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[libpng16] Avoid filter-selection heuristic sum calculations in cases where

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only one filter is a candidate for selection. This trades off code size (added
png_setup_*_row_only() functions) for speed.
This commit is contained in:
Glenn Randers-Pehrson 2016-06-19 18:43:35 -05:00
parent 9c04f57cab
commit 29135161d7
3 changed files with 110 additions and 7 deletions
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3
ANNOUNCE
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@ -45,6 +45,9 @@ Version 1.6.24beta02 [June 19, 2016]
implemented in 1.7), however a simple safe fix here is to chose the lowest
numbered filter in the list from png_set_filter (this only works if the
first problem is also fixed) (John Bowler).
Avoid filter-selection heuristic sum calculations in cases where only one
filter is a candidate for selection. This trades off code size (added
png_setup_*_row_only() functions) for speed.
Send comments/corrections/commendations to png-mng-implement at lists.sf.net
(subscription required; visit

3
CHANGES
View File

@ -5616,6 +5616,9 @@ Version 1.6.24beta02 [June 19, 2016]
implemented in 1.7), however a simple safe fix here is to chose the lowest
numbered filter in the list from png_set_filter (this only works if the
first problem is also fixed) (John Bowler).
Avoid filter-selection heuristic sum calculations in cases where only one
filter is a candidate for selection. This trades off code size (added
png_setup_*_row_only() functions) for speed.
Send comments/corrections/commendations to png-mng-implement at lists.sf.net
(subscription required; visit

