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Optimize floating point formatting

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This commit is contained in:
Victor Zverovich 2020-10-09 10:23:10 -07:00
parent f6d75c534c
commit 3c13a88b14
2 changed files with 35 additions and 22 deletions
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5
include/fmt/format-inl.h
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@ -2173,11 +2173,8 @@ FMT_SAFEBUFFERS decimal_fp<T> to_decimal(T x) FMT_NOEXCEPT {
const carrier_uint significand_mask =
(static_cast<carrier_uint>(1) << float_info<T>::significand_bits) - 1;
carrier_uint significand = (br & significand_mask);
const carrier_uint exponent_mask =
((static_cast<carrier_uint>(1) << float_info<T>::exponent_bits) - 1)
<< float_info<T>::significand_bits;
int exponent =
static_cast<int>((br & exponent_mask) >> float_info<T>::significand_bits);
static_cast<int>((br & exponent_mask<T>()) >> float_info<T>::significand_bits);
if (exponent != 0) { // Check if normal.
exponent += float_info<T>::exponent_bias - float_info<T>::significand_bits;

52
include/fmt/format.h
View File

@ -1269,6 +1269,13 @@ template <typename T> struct decimal_fp {
template <typename T> decimal_fp<T> to_decimal(T x) FMT_NOEXCEPT;
} // namespace dragonbox
template <typename T>
constexpr typename dragonbox::float_info<T>::carrier_uint exponent_mask() {
using uint = typename dragonbox::float_info<T>::carrier_uint;
return ((uint(1) << dragonbox::float_info<T>::exponent_bits) - 1)
<< dragonbox::float_info<T>::significand_bits;
}
// A floating-point presentation format.
enum class float_format : unsigned char {
general, // General: exponent notation or fixed point based on magnitude.
@ -1791,7 +1798,7 @@ OutputIt write_float(OutputIt out, const DecimalFP& fp,
Char decimal_point) {
auto significand = fp.significand;
int significand_size = get_significand_size(fp);
const Char zero = static_cast<Char>('0');
static const Char zero = static_cast<Char>('0');
char sign = data::signs[fspecs.sign];
int size = significand_size + (fspecs.sign ? 1 : 0);
using iterator = remove_reference_t<decltype(reserve(out, 0))>;
@ -1822,16 +1829,19 @@ OutputIt write_float(OutputIt out, const DecimalFP& fp,
size += (decimal_point ? 1 : 0) + num_zeros + 2 + exp_digits;
char exp_char = fspecs.upper ? 'E' : 'e';
return write_padded<align::right>(
out, specs, to_unsigned(size), [=](iterator it) mutable {
if (sign) *it++ = static_cast<Char>(sign);
// Insert a decimal point after the first digit and add an exponent.
it = write_significand(it, significand, significand_size, 1,
decimal_point);
if (num_zeros > 0) it = std::fill_n(it, num_zeros, zero);
*it++ = static_cast<Char>(exp_char);
return write_exponent<Char>(output_exp, it);
});
auto write = [=](iterator it) {
if (sign) *it++ = static_cast<Char>(sign);
// Insert a decimal point after the first digit and add an exponent.
it = write_significand(it, significand, significand_size, 1,
decimal_point);
if (num_zeros > 0) it = std::fill_n(it, num_zeros, zero);
*it++ = static_cast<Char>(exp_char);
return write_exponent<Char>(output_exp, it);
};
auto usize = to_unsigned(size);
return specs.width > 0
? write_padded<align::right>(out, specs, usize, write)
: base_iterator(out, write(reserve(out, usize)));
}
int exp = fp.exponent + significand_size;
@ -1848,7 +1858,7 @@ OutputIt write_float(OutputIt out, const DecimalFP& fp,
if (num_zeros > 0) size += num_zeros;
}
return write_padded<align::right>(
out, specs, to_unsigned(size), [&](iterator it) mutable {
out, specs, to_unsigned(size), [&](iterator it) {
if (sign) *it++ = static_cast<Char>(sign);
it = write_significand<Char>(it, significand, significand_size);
it = std::fill_n(it, fp.exponent, zero);
@ -1861,7 +1871,7 @@ OutputIt write_float(OutputIt out, const DecimalFP& fp,
int num_zeros = fspecs.showpoint ? fspecs.precision - significand_size : 0;
size += 1 + (num_zeros > 0 ? num_zeros : 0);
return write_padded<align::right>(
out, specs, to_unsigned(size), [&](iterator it) mutable {
out, specs, to_unsigned(size), [&](iterator it) {
if (sign) *it++ = static_cast<Char>(sign);
it = write_significand(it, significand, significand_size, exp,
decimal_point);
@ -1876,7 +1886,7 @@ OutputIt write_float(OutputIt out, const DecimalFP& fp,
}
size += 2 + num_zeros;
return write_padded<align::right>(
out, specs, to_unsigned(size), [&](iterator it) mutable {
out, specs, to_unsigned(size), [&](iterator it) {
if (sign) *it++ = static_cast<Char>(sign);
*it++ = zero;
if (num_zeros == 0 && significand_size == 0 && !fspecs.showpoint)
@ -1939,17 +1949,23 @@ template <typename Char, typename OutputIt, typename T,
FMT_ENABLE_IF(is_fast_float<T>::value)>
OutputIt write(OutputIt out, T value) {
if (const_check(!is_supported_floating_point(value))) return out;
using type = conditional_t<std::is_same<T, long double>::value, double, T>;
using uint = typename dragonbox::float_info<type>::carrier_uint;
auto bits = bit_cast<uint>(value);
auto fspecs = float_specs();
if (std::signbit(value)) { // value < 0 is false for NaN so use signbit.
auto sign_bit = bits & (uint(1) << (num_bits<uint>() - 1));
if (sign_bit != 0) {
fspecs.sign = sign::minus;
value = -value;
}
auto specs = basic_format_specs<Char>();
if (!std::isfinite(value))
static const auto specs = basic_format_specs<Char>();
uint mask = exponent_mask<type>();
if ((bits & mask) == mask)
return write_nonfinite(out, std::isinf(value), specs, fspecs);
using type = conditional_t<std::is_same<T, long double>::value, double, T>;
auto dec = dragonbox::to_decimal(static_cast<type>(value));
return write_float(out, dec, specs, fspecs, static_cast<Char>('.'));
}