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[devel] Improved the optimization of the zlib CMF byte

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(see libpng-1.2.6beta03).
This commit is contained in:
Glenn Randers-Pehrson
2011-04-01 22:10:41 -05:00
parent 65a24d0638
commit c3b3240a03
3 changed files with 18 additions and 6 deletions
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16
pngwutil.c
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@@ -839,13 +839,23 @@ png_write_IDAT(png_structp png_ptr, png_bytep data, png_size_t length)
if (length >= 2 &&
png_ptr->height < 16384 && png_ptr->width < 16384)
{
/* Compute the maximum possible length of the datastream
*
* To do: verify that this works with interlaced files
/* Compute the maximum possible length of the datastream */
/* Number of pixels, plus for each row a filter byte and possible
* padding byte
*/
png_uint_32 uncompressed_idat_size = png_ptr->height *
((png_ptr->width *
png_ptr->channels * png_ptr->bit_depth + 15) >> 3);
/* If it's interlaced, each block of 8 rows is sent as up to
* 14 rows, i.e., 6 additional rows, each with a filter byte
* and possibly a padding byte
*/
if (png_ptr->interlaced)
uncompressed_idat_size += ((png_ptr->height + 7)/8) *
(png_ptr->bit_depth < 8 ? 12 : 6);
unsigned int z_cinfo = z_cmf >> 4;
unsigned int half_z_window_size = 1 << (z_cinfo + 7);
while (uncompressed_idat_size <= half_z_window_size &&