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Workaround broken std::numeric_limits

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This commit is contained in:
Victor Zverovich 2022-03-20 07:51:46 -07:00
parent 8271e43e5e
commit db745986f2
2 changed files with 27 additions and 32 deletions
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45
include/fmt/format-inl.h
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@ -212,42 +212,36 @@ template <typename F> struct basic_fp {
constexpr basic_fp() : f(0), e(0) {}
constexpr basic_fp(uint64_t f_val, int e_val) : f(f_val), e(e_val) {}
// Constructs fp from an IEEE754 floating-point number. It is a template to
// prevent compile errors on systems where n is not IEEE754.
// Constructs fp from an IEEE754 floating-point number.
template <typename Float> FMT_CONSTEXPR basic_fp(Float n) { assign(n); }
template <typename Float>
using is_supported =
bool_constant<(std::numeric_limits<Float>::is_iec559 &&
std::numeric_limits<Float>::digits <= 113) ||
is_float128<Float>::value>;
// Assigns d to this and return true iff predecessor is closer than successor.
template <typename Float, FMT_ENABLE_IF(is_supported<Float>::value)>
FMT_CONSTEXPR bool assign(Float n) {
// Assume float is in the format [sign][exponent][significand].
// Assigns n to this and return true iff predecessor is closer than successor.
template <typename Float> FMT_CONSTEXPR bool assign(Float n) {
static_assert((std::numeric_limits<Float>::is_iec559 &&
std::numeric_limits<Float>::digits <= 113) ||
is_float128<Float>::value,
"unsupported FP");
// Assume Float is in the format [sign][exponent][significand].
using carrier_uint = typename dragonbox::float_info<Float>::carrier_uint;
const carrier_uint implicit_bit = carrier_uint(1)
<< detail::num_significand_bits<Float>();
const carrier_uint significand_mask = implicit_bit - 1;
constexpr auto num_float_significand_bits =
detail::num_significand_bits<Float>();
constexpr auto implicit_bit = carrier_uint(1) << num_float_significand_bits;
constexpr auto significand_mask = implicit_bit - 1;
auto u = bit_cast<carrier_uint>(n);
f = static_cast<F>(u & significand_mask);
int biased_e = static_cast<int>((u & exponent_mask<Float>()) >>
detail::num_significand_bits<Float>());
auto biased_e = static_cast<int>((u & exponent_mask<Float>()) >>
num_float_significand_bits);
// The predecessor is closer if n is a normalized power of 2 (f == 0) other
// than the smallest normalized number (biased_e > 1).
bool is_predecessor_closer = f == 0 && biased_e > 1;
auto is_predecessor_closer = f == 0 && biased_e > 1;
if (biased_e != 0)
f += static_cast<uint64_t>(implicit_bit);
f += static_cast<F>(implicit_bit);
else
biased_e = 1; // Subnormals use biased exponent 1 (min exponent).
const int exponent_bias = std::numeric_limits<Float>::max_exponent - 1;
e = biased_e - exponent_bias - std::numeric_limits<Float>::digits + 1;
e = biased_e - exponent_bias<Float>() - num_float_significand_bits;
if (!has_implicit_bit<Float>()) ++e;
return is_predecessor_closer;
}
template <typename Float, FMT_ENABLE_IF(!is_supported<Float>::value)>
bool assign(Float) = delete;
};
using fp = basic_fp<unsigned long long>;
@ -1917,8 +1911,7 @@ template <typename T> decimal_fp<T> to_decimal(T x) noexcept {
static_cast<int>((br & exponent_mask<T>()) >> num_significand_bits<T>());
if (exponent != 0) { // Check if normal.
const int exponent_bias = std::numeric_limits<T>::max_exponent - 1;
exponent -= exponent_bias + num_significand_bits<T>();
exponent -= exponent_bias<T>() + num_significand_bits<T>();
// Shorter interval case; proceed like Schubfach.
// In fact, when exponent == 1 and significand == 0, the interval is

14
include/fmt/format.h
View File

@ -1308,6 +1308,11 @@ constexpr auto exponent_mask() ->
return ((uint(1) << dragonbox::float_info<Float>::exponent_bits) - 1)
<< num_significand_bits<Float>();
}
template <typename Float> constexpr auto exponent_bias() -> int {
// std::numeric_limits may not support __float128.
return is_float128<Float>() ? 16383
: std::numeric_limits<Float>::max_exponent - 1;
}
// Writes the exponent exp in the form "[+-]d{2,3}" to buffer.
template <typename Char, typename It>
@ -2370,13 +2375,8 @@ template <typename Char, typename OutputIt, typename T,
FMT_CONSTEXPR20 auto write(OutputIt out, T value) -> OutputIt {
if (is_constant_evaluated())
return write(out, value, basic_format_specs<Char>());
if (const_check(!is_supported_floating_point(value))) return out;
using floaty = conditional_t<std::is_same<T, long double>::value, double, T>;
using uint = typename dragonbox::float_info<floaty>::carrier_uint;
auto bits = bit_cast<uint>(value);
auto fspecs = float_specs();
if (detail::signbit(value)) {
fspecs.sign = sign::minus;
@ -2384,8 +2384,10 @@ FMT_CONSTEXPR20 auto write(OutputIt out, T value) -> OutputIt {
}
constexpr auto specs = basic_format_specs<Char>();
using floaty = conditional_t<std::is_same<T, long double>::value, double, T>;
using uint = typename dragonbox::float_info<floaty>::carrier_uint;
uint mask = exponent_mask<floaty>();
if ((bits & mask) == mask)
if ((bit_cast<uint>(value) & mask) == mask)
return write_nonfinite(out, std::isnan(value), specs, fspecs);
auto dec = dragonbox::to_decimal(static_cast<floaty>(value));