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Implement SHSUB8 and SHSUB16 (#74)

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* Implement IR operations PackedHalvingSubS8 and PackedHalvingSubS16
This commit is contained in:
Fernando Sahmkow 2016-12-22 07:02:24 -05:00 • committed by Merry
parent 967f3cf7e1
commit 677f62dd6f
5 changed files with 95 additions and 5 deletions
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70
src/backend_x64/emit_x64.cpp
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@ -1928,6 +1928,41 @@ void EmitX64::EmitPackedHalvingSubU8(IR::Block&, IR::Inst* inst) {
// minuend now contains the desired result.
}
void EmitX64::EmitPackedHalvingSubS8(IR::Block&, IR::Inst* inst) {
IR::Value a = inst->GetArg(0);
IR::Value b = inst->GetArg(1);
Xbyak::Reg32 minuend = reg_alloc.UseDefGpr(a, inst).cvt32();
Xbyak::Reg32 subtrahend = reg_alloc.UseScratchGpr(b).cvt32();
Xbyak::Reg32 carry = reg_alloc.ScratchGpr().cvt32();
// This relies on the equality x-y == (x^y) - (((x^y)&y) << 1).
// Note that x^y always contains the LSB of the result.
// Since we want to calculate (x-y)/2, we can instead calculate ((x^y)>>1) - ((x^y)&y).
code->xor(minuend, subtrahend);
code->and(subtrahend, minuend);
code->mov(carry, minuend);
code->and(carry, 0x80808080);
code->shr(minuend, 1);
// At this point,
// minuend := (a^b) >> 1
// subtrahend := (a^b) & b
// carry := (a^b) & 0x80808080
// We must now perform a partitioned subtraction.
// We can do this because minuend contains 7 bit fields.
// We use the extra bit in minuend as a bit to borrow from; we set this bit.
// We invert this bit at the end as this tells us if that bit was borrowed from.
// We then sign extend the result into this bit.
code->or(minuend, 0x80808080);
code->sub(minuend, subtrahend);
code->xor(minuend, 0x80808080);
code->xor(minuend, carry);
}
void EmitX64::EmitPackedHalvingSubU16(IR::Block&, IR::Inst* inst) {
IR::Value a = inst->GetArg(0);
IR::Value b = inst->GetArg(1);
@ -1954,8 +1989,41 @@ void EmitX64::EmitPackedHalvingSubU16(IR::Block&, IR::Inst* inst) {
code->or(minuend, 0x80008000);
code->sub(minuend, subtrahend);
code->xor(minuend, 0x80008000);
}
// minuend now contains the desired result.
void EmitX64::EmitPackedHalvingSubS16(IR::Block&, IR::Inst* inst) {
IR::Value a = inst->GetArg(0);
IR::Value b = inst->GetArg(1);
Xbyak::Reg32 minuend = reg_alloc.UseDefGpr(a, inst).cvt32();
Xbyak::Reg32 subtrahend = reg_alloc.UseScratchGpr(b).cvt32();
Xbyak::Reg32 carry = reg_alloc.ScratchGpr().cvt32();
// This relies on the equality x-y == (x^y) - (((x^y)&y) << 1).
// Note that x^y always contains the LSB of the result.
// Since we want to calculate (x-y)/2, we can instead calculate ((x^y)>>1) - ((x^y)&y).
code->xor(minuend, subtrahend);
code->and(subtrahend, minuend);
code->mov(carry, minuend);
code->and(carry, 0x80008000);
code->shr(minuend, 1);
// At this point,
// minuend := (a^b) >> 1
// subtrahend := (a^b) & b
// carry := (a^b) & 0x80008000
// We must now perform a partitioned subtraction.
// We can do this because minuend contains 7 bit fields.
// We use the extra bit in minuend as a bit to borrow from; we set this bit.
// We invert this bit at the end as this tells us if that bit was borrowed from.
// We then sign extend the result into this bit.
code->or(minuend, 0x80008000);
code->sub(minuend, subtrahend);
code->xor(minuend, 0x80008000);
code->xor(minuend, carry);
}
static void EmitPackedOperation(BlockOfCode* code, RegAlloc& reg_alloc, IR::Inst* inst, void (Xbyak::CodeGenerator::*fn)(const Xbyak::Mmx& mmx, const Xbyak::Operand&)) {