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