std::numeric_limits::round_style - cppreference.com (original) (raw)
The value of std::numeric_limits<T>::round_style identifies the rounding style used by the floating-point type T whenever a value that is not one of the exactly repesentable values of T is stored in an object of that type.
[edit] Standard specializations
| T | value of std::numeric_limits<T>::round_style |
|---|---|
| /* non-specialized */ | std::round_toward_zero |
| bool | std::round_toward_zero |
| char | std::round_toward_zero |
| signed char | std::round_toward_zero |
| unsigned char | std::round_toward_zero |
| wchar_t | std::round_toward_zero |
| char8_t (since C++20) | std::round_toward_zero |
| char16_t (since C++11) | std::round_toward_zero |
| char32_t (since C++11) | std::round_toward_zero |
| short | std::round_toward_zero |
| unsigned short | std::round_toward_zero |
| int | std::round_toward_zero |
| unsigned int | std::round_toward_zero |
| long | std::round_toward_zero |
| unsigned long | std::round_toward_zero |
| long long (since C++11) | std::round_toward_zero |
| unsigned long long (since C++11) | std::round_toward_zero |
| float | usually std::round_to_nearest |
| double | usually std::round_to_nearest |
| long double | usually std::round_to_nearest |
[edit] Notes
These values are constants, and do not reflect the changes to the rounding made by std::fesetround. The changed values may be obtained from FLT_ROUNDS or std::fegetround.
[edit] Example
The decimal value 0.1 cannot be represented by a binary floating-point type. When stored in an IEEE-754 double, it falls between 0x1.9999999999999*2-4
and 0x1.999999999999a*2-4
. Rounding to nearest representable value results in 0x1.999999999999a*2-4
.
Similarly, the decimal value 0.3, which is between 0x1.3333333333333*2-2
and 0x1.3333333333334*2-2
is rounded to nearest and is stored as 0x1.3333333333333*2-2
.
Output:
The decimal 0.1 is stored in a double as 0x1.999999999999ap-4 The decimal 0.3 is stored in a double as 0x1.3333333333333p-2 Rounding toward nearest representable value