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Integrate Grisu and sprintf digit generators

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This commit is contained in:
Victor Zverovich 2019-11-23 06:22:30 -08:00
parent 7395472dde
commit 4cf59ce734
4 changed files with 53 additions and 58 deletions
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49
include/fmt/format-inl.h
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@ -384,7 +384,8 @@ class fp {
}
// Assigns d to this and return true iff predecessor is closer than successor.
template <typename Double> bool assign(Double d) {
template <typename Double, FMT_ENABLE_IF(sizeof(Double) == sizeof(uint64_t))>
bool assign(Double d) {
// Assume double is in the format [sign][exponent][significand].
using limits = std::numeric_limits<Double>;
const int exponent_size =
@ -406,6 +407,12 @@ class fp {
return is_predecessor_closer;
}
template <typename Double, FMT_ENABLE_IF(sizeof(Double) != sizeof(uint64_t))>
bool assign(Double) {
*this = fp();
return false;
}
// Assigns d to this together with computing lower and upper boundaries,
// where a boundary is a value half way between the number and its predecessor
// (lower) or successor (upper). The upper boundary is normalized and lower
@ -1029,28 +1036,32 @@ void fallback_format(Double d, buffer<char>& buf, int& exp10) {
}
}
template <typename Float, enable_if_t<(sizeof(Float) == sizeof(uint64_t)), int>>
bool grisu_format(Float value, int precision, buffer<char>& buf,
float_spec spec, int& exp) {
// Formats value using the Grisu algorithm
// (https://www.cs.tufts.edu/~nr/cs257/archive/florian-loitsch/printf.pdf)
// if Float is a IEEE754 binary32 or binary64 and snprintf otherwise.
template <typename T>
int format_float(T value, int precision, float_spec spec, buffer<char>& buf) {
FMT_ASSERT(value >= 0, "value is negative");
static_assert(!std::is_same<T, float>(), "");
const bool fixed = spec.format == float_format::fixed;
if (value <= 0) { // <= instead of == to silence a warning.
if (precision <= 0 || !fixed) {
exp = 0;
buf.push_back('0');
} else {
exp = -precision;
buf.resize(to_unsigned(precision));
std::uninitialized_fill_n(buf.data(), precision, '0');
return 0;
}
return true;
buf.resize(to_unsigned(precision));
std::uninitialized_fill_n(buf.data(), precision, '0');
return -precision;
}
if (!spec.use_grisu) return snprintf_float(value, precision, spec, buf);
int exp = 0;
const int min_exp = -60; // alpha in Grisu.
int cached_exp10 = 0; // K in Grisu.
if (precision != -1) {
if (precision > 17) return false;
if (precision > 17) return snprintf_float(value, precision, spec, buf);
fp fp_value(value);
fp normalized = normalize(fp_value);
const auto cached_pow = get_cached_power(
@ -1058,7 +1069,7 @@ bool grisu_format(Float value, int precision, buffer<char>& buf,
normalized = normalized * cached_pow;
fixed_handler handler{buf.data(), 0, precision, -cached_exp10, fixed};
if (grisu_gen_digits(normalized, 1, exp, handler) == digits::error)
return false;
return snprintf_float(value, precision, spec, buf);
int num_digits = handler.size;
if (!fixed) {
// Remove trailing zeros.
@ -1075,7 +1086,6 @@ bool grisu_format(Float value, int precision, buffer<char>& buf,
fp_value.assign_float_with_boundaries(value, lower, upper);
else
fp_value.assign_with_boundaries(value, lower, upper);
// Find a cached power of 10 such that multiplying upper by it will bring
// the exponent in the range [min_exp, -32].
const auto cached_pow = get_cached_power( // \tilde{c}_{-k} in Grisu.
@ -1095,19 +1105,18 @@ bool grisu_format(Float value, int precision, buffer<char>& buf,
if (result == digits::error) {
exp = exp + size - cached_exp10 - 1;
fallback_format(value, buf, exp);
return true;
return exp;
}
buf.resize(to_unsigned(size));
}
exp -= cached_exp10;
return true;
return exp - cached_exp10;
}
template <typename Float>
int sprintf_format(Float value, int precision, float_spec spec,
buffer<char>& buf) {
template <typename T>
int snprintf_float(T value, int precision, float_spec spec, buffer<char>& buf) {
// Buffer capacity must be non-zero, otherwise MSVC's vsnprintf_s will fail.
FMT_ASSERT(buf.capacity() > buf.size(), "empty buffer");
static_assert(!std::is_same<T, float>(), "");
// Subtract 1 to account for the difference in precision since we use %e for
// both general and exponent format.
@ -1124,7 +1133,7 @@ int sprintf_format(Float value, int precision, float_spec spec,
*format_ptr++ = '.';
*format_ptr++ = '*';
}
if (std::is_same<Float, long double>()) *format_ptr++ = 'L';
if (std::is_same<T, long double>()) *format_ptr++ = 'L';
*format_ptr++ = spec.format != float_format::hex
? (spec.format == float_format::fixed ? 'f' : 'e')
: (spec.upper ? 'A' : 'a');

