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Merge pull request #186 from leni536/negative_zero_clang

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Fix parsing -0 on clang in non-nearest rounding modes.
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Daniel Lemire 2023-03-25 16:03:13 -04:00 committed by GitHub
commit c09c855ea6
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2 changed files with 48 additions and 1 deletions
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2
include/fast_float/parse_number.h
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@ -191,7 +191,7 @@ from_chars_result from_chars_advanced(const char *first, const char *last,
#if defined(__clang__) #if defined(__clang__)
// Clang may map 0 to -0.0 when fegetround() == FE_DOWNWARD // Clang may map 0 to -0.0 when fegetround() == FE_DOWNWARD
if(pns.mantissa == 0) { if(pns.mantissa == 0) {
value = 0; value = pns.negative ? -0. : 0.;
return answer; return answer;
} }
#endif #endif

47
tests/basictest.cpp
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@ -184,6 +184,53 @@ TEST_CASE("parse_zero") {
CHECK(float64_parsed == 0); CHECK(float64_parsed == 0);
} }
TEST_CASE("parse_negative_zero") {
//
// If this function fails, we may be left in a non-standard rounding state.
//
const char * negative_zero = "-0";
uint64_t float64_parsed;
double f = -0.;
::memcpy(&float64_parsed, &f, sizeof(f));
CHECK(float64_parsed == 0x8000'0000'0000'0000);
fesetround(FE_UPWARD);
auto r1 = fast_float::from_chars(negative_zero, negative_zero + 2, f);
CHECK(r1.ec == std::errc());
std::cout << "FE_UPWARD parsed negative zero as " << iHexAndDec(f) << std::endl;
CHECK(f == 0);
::memcpy(&float64_parsed, &f, sizeof(f));
std::cout << "double as uint64_t is " << float64_parsed << std::endl;
CHECK(float64_parsed == 0x8000'0000'0000'0000);
fesetround(FE_TOWARDZERO);
auto r2 = fast_float::from_chars(negative_zero, negative_zero + 2, f);
CHECK(r2.ec == std::errc());
std::cout << "FE_TOWARDZERO parsed negative zero as " << iHexAndDec(f) << std::endl;
CHECK(f == 0);
::memcpy(&float64_parsed, &f, sizeof(f));
std::cout << "double as uint64_t is " << float64_parsed << std::endl;
CHECK(float64_parsed == 0x8000'0000'0000'0000);
fesetround(FE_DOWNWARD);
auto r3 = fast_float::from_chars(negative_zero, negative_zero + 2, f);
CHECK(r3.ec == std::errc());
std::cout << "FE_DOWNWARD parsed negative zero as " << iHexAndDec(f) << std::endl;
CHECK(f == 0);
::memcpy(&float64_parsed, &f, sizeof(f));
std::cout << "double as uint64_t is " << float64_parsed << std::endl;
CHECK(float64_parsed == 0x8000'0000'0000'0000);
fesetround(FE_TONEAREST);
auto r4 = fast_float::from_chars(negative_zero, negative_zero + 2, f);
CHECK(r4.ec == std::errc());
std::cout << "FE_TONEAREST parsed negative zero as " << iHexAndDec(f) << std::endl;
CHECK(f == 0);
::memcpy(&float64_parsed, &f, sizeof(f));
std::cout << "double as uint64_t is " << float64_parsed << std::endl;
CHECK(float64_parsed == 0x8000'0000'0000'0000);
}
// C++ 17 because it is otherwise annoying to browse all files in a directory. // C++ 17 because it is otherwise annoying to browse all files in a directory.
// We also only run these tests on little endian systems. // We also only run these tests on little endian systems.
#if (FASTFLOAT_CPLUSPLUS >= 201703L) && (FASTFLOAT_IS_BIG_ENDIAN == 0) && !defined(FASTFLOAT_ODDPLATFORM) #if (FASTFLOAT_CPLUSPLUS >= 201703L) && (FASTFLOAT_IS_BIG_ENDIAN == 0) && !defined(FASTFLOAT_ODDPLATFORM)