+static SDValue getLimitedPrecisionExp2(SDValue t0, SDLoc dl,
+ SelectionDAG &DAG) {
+ // IntegerPartOfX = ((int32_t)(t0);
+ SDValue IntegerPartOfX = DAG.getNode(ISD::FP_TO_SINT, dl, MVT::i32, t0);
+
+ // FractionalPartOfX = t0 - (float)IntegerPartOfX;
+ SDValue t1 = DAG.getNode(ISD::SINT_TO_FP, dl, MVT::f32, IntegerPartOfX);
+ SDValue X = DAG.getNode(ISD::FSUB, dl, MVT::f32, t0, t1);
+
+ // IntegerPartOfX <<= 23;
+ IntegerPartOfX = DAG.getNode(
+ ISD::SHL, dl, MVT::i32, IntegerPartOfX,
+ DAG.getConstant(23, DAG.getTargetLoweringInfo().getPointerTy()));
+
+ SDValue TwoToFractionalPartOfX;
+ if (LimitFloatPrecision <= 6) {
+ // For floating-point precision of 6:
+ //
+ // TwoToFractionalPartOfX =
+ // 0.997535578f +
+ // (0.735607626f + 0.252464424f * x) * x;
+ //
+ // error 0.0144103317, which is 6 bits
+ SDValue t2 = DAG.getNode(ISD::FMUL, dl, MVT::f32, X,
+ getF32Constant(DAG, 0x3e814304));
+ SDValue t3 = DAG.getNode(ISD::FADD, dl, MVT::f32, t2,
+ getF32Constant(DAG, 0x3f3c50c8));
+ SDValue t4 = DAG.getNode(ISD::FMUL, dl, MVT::f32, t3, X);
+ TwoToFractionalPartOfX = DAG.getNode(ISD::FADD, dl, MVT::f32, t4,
+ getF32Constant(DAG, 0x3f7f5e7e));
+ } else if (LimitFloatPrecision <= 12) {
+ // For floating-point precision of 12:
+ //
+ // TwoToFractionalPartOfX =
+ // 0.999892986f +
+ // (0.696457318f +
+ // (0.224338339f + 0.792043434e-1f * x) * x) * x;
+ //
+ // error 0.000107046256, which is 13 to 14 bits
+ SDValue t2 = DAG.getNode(ISD::FMUL, dl, MVT::f32, X,
+ getF32Constant(DAG, 0x3da235e3));
+ SDValue t3 = DAG.getNode(ISD::FADD, dl, MVT::f32, t2,
+ getF32Constant(DAG, 0x3e65b8f3));
+ SDValue t4 = DAG.getNode(ISD::FMUL, dl, MVT::f32, t3, X);
+ SDValue t5 = DAG.getNode(ISD::FADD, dl, MVT::f32, t4,
+ getF32Constant(DAG, 0x3f324b07));
+ SDValue t6 = DAG.getNode(ISD::FMUL, dl, MVT::f32, t5, X);
+ TwoToFractionalPartOfX = DAG.getNode(ISD::FADD, dl, MVT::f32, t6,
+ getF32Constant(DAG, 0x3f7ff8fd));
+ } else { // LimitFloatPrecision <= 18
+ // For floating-point precision of 18:
+ //
+ // TwoToFractionalPartOfX =
+ // 0.999999982f +
+ // (0.693148872f +
+ // (0.240227044f +
+ // (0.554906021e-1f +
+ // (0.961591928e-2f +
+ // (0.136028312e-2f + 0.157059148e-3f *x)*x)*x)*x)*x)*x;
+ // error 2.47208000*10^(-7), which is better than 18 bits
+ SDValue t2 = DAG.getNode(ISD::FMUL, dl, MVT::f32, X,
+ getF32Constant(DAG, 0x3924b03e));
+ SDValue t3 = DAG.getNode(ISD::FADD, dl, MVT::f32, t2,
+ getF32Constant(DAG, 0x3ab24b87));
+ SDValue t4 = DAG.getNode(ISD::FMUL, dl, MVT::f32, t3, X);
+ SDValue t5 = DAG.getNode(ISD::FADD, dl, MVT::f32, t4,
+ getF32Constant(DAG, 0x3c1d8c17));
+ SDValue t6 = DAG.getNode(ISD::FMUL, dl, MVT::f32, t5, X);
+ SDValue t7 = DAG.getNode(ISD::FADD, dl, MVT::f32, t6,
+ getF32Constant(DAG, 0x3d634a1d));
+ SDValue t8 = DAG.getNode(ISD::FMUL, dl, MVT::f32, t7, X);
+ SDValue t9 = DAG.getNode(ISD::FADD, dl, MVT::f32, t8,
+ getF32Constant(DAG, 0x3e75fe14));
+ SDValue t10 = DAG.getNode(ISD::FMUL, dl, MVT::f32, t9, X);
+ SDValue t11 = DAG.getNode(ISD::FADD, dl, MVT::f32, t10,
+ getF32Constant(DAG, 0x3f317234));
+ SDValue t12 = DAG.getNode(ISD::FMUL, dl, MVT::f32, t11, X);
+ TwoToFractionalPartOfX = DAG.getNode(ISD::FADD, dl, MVT::f32, t12,
+ getF32Constant(DAG, 0x3f800000));
+ }
+
+ // Add the exponent into the result in integer domain.
+ SDValue t13 = DAG.getNode(ISD::BITCAST, dl, MVT::i32, TwoToFractionalPartOfX);
+ return DAG.getNode(ISD::BITCAST, dl, MVT::f32,
+ DAG.getNode(ISD::ADD, dl, MVT::i32, t13, IntegerPartOfX));
+}
+