AuroraMiddleware/skia2
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Add a note about (x*y+255)/256.

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BUG=skia:4117

Review URL: https://codereview.chromium.org/1312283004
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mtklein 2015-08-27 12:05:56 -07:00 committed by Commit bot
parent e01008fdbc
commit 6904d1d3f1
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src/core/Sk4px.h
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@ -103,6 +103,7 @@ public:
// May be incorrect by +-1, but is always exactly correct when *this or o is 0 or 255. // May be incorrect by +-1, but is always exactly correct when *this or o is 0 or 255.
Sk4px approxMulDiv255(const Sk16b& o) const { Sk4px approxMulDiv255(const Sk16b& o) const {
// (x*y + x) / 256 meets these criteria. (As of course does (x*y + y) / 256 by symmetry.) // (x*y + x) / 256 meets these criteria. (As of course does (x*y + y) / 256 by symmetry.)
// FYI: (x*y + 255) / 256 also meets these criteria. In my brief testing, it was slower.
return this->widenLo().addNarrowHi(*this * o); return this->widenLo().addNarrowHi(*this * o);
} }