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Use exponent digit count

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This commit is contained in:
Krystian Stasiowski
2020-02-22 19:00:54 -05:00
parent 74e2395a2f
commit 50a91d6088
1 changed files with 34 additions and 30 deletions
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64
include/boost/static_string/static_string.hpp
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@ -457,7 +457,8 @@ to_static_wstring_int_impl(Integer value) noexcept
BOOST_STATIC_STRING_CPP11_CONSTEXPR BOOST_STATIC_STRING_CPP11_CONSTEXPR
inline inline
std::size_t count_digits(std::size_t value) std::size_t
count_digits(std::size_t value)
{ {
return value < 10 ? 1 : count_digits(value / 10) + 1; return value < 10 ? 1 : count_digits(value / 10) + 1;
} }
@ -469,26 +470,17 @@ to_static_string_float_impl(double value) noexcept
{ {
// extra one needed for null terminator // extra one needed for null terminator
char buffer[N + 1]; char buffer[N + 1];
// since our buffer has a fixed size, if the number of characters
// that would be written exceeds the size of the buffer,
// we need touse scientific notation instead.
// the number is converted into the format
// [-]d.ddde(+/-)dd; the exponent will contain at least
// 2 digits, the integral part will be 1 digit, the fractional
// part will be the length of the specified precision, and 3
// characters will be needed for e, the sign of the exponent
// and the potential sign of the integral part, total of 6 chars.
// we will reserve 7 characters just in case the size of the exponent
// is 3 characters.
// snprintf returns the number of characters
// that would have been written
if (std::snprintf(buffer, N + 1, "%f", value) > N) if (std::snprintf(buffer, N + 1, "%f", value) > N)
{ {
const auto period = const auto period =
std::char_traits<char>::find(buffer, N, '.'); std::char_traits<char>::find(buffer, N, '.');
const int reserved_count =
(std::max)(std::size_t(2), count_digits(
std::numeric_limits<double>::max_exponent10)) + 4;
const int precision = N > reserved_count ? N - reserved_count : 0;
// we want at least 2 decimal places // we want at least 2 decimal places
if (!period || std::size_t(period - buffer) > N - 3) if (!period || std::size_t(period - buffer) > N - 3)
std::snprintf(buffer, N + 1, "%.*e", int(N > 7 ? N - 7 : 0), value); std::snprintf(buffer, N + 1, "%.*e", precision, value);
} }
// this will not throw // this will not throw
return static_string<N>(buffer); return static_string<N>(buffer);
@ -507,9 +499,13 @@ to_static_string_float_impl(long double value) noexcept
{ {
const auto period = const auto period =
std::char_traits<char>::find(buffer, N, '.'); std::char_traits<char>::find(buffer, N, '.');
const int reserved_count =
(std::max)(std::size_t(2), count_digits(
std::numeric_limits<long double>::max_exponent10)) + 4;
const int precision = N > reserved_count ? N - reserved_count : 0;
// we want at least 2 decimal places // we want at least 2 decimal places
if (!period || std::size_t(period - buffer) > N - 3) if (!period || std::size_t(period - buffer) > N - 3)
std::snprintf(buffer, N + 1, "%.*Le", int(N > 7 ? N - 7 : 0), value); std::snprintf(buffer, N + 1, "%.*Le", precision, value);
} }
// this will not throw // this will not throw
return static_string<N>(buffer); return static_string<N>(buffer);
@ -528,9 +524,13 @@ to_static_wstring_float_impl(double value) noexcept
{ {
const auto period = const auto period =
std::char_traits<wchar_t>::find(buffer, N, '.'); std::char_traits<wchar_t>::find(buffer, N, '.');
const int reserved_count =
(std::max)(std::size_t(2), count_digits(
std::numeric_limits<double>::max_exponent10)) + 4;
const int precision = N > reserved_count ? N - reserved_count : 0;
// we want at least 2 decimal places // we want at least 2 decimal places
if (!period || std::size_t(period - buffer) > N - 3) if (!period || std::size_t(period - buffer) > N - 3)
std::swprintf(buffer, N + 1, L"%.*e", int(N > 7 ? N - 7 : 0), value); std::swprintf(buffer, N + 1, L"%.*e", precision, value);
} }
// this will not throw // this will not throw
return static_wstring<N>(buffer); return static_wstring<N>(buffer);
@ -549,9 +549,13 @@ to_static_wstring_float_impl(long double value) noexcept
{ {
