video_core/shader: Document sanitized MUL operation
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@ -295,14 +295,22 @@ void JitShader::Compile_DestEnable(Instruction instr, Xmm src) {
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}
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void JitShader::Compile_SanitizedMul(Xmm src1, Xmm src2, Xmm scratch) {
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// 0 * inf and inf * 0 in the PICA should return 0 instead of NaN. This can be implemented by
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// checking for NaNs before and after the multiplication. If the multiplication result is NaN
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// where neither source was, this NaN was generated by a 0 * inf multiplication, and so the
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// result should be transformed to 0 to match PICA fp rules.
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// Set scratch to mask of (src1 != NaN and src2 != NaN)
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movaps(scratch, src1);
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cmpordps(scratch, src2);
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mulps(src1, src2);
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// Set src2 to mask of (result == NaN)
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movaps(src2, src1);
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cmpunordps(src2, src2);
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// Clear components where scratch != src2 (i.e. if result is NaN where neither source was NaN)
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xorps(scratch, src2);
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andps(src1, scratch);
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}
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