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[libc] Fix a bug in MPFRUtils making ULP values off by 2^(-mantissaWidth).

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Fix a bug in MPFRUtils making ULP values off by 2^(-mantissaWidth) and incorrect eps for denormal numbers.

Differential Revision: https://reviews.llvm.org/D114878
This commit is contained in:
Tue Ly 2021-12-01 10:24:57 -05:00
parent 97e921c81f
commit 32568fc95e
1 changed files with 20 additions and 3 deletions
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23
libc/utils/MPFRWrapper/MPFRUtils.cpp
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@ -312,11 +312,19 @@ public:
int thisExponent = fputil::FPBits<T>(thisAsT).getExponent();
int inputExponent = fputil::FPBits<T>(input).getExponent();
// Adjust the exponents for denormal numbers.
if (fputil::FPBits<T>(thisAsT).getUnbiasedExponent() == 0)
++thisExponent;
if (fputil::FPBits<T>(input).getUnbiasedExponent() == 0)
++inputExponent;
if (thisAsT * input < 0 || thisExponent == inputExponent) {
MPFRNumber inputMPFR(input);
mpfr_sub(inputMPFR.value, value, inputMPFR.value, MPFR_RNDN);
mpfr_abs(inputMPFR.value, inputMPFR.value, MPFR_RNDN);
mpfr_mul_2si(inputMPFR.value, inputMPFR.value, -thisExponent, MPFR_RNDN);
mpfr_mul_2si(inputMPFR.value, inputMPFR.value,
-thisExponent + int(fputil::MantissaWidth<T>::value),
MPFR_RNDN);
return inputMPFR.as<double>();
}
@ -329,6 +337,11 @@ public:
T max = thisAsT > input ? thisAsT : input;
int minExponent = fputil::FPBits<T>(min).getExponent();
int maxExponent = fputil::FPBits<T>(max).getExponent();
// Adjust the exponents for denormal numbers.
if (fputil::FPBits<T>(min).getUnbiasedExponent() == 0)
++minExponent;
if (fputil::FPBits<T>(max).getUnbiasedExponent() == 0)
++maxExponent;
MPFRNumber minMPFR(min);
MPFRNumber maxMPFR(max);
@ -337,10 +350,14 @@ public:
mpfr_mul_2si(pivot.value, pivot.value, maxExponent, MPFR_RNDN);
mpfr_sub(minMPFR.value, pivot.value, minMPFR.value, MPFR_RNDN);
mpfr_mul_2si(minMPFR.value, minMPFR.value, -minExponent, MPFR_RNDN);
mpfr_mul_2si(minMPFR.value, minMPFR.value,
-minExponent + int(fputil::MantissaWidth<T>::value),
MPFR_RNDN);
mpfr_sub(maxMPFR.value, maxMPFR.value, pivot.value, MPFR_RNDN);
mpfr_mul_2si(maxMPFR.value, maxMPFR.value, -maxExponent, MPFR_RNDN);
mpfr_mul_2si(maxMPFR.value, maxMPFR.value,
-maxExponent + int(fputil::MantissaWidth<T>::value),
MPFR_RNDN);
mpfr_add(minMPFR.value, minMPFR.value, maxMPFR.value, MPFR_RNDN);
return minMPFR.as<double>();