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Add limited precision floating-point conversions of log10 for 6- and 18-bit

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precisions.

llvm-svn: 56000
This commit is contained in:
Bill Wendling 2008-09-09 18:42:23 +00:00
parent 88053b82e5
commit 727b25981a
1 changed files with 56 additions and 5 deletions
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61
lib/CodeGen/SelectionDAG/SelectionDAGBuild.cpp
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@ -2955,6 +2955,25 @@ SelectionDAGLowering::visitLog10(CallInst &I) {
SDValue X = DAG.getNode(ISD::BIT_CONVERT, MVT::f32, t5);
if (LimitFloatPrecision <= 6) {
// For floating-point precision of 6:
//
// Log10ofMantissa =
// -0.50419619f +
// (0.60948995f - 0.10380950f * x) * x;
//
// error 0.0014886165, which is 6 bits
SDValue t6 = DAG.getNode(ISD::FMUL, MVT::f32, X,
DAG.getConstantFP(APFloat(
APInt(32, 0xbdd49a13)), MVT::f32));
SDValue t7 = DAG.getNode(ISD::FADD, MVT::f32, t6,
DAG.getConstantFP(APFloat(
APInt(32, 0x3f1c0789)), MVT::f32));
SDValue t8 = DAG.getNode(ISD::FMUL, MVT::f32, t7, X);
SDValue Log10ofMantissa = DAG.getNode(ISD::FSUB, MVT::f32, t8,
DAG.getConstantFP(APFloat(
APInt(32, 0x3f011300)), MVT::f32));
result = DAG.getNode(ISD::FADD, MVT::f32, LogOfExponent, Log10ofMantissa);
} else if (LimitFloatPrecision > 6 && LimitFloatPrecision <= 12) {
// For floating-point precision of 12:
//
@ -2975,14 +2994,46 @@ SelectionDAGLowering::visitLog10(CallInst &I) {
DAG.getConstantFP(APFloat(
APInt(32, 0x3f6ae232)), MVT::f32));
SDValue t10 = DAG.getNode(ISD::FMUL, MVT::f32, t9, X);
SDValue t11 = DAG.getNode(ISD::FSUB, MVT::f32, t10,
DAG.getConstantFP(APFloat(
APInt(32, 0x3f25f7c3)), MVT::f32));
SDValue Log10ofMantissa = DAG.getNode(ISD::FP_ROUND, MVT::f32, t11,
DAG.getConstant(0, MVT::i32));
SDValue Log10ofMantissa = DAG.getNode(ISD::FSUB, MVT::f32, t10,
DAG.getConstantFP(APFloat(
APInt(32, 0x3f25f7c3)), MVT::f32));
result = DAG.getNode(ISD::FADD, MVT::f32, LogOfExponent, Log10ofMantissa);
} else { // LimitFloatPrecision > 12 && LimitFloatPrecision <= 18
// For floating-point precision of 18:
//
// Log10ofMantissa =
// -0.84299375f +
// (1.5327582f +
// (-1.0688956f +
// (0.49102474f +
// (-0.12539807f + 0.13508273e-1f * x) * x) * x) * x) * x;
//
// error 0.0000037995730, which is better than 18 bits
SDValue t6 = DAG.getNode(ISD::FMUL, MVT::f32, X,
DAG.getConstantFP(APFloat(
APInt(32, 0x3c5d51ce)), MVT::f32));
SDValue t7 = DAG.getNode(ISD::FSUB, MVT::f32, t6,
DAG.getConstantFP(APFloat(
APInt(32, 0x3e00685a)), MVT::f32));
SDValue t8 = DAG.getNode(ISD::FMUL, MVT::f32, t7, X);
SDValue t9 = DAG.getNode(ISD::FADD, MVT::f32, t8,
DAG.getConstantFP(APFloat(
APInt(32, 0x3efb6798)), MVT::f32));
SDValue t10 = DAG.getNode(ISD::FMUL, MVT::f32, t9, X);
SDValue t11 = DAG.getNode(ISD::FSUB, MVT::f32, t10,
DAG.getConstantFP(APFloat(
APInt(32, 0x3f88d192)), MVT::f32));
SDValue t12 = DAG.getNode(ISD::FMUL, MVT::f32, t11, X);
SDValue t13 = DAG.getNode(ISD::FADD, MVT::f32, t12,
DAG.getConstantFP(APFloat(
APInt(32, 0x3fc4316c)), MVT::f32));
SDValue t14 = DAG.getNode(ISD::FMUL, MVT::f32, t13, X);
SDValue Log10ofMantissa = DAG.getNode(ISD::FSUB, MVT::f32, t14,
DAG.getConstantFP(APFloat(
APInt(32, 0x3f57ce70)), MVT::f32));
result = DAG.getNode(ISD::FADD, MVT::f32, LogOfExponent, Log10ofMantissa);
}
} else {
// No special expansion.