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Cleanup exponent handling in write_float

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This commit is contained in:
Victor Zverovich 2020-10-07 13:27:46 -07:00
parent b347b3023f
commit 7eddbfed53
2 changed files with 40 additions and 26 deletions
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64
include/fmt/format.h
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@ -1724,37 +1724,46 @@ OutputIt write_nonfinite(OutputIt out, bool isinf,
});
}
// A decimal floating-point number significand * pow(10, exp).
struct big_decimal_fp {
const char* significand;
int significand_size;
int exp;
};
template <typename OutputIt, typename Char>
OutputIt write_float(OutputIt out, const buffer<char>& significand, int exp,
float_specs specs, Char decimal_point) {
const char* digits = significand.data();
int num_digits = static_cast<int>(significand.size());
exp += num_digits;
OutputIt write_float(OutputIt out, const big_decimal_fp& fp, float_specs specs,
Char decimal_point) {
const char* digits = fp.significand;
const Char zero = static_cast<Char>('0');
int output_exp = fp.exp + fp.significand_size - 1;
auto use_exp_format = [=]() {
if (specs.format == float_format::exp) return true;
if (specs.format != float_format::general) return false;
const int exp_threshold = -4; // Prefer 0.0001 to 1e-04.
return exp - 1 < exp_threshold ||
exp - 1 >= (specs.precision > 0 ? specs.precision : 17);
// Format numbers with the exponent in [exp_lower, exp_upper) using
// the fixed notation, e.g. prefer 0.0001 to 1e-04.
const int exp_lower = -4, exp_upper = 16;
return output_exp < exp_lower ||
output_exp >= (specs.precision > 0 ? specs.precision : exp_upper);
};
if (use_exp_format()) {
// Insert a decimal point after the first digit and add an exponent.
*out++ = static_cast<Char>(*digits);
int num_zeros = specs.precision - num_digits;
if (num_digits > 1 || specs.showpoint) *out++ = decimal_point;
out = copy_str<Char>(digits + 1, digits + num_digits, out);
int num_zeros = specs.precision - fp.significand_size;
if (fp.significand_size > 1 || specs.showpoint) *out++ = decimal_point;
out = copy_str<Char>(digits + 1, digits + fp.significand_size, out);
if (num_zeros > 0 && specs.showpoint)
out = std::fill_n(out, num_zeros, zero);
*out++ = static_cast<Char>(specs.upper ? 'E' : 'e');
return write_exponent<Char>(exp - 1, out);
return write_exponent<Char>(output_exp, out);
}
if (num_digits <= exp) {
int exp = fp.exp + fp.significand_size;
if (fp.significand_size <= exp) {
// 1234e7 -> 12340000000[.0+]
out = copy_str<Char>(digits, digits + num_digits, out);
out = std::fill_n(out, exp - num_digits, zero);
out = copy_str<Char>(digits, digits + fp.significand_size, out);
out = std::fill_n(out, exp - fp.significand_size, zero);
if (specs.showpoint) {
*out++ = decimal_point;
int num_zeros = specs.precision - exp;
@ -1772,24 +1781,26 @@ OutputIt write_float(OutputIt out, const buffer<char>& significand, int exp,
// 1234e-2 -> 12.34[0+]
out = copy_str<Char>(digits, digits + exp, out);
if (!specs.showpoint) {
if (num_digits != exp) *out++ = decimal_point;
return copy_str<Char>(digits + exp, digits + num_digits, out);
if (fp.significand_size != exp) *out++ = decimal_point;
return copy_str<Char>(digits + exp, digits + fp.significand_size, out);
}
*out++ = decimal_point;
out = copy_str<Char>(digits + exp, digits + num_digits, out);
out = copy_str<Char>(digits + exp, digits + fp.significand_size, out);
// Add trailing zeros.
if (specs.precision > num_digits)
out = std::fill_n(out, specs.precision - num_digits, zero);
if (specs.precision > fp.significand_size)
out = std::fill_n(out, specs.precision - fp.significand_size, zero);
} else {
// 1234e-6 -> 0.001234
*out++ = zero;
int num_zeros = -exp;
if (num_digits == 0 && specs.precision >= 0 && specs.precision < num_zeros)
if (fp.significand_size == 0 && specs.precision >= 0 &&
specs.precision < num_zeros) {
num_zeros = specs.precision;
if (num_zeros != 0 || num_digits != 0 || specs.showpoint) {
}
if (num_zeros != 0 || fp.significand_size != 0 || specs.showpoint) {
*out++ = decimal_point;
out = std::fill_n(out, num_zeros, zero);
out = copy_str<Char>(digits, digits + num_digits, out);
out = copy_str<Char>(digits, digits + fp.significand_size, out);
}
}
return out;
@ -1800,14 +1811,15 @@ template <typename OutputIt, typename Char>
OutputIt write_float(OutputIt out, const buffer<char>& significand, int exp,
const basic_format_specs<Char>& specs, float_specs fspecs,
Char decimal_point) {
auto fp = big_decimal_fp{significand.data(),
static_cast<int>(significand.size()), exp};
auto size =
write_float(counting_iterator(), significand, exp, fspecs, decimal_point)
.count();
write_float(counting_iterator(), fp, fspecs, decimal_point).count();
size += fspecs.sign ? 1 : 0;
using iterator = remove_reference_t<decltype(reserve(out, 0))>;
return write_padded<align::right>(out, specs, size, [&](iterator it) {
if (fspecs.sign) *it++ = static_cast<Char>(data::signs[fspecs.sign]);
return write_float(it, significand, exp, fspecs, decimal_point);
return write_float(it, fp, fspecs, decimal_point);
});
}

2
test/format-test.cc
View File

@ -1294,6 +1294,8 @@ TEST(FormatterTest, PrecisionRounding) {
TEST(FormatterTest, PrettifyFloat) {
EXPECT_EQ("0.0001", fmt::format("{}", 1e-4));
EXPECT_EQ("1e-05", fmt::format("{}", 1e-5));
EXPECT_EQ("1000000000000000", fmt::format("{}", 1e15));
EXPECT_EQ("1e+16", fmt::format("{}", 1e16));
EXPECT_EQ("9.999e-05", fmt::format("{}", 9.999e-5));
EXPECT_EQ("10000000000", fmt::format("{}", 1e10));
EXPECT_EQ("100000000000", fmt::format("{}", 1e11));