Add limited precision floating-point conversions of log10 for 6- and 18-bit
precisions.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@56000 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/SelectionDAG/SelectionDAGBuild.cpp b/lib/CodeGen/SelectionDAG/SelectionDAGBuild.cpp
index cadfaf4..c7c4c84 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAGBuild.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAGBuild.cpp
@@ -2955,6 +2955,25 @@
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 @@
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.