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[libpng15] Optimized png_combine_row() when rows are aligned This gains a

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small percentage for 16-bit and 32-bit pixels in the typical case where the
output row buffers are appropriately aligned. The optimization was not
previously possible because the png_struct buffer was always misaligned.
This commit is contained in:
John Bowler 2011-10-07 18:36:37 -05:00 committed by Glenn Randers-Pehrson
parent ac8375d000
commit 8be28e3eb6
3 changed files with 24 additions and 11 deletions
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4
ANNOUNCE
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@ -64,6 +64,10 @@ Version 1.5.6beta05 [October 7, 2011]
a bug in the code that attempted to align it; the code needs to subtract
one from the pointer to take account of the filter byte prepended to
each row.
Optimized png_combine_row() when rows are aligned This gains a small
percentage for 16-bit and 32-bit pixels in the typical case where the
output row buffers are appropriately aligned. The optimization was not
previously possible because the png_struct buffer was always misaligned.
Send comments/corrections/commendations to png-mng-implement at lists.sf.net:
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4
CHANGES
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@ -3625,6 +3625,10 @@ Version 1.5.6beta05 [October 7, 2011]
a bug in the code that attempted to align it; the code needs to subtract
one from the pointer to take account of the filter byte prepended to
each row.
Optimized png_combine_row() when rows are aligned This gains a small
percentage for 16-bit and 32-bit pixels in the typical case where the
output row buffers are appropriately aligned. The optimization was not
previously possible because the png_struct buffer was always misaligned.
Send comments/corrections/commendations to png-mng-implement at lists.sf.net
(subscription required; visit

27
pngrutil.c
View File

@ -2931,12 +2931,13 @@ png_combine_row(png_structp png_ptr, png_bytep dp, int display)
/* This is a common optimization for 2 and 4 byte pixels, for other
* values rely on the toolchain memcpy being optimized.
*
* TBD: this should use png_isaligned, but currently something isn't
* aligned (NOTE: to be investigated in a really serious fashion.)
*/
else if (pixel_depth == 2)
else if (pixel_depth == sizeof (png_uint_16) &&
png_isaligned(sp, png_uint_16) && png_isaligned(dp, png_uint_16))
{
png_uint_16p dp16 = (png_uint_16p)dp;
png_uint_16p sp16 = (png_uint_16p)sp;
do
{
m >>= 1;
@ -2945,16 +2946,20 @@ png_combine_row(png_structp png_ptr, png_bytep dp, int display)
m = mask;
if (m & 1)
dp[0] = sp[0], dp[1] = sp[1];
*dp16 = *sp16;
dp += 2;
sp += 2;
++dp16;
++sp16;
}
while (--row_width > 0);
}
else if (pixel_depth == 4) /* as above, not optimal */
else if (pixel_depth == sizeof (png_uint_32) &&
png_isaligned(sp, png_uint_32) && png_isaligned(dp, png_uint_32))
{
png_uint_32p dp32 = (png_uint_32p)dp;
png_uint_32p sp32 = (png_uint_32p)sp;
do
{
m >>= 1;
@ -2963,10 +2968,10 @@ png_combine_row(png_structp png_ptr, png_bytep dp, int display)
m = mask;
if (m & 1)
dp[0] = sp[0], dp[1] = sp[1], dp[2] = sp[2], dp[3] = sp[3];
*dp32 = *sp32;
dp += 4;
sp += 4;
++dp32;
++sp32;
}
while (--row_width > 0);
}