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CNTLZ: Invert the result using xor rather than subtraction

This commit is contained in:
Dr. Chat 2016-08-01 13:24:39 -05:00
parent ff57d79793
commit 22794902f3
1 changed files with 4 additions and 16 deletions
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20
src/xenia/cpu/backend/x64/x64_sequences.cc
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@ -6264,11 +6264,8 @@ struct CNTLZ_I8 : Sequence<CNTLZ_I8, I<OPCODE_CNTLZ, I8Op, I8Op>> {
e.bsr(i.dest, i.src1);
e.jz(jz); // Jump if zero
// sub: $1 = $1 - $2
// Invert the result (7 - i.dest)
e.mov(e.eax, 7);
e.sub(e.eax, i.dest);
e.mov(i.dest, e.eax);
e.xor_(i.dest, 0x7);
e.jmp(jend); // Jmp to end
// src1 was zero, so write 8 to the dest reg
@ -6295,11 +6292,8 @@ struct CNTLZ_I16 : Sequence<CNTLZ_I16, I<OPCODE_CNTLZ, I8Op, I16Op>> {
e.bsr(i.dest, i.src1);
e.jz(jz); // Jump if zero
// sub: $1 = $1 - $2
// Invert the result (15 - i.dest)
e.mov(e.eax, 15);
e.sub(e.eax, i.dest);
e.mov(i.dest, e.eax);
e.xor_(i.dest, 0xF);
e.jmp(jend); // Jmp to end
// src1 was zero, so write 16 to the dest reg
@ -6325,11 +6319,8 @@ struct CNTLZ_I32 : Sequence<CNTLZ_I32, I<OPCODE_CNTLZ, I8Op, I32Op>> {
e.bsr(i.dest, i.src1);
e.jz(jz); // Jump if zero
// sub: $1 = $1 - $2
// Invert the result (31 - i.dest)
e.mov(e.eax, 31);
e.sub(e.eax, i.dest);
e.mov(i.dest, e.eax);
e.xor_(i.dest, 0x1F);
e.jmp(jend); // Jmp to end
// src1 was zero, so write 32 to the dest reg
@ -6355,11 +6346,8 @@ struct CNTLZ_I64 : Sequence<CNTLZ_I64, I<OPCODE_CNTLZ, I8Op, I64Op>> {
e.bsr(i.dest, i.src1);
e.jz(jz); // Jump if zero
// sub: $1 = $1 - $2
// Invert the result (63 - i.dest)
e.mov(e.rax, 63);
e.sub(e.rax, i.dest);
e.mov(i.dest, e.rax);
e.xor_(i.dest, 0x3F);
e.jmp(jend); // Jmp to end
// src1 was zero, so write 64 to the dest reg