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[libpng16] Optimized absolute value calculation in filter selection, similar to

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code in the PAETH decoder in pngrutil.c. Build with PNG_USE_ABS to use this.
This commit is contained in:
Glenn Randers-Pehrson
2016-06-29 21:52:53 -05:00
parent ed5a01d922
commit d9779744f9
3 changed files with 41 additions and 3 deletions
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32
pngwutil.c
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@@ -2262,14 +2262,22 @@ png_setup_sub_row(png_structrp png_ptr, const png_uint_32 bpp,
i++, rp++, dp++)
{
v = *dp = *rp;
#ifdef PNG_USE_ABS
sum += 128 - abs(v - 128);
#else
sum += (v < 128) ? v : 256 - v;
#endif
}
for (lp = png_ptr->row_buf + 1; i < row_bytes;
i++, rp++, lp++, dp++)
{
v = *dp = (png_byte)(((int)*rp - (int)*lp) & 0xff);
#ifdef PNG_USE_ABS
sum += 128 - abs(v - 128);
#else
sum += (v < 128) ? v : 256 - v;
#endif
if (sum > lmins) /* We are already worse, don't continue. */
break;
@@ -2294,7 +2302,11 @@ png_setup_up_row(png_structrp png_ptr, const png_size_t row_bytes,
i++, rp++, pp++, dp++)
{
v = *dp = (png_byte)(((int)*rp - (int)*pp) & 0xff);
#ifdef PNG_USE_ABS
sum += 128 - abs(v - 128);
#else
sum += (v < 128) ? v : 256 - v;
#endif
if (sum > lmins) /* We are already worse, don't continue. */
break;
@@ -2319,7 +2331,11 @@ png_setup_avg_row(png_structrp png_ptr, const png_uint_32 bpp,
{
v = *dp++ = (png_byte)(((int)*rp++ - ((int)*pp++ / 2)) & 0xff);
#ifdef PNG_USE_ABS
sum += 128 - abs(v - 128);
#else
sum += (v < 128) ? v : 256 - v;
#endif
}
for (lp = png_ptr->row_buf + 1; i < row_bytes; i++)
@@ -2327,7 +2343,11 @@ png_setup_avg_row(png_structrp png_ptr, const png_uint_32 bpp,
v = *dp++ = (png_byte)(((int)*rp++ - (((int)*pp++ + (int)*lp++) / 2))
& 0xff);
#ifdef PNG_USE_ABS
sum += 128 - abs(v - 128);
#else
sum += (v < 128) ? v : 256 - v;
#endif
if (sum > lmins) /* We are already worse, don't continue. */
break;
@@ -2352,7 +2372,11 @@ png_setup_paeth_row(png_structrp png_ptr, const png_uint_32 bpp,
{
v = *dp++ = (png_byte)(((int)*rp++ - (int)*pp++) & 0xff);
#ifdef PNG_USE_ABS
sum += 128 - abs(v - 128);
#else
sum += (v < 128) ? v : 256 - v;
#endif
}
for (lp = png_ptr->row_buf + 1, cp = png_ptr->prev_row + 1; i < row_bytes;
@@ -2381,7 +2405,11 @@ png_setup_paeth_row(png_structrp png_ptr, const png_uint_32 bpp,
v = *dp++ = (png_byte)(((int)*rp++ - p) & 0xff);
#ifdef PNG_USE_ABS
sum += 128 - abs(v - 128);
#else
sum += (v < 128) ? v : 256 - v;
#endif
if (sum > lmins) /* We are already worse, don't continue. */
break;
@@ -2465,7 +2493,11 @@ png_write_find_filter(png_structrp png_ptr, png_row_infop row_info)
for (i = 0, rp = row_buf + 1; i < row_bytes; i++, rp++)
{
v = *rp;
#ifdef PNG_USE_ABS
sum += 128 - abs(v - 128);
#else
sum += (v < 128) ? v : 256 - v;
#endif
}
}