41
include/fmt/format.h
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@ -1076,6 +1076,7 @@ struct float_spec {
bool percent;
bool alt;
bool binary32;
bool use_grisu;
};
struct gen_digits_params {
@ -1208,25 +1209,15 @@ template <typename Char> class float_writer {
}
};
// Formats value using the Grisu algorithm:
// https://www.cs.tufts.edu/~nr/cs257/archive/florian-loitsch/printf.pdf
template <typename Float, FMT_ENABLE_IF(sizeof(Float) == sizeof(uint64_t))>
FMT_API bool grisu_format(Float, int, buffer<char>&, float_spec, int&);
template <typename Float, FMT_ENABLE_IF(sizeof(Float) != sizeof(uint64_t))>
inline bool grisu_format(Float, int, buffer<char>&, float_spec, int&) {
return false;
}
template <typename T>
int format_float(T value, int precision, float_spec spec, buffer<char>& buf);
template <typename Float>
int sprintf_format(Float value, int precision, float_spec spec,
buffer<char>& buf);
// Formats a floating-point number with snprintf.
template <typename T>
int snprintf_float(T value, int precision, float_spec spec, buffer<char>& buf);
template <>
inline int sprintf_format<float>(float value, int precision, float_spec spec,
buffer<char>& buf) {
// sprintf does not support float so convert to double.
return sprintf_format<double>(value, precision, spec, buf);
}
template <typename T> T promote_float(T value) { return value; }
inline double promote_float(float value) { return value; }
template <typename Handler>
FMT_CONSTEXPR void handle_int_type_spec(char spec, Handler&& handler) {
@ -1715,7 +1706,9 @@ template <typename Range> class basic_writer {
return write_padded(specs, inf_or_nan_writer<char_type>{sign, str});
}
if (specs.align == align::numeric) {
if (specs.align == align::none) {
specs.align = align::right;
} else if (specs.align == align::numeric) {
if (sign) {
auto&& it = reserve(1);
*it++ = static_cast<char_type>(data::signs[sign]);
@ -1723,28 +1716,22 @@ template <typename Range> class basic_writer {
if (specs.width != 0) --specs.width;
}
specs.align = align::right;
} else if (specs.align == align::none) {
specs.align = align::right;
}
memory_buffer buffer;
if (fspec.format == float_format::hex) {
if (sign) buffer.push_back(data::signs[sign]);
fspec.alt = specs.alt;
sprintf_format(value, specs.precision, fspec, buffer);
snprintf_float(promote_float(value), specs.precision, fspec, buffer);
write_padded(specs, str_writer<char>{buffer.data(), buffer.size()});
return;
}
int precision = specs.precision >= 0 || !specs.type ? specs.precision : 6;
if (fspec.format == float_format::exp) ++precision;
if (const_check(std::is_same<T, float>())) fspec.binary32 = true;
fspec.use_grisu = use_grisu<T>();
if (const_check(FMT_DEPRECATED_PERCENT) && fspec.percent) value *= 100;
int exp = 0;
bool use_grisu =
internal::use_grisu<T>() &&
grisu_format(static_cast<double>(value), precision, buffer, fspec, exp);
if (!use_grisu) exp = sprintf_format(value, precision, fspec, buffer);
int exp = format_float(promote_float(value), precision, fspec, buffer);
if (const_check(FMT_DEPRECATED_PERCENT) && fspec.percent) {
buffer.push_back('%');
--exp; // Adjust decimal place position.

18
src/format.cc
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@ -10,10 +10,10 @@
FMT_BEGIN_NAMESPACE
template struct FMT_API internal::basic_data<void>;
// Workaround a bug in MSVC2013 that prevents instantiation of grisu_format.
bool (*instantiate_grisu_format)(double, int, internal::buffer<char>&,
internal::float_spec,
int&) = internal::grisu_format;
// Workaround a bug in MSVC2013 that prevents instantiation of format_float.
int (*instantiate_format_float)(double, int, internal::float_spec,
internal::buffer<char>&) =
internal::format_float;
#ifndef FMT_STATIC_THOUSANDS_SEPARATOR
template FMT_API internal::locale_ref::locale_ref(const std::locale& loc);
@ -37,11 +37,11 @@ template FMT_API std::string internal::vformat<char>(
template FMT_API format_context::iterator internal::vformat_to(
internal::buffer<char>&, string_view, basic_format_args<format_context>);
template FMT_API int internal::sprintf_format(double, int, internal::float_spec,
internal::buffer<char>&);
template FMT_API int internal::sprintf_format(long double, int,
internal::float_spec,
internal::buffer<char>&);
template FMT_API int internal::format_float(double, int, internal::float_spec,
internal::buffer<char>&);
template FMT_API int internal::format_float(long double, int,
internal::float_spec,
internal::buffer<char>&);
// Explicit instantiations for wchar_t.

3
test/format-impl-test.cc
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@ -326,8 +326,7 @@ TEST(FPTest, FixedHandler) {
TEST(FPTest, GrisuFormatCompilesWithNonIEEEDouble) {
fmt::memory_buffer buf;
int exp = 0;
grisu_format(4.2f, -1, buf, fmt::internal::float_spec(), exp);
format_float(0.42, -1, fmt::internal::float_spec(), buf);
}
template <typename T> struct value_extractor {