const auto period = const auto period =
std::char_traits<wchar_t>::find(buffer, N, '.'); std::char_traits<wchar_t>::find(buffer, N, '.');
const int reserved_count =
(std::max)(std::size_t(2), count_digits(
std::numeric_limits<long double>::max_exponent10)) + 4;
const int precision = N > reserved_count ? N - reserved_count : 0;
// we want at least 2 decimal places // we want at least 2 decimal places
if (!period || std::size_t(period - buffer) > N - 3) if (!period || std::size_t(period - buffer) > N - 3)
std::swprintf(buffer, N + 1, L"%.*Le", int(N > 7 ? N - 7 : 0), value); std::swprintf(buffer, N + 1, L"%.*Le", precision, value);
} }
// this will not throw // this will not throw
return static_wstring<N>(buffer); return static_wstring<N>(buffer);
@ -4640,30 +4644,30 @@ to_static_string(unsigned long long value) noexcept
} }
/// Converts `value` to a `static_string` /// Converts `value` to a `static_string`
static_string<std::numeric_limits<float>::max_digits10 + 1> static_string<std::numeric_limits<float>::max_digits10 + 3>
inline inline
to_static_string(float value) noexcept to_static_string(float value) noexcept
{ {
return detail::to_static_string_float_impl< return detail::to_static_string_float_impl<
std::numeric_limits<float>::max_digits10 + 1>(value); std::numeric_limits<float>::max_digits10 + 3>(value);
} }
/// Converts `value` to a `static_string` /// Converts `value` to a `static_string`
static_string<std::numeric_limits<double>::max_digits10 + 1> static_string<std::numeric_limits<double>::max_digits10 + 3>
inline inline
to_static_string(double value) noexcept to_static_string(double value) noexcept
{ {
return detail::to_static_string_float_impl< return detail::to_static_string_float_impl<
std::numeric_limits<double>::max_digits10 + 1>(value); std::numeric_limits<double>::max_digits10 + 3>(value);
} }
/// Converts `value` to a `static_string` /// Converts `value` to a `static_string`
static_string<std::numeric_limits<long double>::max_digits10 + 1> static_string<std::numeric_limits<long double>::max_digits10 + 3>
inline inline
to_static_string(long double value) noexcept to_static_string(long double value) noexcept
{ {
return detail::to_static_string_float_impl< return detail::to_static_string_float_impl<
std::numeric_limits<long double>::max_digits10 + 1>(value); std::numeric_limits<long double>::max_digits10 + 3>(value);
} }
/// Converts `value` to a `static_wstring` /// Converts `value` to a `static_wstring`
@ -4721,30 +4725,30 @@ to_static_wstring(unsigned long long value) noexcept
} }
/// Converts `value` to a `static_wstring` /// Converts `value` to a `static_wstring`
static_wstring<std::numeric_limits<float>::max_digits10 + 1> static_wstring<std::numeric_limits<float>::max_digits10 + 3>
inline inline
to_static_wstring(float value) noexcept to_static_wstring(float value) noexcept
{ {
return detail::to_static_wstring_float_impl< return detail::to_static_wstring_float_impl<
std::numeric_limits<float>::max_digits10 + 1>(value); std::numeric_limits<float>::max_digits10 + 3>(value);
} }
/// Converts `value` to a `static_wstring` /// Converts `value` to a `static_wstring`
static_wstring<std::numeric_limits<double>::max_digits10 + 1> static_wstring<std::numeric_limits<double>::max_digits10 + 3>
inline inline
to_static_wstring(double value) noexcept to_static_wstring(double value) noexcept
{ {
return detail::to_static_wstring_float_impl< return detail::to_static_wstring_float_impl<
std::numeric_limits<double>::max_digits10 + 1>(value); std::numeric_limits<double>::max_digits10 + 3>(value);
} }
/// Converts `value` to a `static_wstring` /// Converts `value` to a `static_wstring`
static_wstring<std::numeric_limits<long double>::max_digits10 + 1> static_wstring<std::numeric_limits<long double>::max_digits10 + 3>
inline inline
to_static_wstring(long double value) noexcept to_static_wstring(long double value) noexcept
{ {
return detail::to_static_wstring_float_impl< return detail::to_static_wstring_float_impl<
std::numeric_limits<long double>::max_digits10 + 1>(value); std::numeric_limits<long double>::max_digits10 + 3>(value);
} }
//------------------------------------------------------------------------------ //------------------------------------------------------------------------------