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Set CF correctly on BLSI patch (#722)

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* Set CF correctly on BLSI patch

* Remove redundant CLC
This commit is contained in:
Paris Oplopoios 2024-09-03 20:41:22 +03:00 committed by GitHub
parent 2b191e5b70
commit 8d3a33fe7f
1 changed files with 16 additions and 1 deletions
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17
src/core/cpu_patches.cpp
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@ -307,9 +307,24 @@ static void GenerateBLSI(const ZydisDecodedOperand* operands, Xbyak::CodeGenerat
SaveRegisters(c, {scratch});
// BLSI sets CF to zero if source is zero, otherwise it sets CF to one.
Xbyak::Label set_carry, clear_carry, end;
c.mov(scratch, *src);
c.neg(scratch);
c.neg(scratch); // NEG, like BLSI, clears CF if the source is zero and sets it otherwise
c.jc(set_carry);
c.jmp(clear_carry);
c.L(set_carry);
c.and_(scratch, *src);
c.stc(); // setting/clearing carry needs to happen after the AND because that clears CF
c.jmp(end);
c.L(clear_carry);
c.and_(scratch, *src);
// We don't need to clear carry here since AND does that for us
c.L(end);
c.mov(dst, scratch);
RestoreRegisters(c, {scratch});