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[libc] tweak strtof errno behavior 

When strtof/d/ld return a subnormal number they may set errno to
ERANGE. This change makes this behavior more consistent by making any
decimal number converting to a subnormal set errno to ERANGE. This
brings it in line with hexadecimals, which currently only set errno to
ERANGE if the number is truncated when converting to a subnormal.

Reviewed By: sivachandra, lntue

Differential Revision: https://reviews.llvm.org/D113626
This commit is contained in:
Michael Jones 2021-11-10 16:19:29 -08:00
parent 18da0c0a28
commit 4cdf9884b6
3 changed files with 11 additions and 5 deletions
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4
libc/src/__support/str_to_float.h
View File

@ -308,6 +308,10 @@ simpleDecimalConversion(const char *__restrict numStart,
++exp2; ++exp2;
} }
if (exp2 == 0) {
errno = ERANGE; // NOLINT
}
*outputMantissa = finalMantissa; *outputMantissa = finalMantissa;
*outputExp2 = exp2; *outputExp2 = exp2;
} }

9
libc/test/src/__support/str_to_float_test.cpp
View File

@ -206,8 +206,8 @@ TEST_F(LlvmLibcStrToFloatTest, SimpleDecimalConversion64BasicExponents) {
} }
TEST_F(LlvmLibcStrToFloatTest, SimpleDecimalConversion64BasicSubnormals) { TEST_F(LlvmLibcStrToFloatTest, SimpleDecimalConversion64BasicSubnormals) {
SimpleDecimalConversionTest<double>("1e-320", 0x7e8, 0); SimpleDecimalConversionTest<double>("1e-320", 0x7e8, 0, ERANGE);
SimpleDecimalConversionTest<double>("1e-308", 0x730d67819e8d2, 0); SimpleDecimalConversionTest<double>("1e-308", 0x730d67819e8d2, 0, ERANGE);
SimpleDecimalConversionTest<double>("2.9e-308", 0x14da6df5e4bcc8, 1); SimpleDecimalConversionTest<double>("2.9e-308", 0x14da6df5e4bcc8, 1);
} }
@ -217,7 +217,7 @@ TEST_F(LlvmLibcStrToFloatTest, SimpleDecimalConversion64SubnormalRounding) {
// but this is the shortest string that results in the maximum subnormal that // but this is the shortest string that results in the maximum subnormal that
// I found. // I found.
SimpleDecimalConversionTest<double>("2.225073858507201e-308", 0xfffffffffffff, SimpleDecimalConversionTest<double>("2.225073858507201e-308", 0xfffffffffffff,
0); 0, ERANGE);
// Same here, if you were to extend the max subnormal out for another 800 // Same here, if you were to extend the max subnormal out for another 800
// digits, incrementing any one of those digits would create a normal number. // digits, incrementing any one of those digits would create a normal number.
@ -227,7 +227,8 @@ TEST_F(LlvmLibcStrToFloatTest, SimpleDecimalConversion64SubnormalRounding) {
TEST_F(LlvmLibcStrToFloatTest, SimpleDecimalConversion32SpecificFailures) { TEST_F(LlvmLibcStrToFloatTest, SimpleDecimalConversion32SpecificFailures) {
SimpleDecimalConversionTest<float>( SimpleDecimalConversionTest<float>(
"1.4012984643248170709237295832899161312802619418765e-45", 0x1, 0); "1.4012984643248170709237295832899161312802619418765e-45", 0x1, 0,
ERANGE);
} }
TEST(LlvmLibcStrToFloatTest, SimpleDecimalConversionExtraTypes) { TEST(LlvmLibcStrToFloatTest, SimpleDecimalConversionExtraTypes) {

3
libc/test/src/stdlib/strtof_test.cpp
View File

@ -82,7 +82,8 @@ TEST_F(LlvmLibcStrToFTest, DecimalsWithRoundingProblems) {
} }
TEST_F(LlvmLibcStrToFTest, DecimalSubnormals) { TEST_F(LlvmLibcStrToFTest, DecimalSubnormals) {
runTest("1.4012984643248170709237295832899161312802619418765e-45", 55, 0x1); runTest("1.4012984643248170709237295832899161312802619418765e-45", 55, 0x1,
ERANGE);
} }
TEST_F(LlvmLibcStrToFTest, DecimalWithLongExponent) { TEST_F(LlvmLibcStrToFTest, DecimalWithLongExponent) {