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Optimise safe_subtract to avoid conditionals. 

Originally committed to SVN as r2283.
This commit is contained in:
Niels Martin Hansen 2008-07-24 00:10:43 +00:00
parent 582dd39cbd
commit 316f1afb6e
1 changed files with 23 additions and 12 deletions
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35
vsfilter/subtitles/Rasterizer.cpp
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@ -861,11 +861,18 @@ static __forceinline void pixmix2_sse2(DWORD* dst, DWORD color, DWORD shapealpha
*dst = (DWORD)_mm_cvtsi128_si32(r);
}
#include <mmintrin.h>
// Calculate a-b but without risk of underflow
template<class T>
static __forceinline T safe_subtract(T a, T b)
static __forceinline DWORD safe_subtract(DWORD a, DWORD b)
{
return (b > a) ? 0 : a - b;
// What a waste of bits...
__m64 ap = _mm_cvtsi32_si64(a);
__m64 bp = _mm_cvtsi32_si64(b);
__m64 rp = _mm_subs_pu16(ap, bp);
return (DWORD)_mm_cvtsi64_si32(rp);
// Don't need an EMMS because nothing in Draw() depends on FPU
// and we EMMS at the end of Draw().
}
// For CPUID usage in Rasterizer::Draw
@ -959,19 +966,19 @@ CRect Rasterizer::Draw(SubPicDesc& spd, CRect& clipRect, byte* pAlphaMask, int x
for(int wt=0; wt<w; ++wt)
pixmix(&dst[wt], color, s[wt*2]);
}
// Not body, ie. something else (border, shadow, I guess)
// Not painting body, ie. painting border without fill in it
else
{
if(fSSE2)
for(int wt=0; wt<w; ++wt)
// It would seems src (not s here?) contains two different
// bitmaps interlaced per pixel.
// So here's using the difference between those two.
// What if the difference underflows??
// I guess src[wt*2+1] is the widened region for border
// created by CreateWidenedRegion, and thus contains
// both the fill and the border, so subtracting the fill
// from that is always safe.
// src contains two different bitmaps, interlaced per pixel.
// The first stored is the fill, the second is the widened
// fill region created by CreateWidenedRegion().
// Since we're drawing only the border, we must otain that
// by subtracting the fill from the widened region. The
// subtraction must be saturating since the widened region
// pixel value can be smaller than the fill value.
// This happens when blur edges is used.
pixmix_sse2(&dst[wt], color, safe_subtract(src[wt*2+1], src[wt*2]));
else
for(int wt=0; wt<w; ++wt)
@ -1105,5 +1112,9 @@ CRect Rasterizer::Draw(SubPicDesc& spd, CRect& clipRect, byte* pAlphaMask, int x
dst = (unsigned long *)((char *)dst + spd.pitch);
}
// Remember to EMMS!
// Rendering fails in funny ways if we don't do this.
_mm_empty();
return bbox;
}