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[libcxx] [test] Clarify the condition for long double hex formatting #135334

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Apr 25, 2025
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[libcxx] [test] Clarify the condition for long double hex formatting #135334

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298c2c6
[libcxx] [test] Clarify the condition for long double hex formatting
mstorsjo Mar 12, 2025
c8bf9d0
Add a test define TEST_LONG_DOUBLE_IS_80_BIT in test_macros.h
mstorsjo Apr 24, 2025
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24 changes: 19 additions & 5 deletions ...egories/category.numeric/locale.nm.put/facet.num.put.members/put_long_double.hex.pass.cpp
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Expand Up @@ -1846,11 +1846,25 @@ void test1() {
void test2() {
std::locale lc = std::locale::classic();
std::locale lg(lc, new my_numpunct);
#if (defined(__APPLE__) || defined(TEST_HAS_GLIBC) || defined(__MINGW32__)) && defined(__x86_64__)
// This test is failing on FreeBSD, possibly due to different representations
// of the floating point numbers.
// This test is failing in MSVC environments, where long double is equal to regular
// double, and instead of "0x9.32c05a44p+27", this prints "0x1.26580b4880000p+30".
#if (defined(__APPLE__) || defined(TEST_HAS_GLIBC) || defined(__MINGW32__)) && defined(TEST_LONG_DOUBLE_IS_80_BIT)
// This test assumes that long doubles are x87 80 bit long doubles, and
// assumes one specific way of formatting the long doubles. (There are
// multiple valid ways of hex formatting the same float.)
//
// FreeBSD does use x87 80 bit long doubles, but normalizes the hex floats
// differently.
//
// This test assumes the form used by Glibc, Darwin and others, where the
// 64 mantissa bits are grouped by nibble as they are stored in the long
// double representation (nibble aligned at the end of the least significant
// bits). This makes 1.0L to be formatted as "0x8p-3" (where the leading
// bit of the mantissa is the higest bit in the 0x8 nibble), and makes
// __LDBL_MAX__ be formatted as "0xf.fffffffffffffffp+16380".
//
// FreeBSD normalizes/aligns the leading bit of the mantissa as a separate
// nibble, so that 1.0L is formatted as "0x1p+0" and __LDBL_MAX__ as
// "0x1.fffffffffffffffep+16383" (note the lowest bit of the last nibble
// being zero as the nibbles don't align to the actual floats).
const my_facet f(1);
char str[200];
{
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4 changes: 4 additions & 0 deletions libcxx/test/support/test_macros.h
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Expand Up @@ -544,4 +544,8 @@ inline Tp const& DoNotOptimize(Tp const& value) {
# define TEST_LONG_DOUBLE_IS_DOUBLE
#endif

#if defined(__LDBL_MANT_DIG__) && __LDBL_MANT_DIG__ == 64
# define TEST_LONG_DOUBLE_IS_80_BIT
#endif

#endif // SUPPORT_TEST_MACROS_HPP
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