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[devel] Use fast integer PNG_DIVIDE_BY_255() or PNG_DIVIDE_BY_65535()

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to accomplish alpha premultiplication when PNG_READ_COMPOSITE_NODIV_SUPPORTED
is defined.  Changed "/255" to "/255.0" in background calculations to make it
clear that the 255 is used as a double (and to prevent anyone from being
tempted to use PNG_DIVIDE_BY_255() there).
This commit is contained in:
Glenn Randers-Pehrson
2009-11-24 07:26:06 -06:00
parent 2a087220dd
commit 768429bbc1
4 changed files with 54 additions and 29 deletions
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26
png.h
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@@ -1,7 +1,7 @@
/* png.h - header file for PNG reference library
*
* libpng version 1.4.0beta105 - November 22, 2009
* libpng version 1.4.0beta105 - November 24, 2009
* Copyright (c) 1998-2009 Glenn Randers-Pehrson
* (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
* (Version 0.88 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
@@ -11,7 +11,7 @@
* Authors and maintainers:
* libpng versions 0.71, May 1995, through 0.88, January 1996: Guy Schalnat
* libpng versions 0.89c, June 1996, through 0.96, May 1997: Andreas Dilger
* libpng versions 0.97, January 1998, through 1.4.0beta105 - November 22, 2009: Glenn
* libpng versions 0.97, January 1998, through 1.4.0beta105 - November 24, 2009: Glenn
* See also "Contributing Authors", below.
*
* Note about libpng version numbers:
@@ -163,7 +163,7 @@
*
* This code is released under the libpng license.
*
* libpng versions 1.2.6, August 15, 2004, through 1.4.0beta105, November 22, 2009, are
* libpng versions 1.2.6, August 15, 2004, through 1.4.0beta105, November 24, 2009, are
* Copyright (c) 2004, 2006-2007 Glenn Randers-Pehrson, and are
* distributed according to the same disclaimer and license as libpng-1.2.5
* with the following individual added to the list of Contributing Authors:
@@ -339,7 +339,7 @@
/* Version information for png.h - this should match the version in png.c */
#define PNG_LIBPNG_VER_STRING "1.4.0beta105"
#define PNG_HEADER_VERSION_STRING \
" libpng version 1.4.0beta105 - November 22, 2009\n"
" libpng version 1.4.0beta105 - November 24, 2009\n"
#define PNG_LIBPNG_VER_SONUM 14
#define PNG_LIBPNG_VER_DLLNUM 14
@@ -2474,6 +2474,15 @@ extern PNG_EXPORT(png_bytep,png_get_io_chunk_name)
(png_uint_32)(alpha)) + (png_uint_32)32768L); \
(composite) = (png_uint_16)((temp + (temp >> 16)) >> 16); }
#ifdef PNG_READ_PREMULTIPLY_ALPHA_SUPPORTED
#define PNG_DIVIDE_BY_255(v) \
((png_byte)(((png_uint_16)v + \
(((png_uint_16)v + 128) >> 8) + 128) >> 8))
#define PNG_DIVIDE_BY_65535(v) \
((png_byte)(((png_uint_32)v + \
(((png_uint_32)v + 32768L) >> 16) + 32768L) >> 16))
#endif
#else /* Standard method using integer division */
# define png_composite(composite, fg, alpha, bg) \
@@ -2486,8 +2495,17 @@ extern PNG_EXPORT(png_bytep,png_get_io_chunk_name)
(png_uint_32)(bg)*(png_uint_32)(65535L - (png_uint_32)(alpha)) + \
(png_uint_32)32767) / (png_uint_32)65535L)
#define PNG_DIVIDE_BY_255(v) (((png_uint_16)v)/255)
#define PNG_DIVIDE_BY_65535(v) ((png_uint_32)v)/65535)
#endif /* PNG_READ_COMPOSITE_NODIV_SUPPORTED */
#ifdef PNG_READ_PREMULTIPLY_ALPHA_SUPPORTED
#define PNG_8_BIT_PREMULTIPLY(color,alpha) \
PNG_DIVIDE_BY_255((color)*(alpha))
#define PNG_16_BIT_PREMULTIPLY(color,alpha)\
PNG_DIVIDE_BY_65535((color)*(alpha))
#endif
#ifdef PNG_USE_READ_MACROS
/* Inline macros to do direct reads of bytes from the input buffer.
* The png_get_int_32() routine assumes we are using two's complement