressed data */
comp.input_len = text_len;
png_write_compressed_data_out(png_ptr, &comp);
/* Close the chunk */