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Simplify Dragonbox integration

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This commit is contained in:
Victor Zverovich 2020-09-22 16:20:40 -07:00
parent c1654ce487
commit aa2ddf9b86
1 changed files with 9 additions and 64 deletions
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73
include/fmt/format-inl.h
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@ -2644,9 +2644,6 @@ void fallback_format(Double d, int num_digits, bool binary32, buffer<char>& buf,
buf[num_digits - 1] = static_cast<char>('0' + digit);
}
// Formats value using the Grisu algorithm
// (https://www.cs.tufts.edu/~nr/cs257/archive/florian-loitsch/printf.pdf)
// if T is an IEEE754 binary32 or binary64 and snprintf otherwise.
template <typename T>
int format_float(T value, int precision, float_specs specs, buffer<char>& buf) {
static_assert(!std::is_same<T, float>::value, "");
@ -2665,72 +2662,20 @@ int format_float(T value, int precision, float_specs specs, buffer<char>& buf) {
if (!specs.use_grisu) return snprintf_float(value, precision, specs, buf);
// Use Dragonbox for shortest
if (precision < 0) {
int length;
uint32_t dec_significand;
int i = 0;
int exponent;
// Use Dragonbox for the shortest format.
if (specs.binary32) {
detail::dragonbox::decimal_fp<float> dec =
detail::dragonbox::to_decimal(float(value));
length = detail::count_digits(dec.significand);
exponent = dec.exponent;
buf.try_resize(to_unsigned(length));
dec_significand = dec.significand;
} else {
detail::dragonbox::decimal_fp<double> dec =
detail::dragonbox::to_decimal(double(value));
length = detail::count_digits(dec.significand);
exponent = dec.exponent;
buf.try_resize(to_unsigned(length));
if (dec.significand >= 100000000) {
dec_significand = uint32_t(dec.significand / 100000000);
uint32_t r = uint32_t(dec.significand) - 100000000 * dec_significand;
uint32_t r1 = r / 10000;
uint32_t r2 = r % 10000;
uint32_t a = r1 / 100;
uint32_t b = r1 % 100;
uint32_t c = r2 / 100;
uint32_t d = r2 % 100;
copy2(buf.data() + length - 8, data::digits[a]);
copy2(buf.data() + length - 6, data::digits[b]);
copy2(buf.data() + length - 4, data::digits[c]);
copy2(buf.data() + length - 2, data::digits[d]);
i += 8;
} else {
dec_significand = uint32_t(dec.significand);
}
auto dec = dragonbox::to_decimal(static_cast<float>(value));
write<char>(buffer_appender<char>(buf), dec.significand);
return dec.exponent;
}
while (dec_significand >= 10000) {
uint32_t r = dec_significand % 10000;
dec_significand /= 10000;
copy2(buf.data() + length - i - 4, data::digits[r / 100]);
copy2(buf.data() + length - i - 2, data::digits[r % 100]);
i += 4;
}
if (dec_significand >= 100) {
uint32_t r = dec_significand % 100;
dec_significand /= 100;
copy2(buf.data() + length - i - 2, data::digits[r]);
i += 2;
}
if (dec_significand >= 10) {
copy2(buf.data() + length - i - 2, data::digits[dec_significand]);
} else {
*buf.data() = char('0' + dec_significand);
}
return exponent;
auto dec = dragonbox::to_decimal(static_cast<double>(value));
write<char>(buffer_appender<char>(buf), dec.significand);
return dec.exponent;
}
// Use Grisu + Dragon4 for fixed precision
// Use Grisu + Dragon4 for the given precision:
// https://www.cs.tufts.edu/~nr/cs257/archive/florian-loitsch/printf.pdf.
int exp = 0;
const int min_exp = -60; // alpha in Grisu.
int cached_exp10 = 0; // K in Grisu.