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[devel] Make the 16-to-8 scaling accurate. Dividing by 256 with no rounding is

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wrong (high by one) 25% of the time. Dividing by 257 with rounding is
    wrong in 128 out of 65536 cases. Getting the right answer all the time
    without division is easy.
This commit is contained in:
John Bowler
2011-06-10 23:24:58 -05:00
committed by Glenn Randers-Pehrson
parent cc2770850a
commit b2bee3374c
12 changed files with 81 additions and 55 deletions
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4
pngwutil.c
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@@ -834,7 +834,7 @@ png_write_IHDR(png_structp png_ptr, png_uint_32 width, png_uint_32 height,
png_ptr->zlib_method = 8;
#ifdef PNG_WRITE_COMPRESSED_TEXT_SUPPORTED
#ifdef PNG_WRITE_CUSTOMIZE_ZTXT_COMPRESSION
#ifdef PNG_WRITE_CUSTOMIZE_ZTXT_COMPRESSION_SUPPORTED
if (!(png_ptr->flags & PNG_FLAG_ZTXT_CUSTOM_STRATEGY))
png_ptr->zlib_text_strategy = Z_DEFAULT_STRATEGY;
@@ -855,7 +855,7 @@ png_write_IHDR(png_structp png_ptr, png_uint_32 width, png_uint_32 height,
png_ptr->zlib_text_mem_level = png_ptr->zlib_mem_level;
png_ptr->zlib_text_window_bits = png_ptr->zlib_window_bits;
png_ptr->zlib_text_method = png_ptr->zlib_method;
#endif /* PNG_WRITE_CUSTOMIZE_ZTXT_COMPRESSION */
#endif /* PNG_WRITE_CUSTOMIZE_ZTXT_COMPRESSION_SUPPORTED */
#endif /* PNG_WRITE_COMPRESSED_TEXT_SUPPORTED */
/* Record that the compressor has not yet been initialized. */