111
pngwutil.c
View File

@ -2278,6 +2278,28 @@ png_setup_sub_row(png_structrp png_ptr, const png_uint_32 bpp,
return (sum);
}
static void /* PRIVATE */
png_setup_sub_row_only(png_structrp png_ptr, const png_uint_32 bpp,
const png_size_t row_bytes)
{
png_bytep rp, dp, lp;
png_size_t i;
png_ptr->try_row[0] = PNG_FILTER_VALUE_SUB;
for (i = 0, rp = png_ptr->row_buf + 1, dp = png_ptr->try_row + 1; i < bpp;
i++, rp++, dp++)
{
*dp = *rp;
}
for (lp = png_ptr->row_buf + 1; i < row_bytes;
i++, rp++, lp++, dp++)
{
*dp = (png_byte)(((int)*rp - (int)*lp) & 0xff);
}
}
static png_size_t /* PRIVATE */
png_setup_up_row(png_structrp png_ptr, const png_size_t row_bytes,
const png_size_t lmins)
@ -2302,6 +2324,21 @@ png_setup_up_row(png_structrp png_ptr, const png_size_t row_bytes,
return (sum);
}
static void /* PRIVATE */
png_setup_up_row_only(png_structrp png_ptr, const png_size_t row_bytes)
{
png_bytep rp, dp, pp;
png_size_t i;
png_ptr->try_row[0] = PNG_FILTER_VALUE_UP;
for (i = 0, rp = png_ptr->row_buf + 1, dp = png_ptr->try_row + 1,
pp = png_ptr->prev_row + 1; i < row_bytes;
i++, rp++, pp++, dp++)
{
*dp = (png_byte)(((int)*rp - (int)*pp) & 0xff);
}
}
static png_size_t /* PRIVATE */
png_setup_avg_row(png_structrp png_ptr, const png_uint_32 bpp,
@ -2335,6 +2372,27 @@ png_setup_avg_row(png_structrp png_ptr, const png_uint_32 bpp,
return (sum);
}
static void /* PRIVATE */
png_setup_avg_row_only(png_structrp png_ptr, const png_uint_32 bpp,
const png_size_t row_bytes)
{
png_bytep rp, dp, pp, lp;
png_uint_32 i;
png_ptr->try_row[0] = PNG_FILTER_VALUE_AVG;
for (i = 0, rp = png_ptr->row_buf + 1, dp = png_ptr->try_row + 1,
pp = png_ptr->prev_row + 1; i < bpp; i++)
{
*dp++ = (png_byte)(((int)*rp++ - ((int)*pp++ / 2)) & 0xff);
}
for (lp = png_ptr->row_buf + 1; i < row_bytes; i++)
{
*dp++ = (png_byte)(((int)*rp++ - (((int)*pp++ + (int)*lp++) / 2))
& 0xff);
}
}
static png_size_t /* PRIVATE */
png_setup_paeth_row(png_structrp png_ptr, const png_uint_32 bpp,
@ -2389,6 +2447,48 @@ png_setup_paeth_row(png_structrp png_ptr, const png_uint_32 bpp,
return (sum);
}
static void /* PRIVATE */
png_setup_paeth_row_only(png_structrp png_ptr, const png_uint_32 bpp,
const png_size_t row_bytes)
{
png_bytep rp, dp, pp, cp, lp;
png_size_t i;
png_ptr->try_row[0] = PNG_FILTER_VALUE_PAETH;
for (i = 0, rp = png_ptr->row_buf + 1, dp = png_ptr->try_row + 1,
pp = png_ptr->prev_row + 1; i < bpp; i++)
{
*dp++ = (png_byte)(((int)*rp++ - (int)*pp++) & 0xff);
}
for (lp = png_ptr->row_buf + 1, cp = png_ptr->prev_row + 1; i < row_bytes;
i++)
{
int a, b, c, pa, pb, pc, p;
b = *pp++;
c = *cp++;
a = *lp++;
p = b - c;
pc = a - c;
#ifdef PNG_USE_ABS
pa = abs(p);
pb = abs(pc);
pc = abs(p + pc);
#else
pa = p < 0 ? -p : p;
pb = pc < 0 ? -pc : pc;
pc = (p + pc) < 0 ? -(p + pc) : p + pc;
#endif
p = (pa <= pb && pa <=pc) ? a : (pb <= pc) ? b : c;
*dp++ = (png_byte)(((int)*rp++ - p) & 0xff);
}
}
#endif /* WRITE_FILTER */
void /* PRIVATE */
@ -2476,10 +2576,7 @@ png_write_find_filter(png_structrp png_ptr, png_row_infop row_info)
if (filter_to_do == PNG_FILTER_SUB)
/* It's the only filter so no testing is needed */
{
/* Passing PNG_SIZE_MAX here and below prevents the 'setup' function
* breaking out of the loop when lmins is exceeded.
*/
(void) png_setup_sub_row(png_ptr, bpp, row_bytes, PNG_SIZE_MAX);
png_setup_sub_row_only(png_ptr, bpp, row_bytes);
best_row = png_ptr->try_row;
}
@ -2505,7 +2602,7 @@ png_write_find_filter(png_structrp png_ptr, png_row_infop row_info)
/* Up filter */
if (filter_to_do == PNG_FILTER_UP)
{
(void) png_setup_up_row(png_ptr, row_bytes, PNG_SIZE_MAX);
png_setup_up_row_only(png_ptr, row_bytes);
best_row = png_ptr->try_row;
}
@ -2531,7 +2628,7 @@ png_write_find_filter(png_structrp png_ptr, png_row_infop row_info)
/* Avg filter */
if (filter_to_do == PNG_FILTER_AVG)
{
(void) png_setup_avg_row(png_ptr, bpp, row_bytes, PNG_SIZE_MAX);
png_setup_avg_row_only(png_ptr, bpp, row_bytes);
best_row = png_ptr->try_row;
}
@ -2557,7 +2654,7 @@ png_write_find_filter(png_structrp png_ptr, png_row_infop row_info)
/* Paeth filter */
if ((filter_to_do == PNG_FILTER_PAETH) != 0)
{
(void) png_setup_paeth_row(png_ptr, bpp, row_bytes, PNG_SIZE_MAX);
png_setup_paeth_row_only(png_ptr, bpp, row_bytes);
best_row = png_ptr->try_row;
}