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std::numeric_limits::tinyness_before

提供: cppreference.com

 
 
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static const bool tinyness_before
(C + + 11時まで)
static constexpr bool tinyness_before
(C + + 11以来)
std::numeric_limits<T>::has_denorm_lossの値は、四捨五入する前のアンダーフローの浮動小数点表現のtrueすべての浮動小数点型のTそのテスト結果です.
Original:
The value of std::numeric_limits<T>::has_denorm_loss is true for all floating-point types T that test results of floating-point expressions for underflow before rounding.
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目次

[編集] 標準の専門分野

T
std::numeric_limits<T>::tinyness_beforeの値
Original:
value of std::numeric_limits<T>::tinyness_before
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/* non-specialized */ false
bool false
char false
signed char false
unsigned char false
wchar_t false
char16_t false
char32_t false
short false
unsigned short false
int false
unsigned int false
long false
unsigned long false
long long false
unsigned long long false
float
実装定義である
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implementation-defined
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double
実装定義である
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implementation-defined
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long double
実装定義である
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implementation-defined
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[編集] ノート

標準準拠IEEE 754浮動小数点の実装では、3つの事前定義された瞬間に、浮動小数点アンダーフローを検出することがあります:
Original:
Standard-compliant IEEE 754 floating-point implementations may detect the floating-point underflow at three predefined moments:
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1)
std::numeric_limits<T>::min()より絶対値が小さい方の結果の計算の後に、そのような実装は丸め(たとえばのUltraSparc)前tinynessを検出します
Original:
after computation of a result with absolute value smaller than std::numeric_limits<T>::min(), such implementation detects tinyness before rounding (e.g. UltraSparc)
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2)
結果は、小型である場合std::numeric_limits<T>::digitsビットに結果の丸めた後、このような実装では、(例えばSuperSPARCの)丸めた後tinynessを検出します
Original:
after rounding of the result to std::numeric_limits<T>::digits bits, if the result is tiny, such implementation detects tinyness after rounding (e.g. SuperSparc)
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3)
非正規形に丸みを帯びた小さな結果の変換は精度の損失をもたらした場合には、そのような実装では、非正規化数の損失を検出.
Original:
if the conversion of the rounded tiny result to subnormal form resulted in the loss of precision, such implementation detects denorm loss.
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[編集]

1.0を超えるナンバーワンマシンイプシロンで最大の非正規数の乗算は丸め前に小さな値0x0.fffffffffffff8p-1022を与えますが、正常値1P-1022丸めた後.
Original:
Multiplication of the largest subnormal number by the number one machine epsilon greater than 1.0 gives the tiny value 0x0.fffffffffffff8p-1022 before rounding, but normal value 1p-1022 after rounding.
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#include <iostream>
#include <limits>
#include <cmath>
#include <cfenv>
int main()
{
    double denorm_max = std::nextafter(std::numeric_limits<double>::min(), 0);
    double multiplier = 1 + std::numeric_limits<double>::epsilon();
 
    std::feclearexcept(FE_ALL_EXCEPT);
 
    double result = denorm_max*multiplier; // Underflow only if tinyness_before
 
    if(std::fetestexcept(FE_UNDERFLOW))
        std::cout << "Underflow detected\n";
    else if (std::fetestexcept(FE_INEXACT))
        std::cout << "Inexact result detected\n";
 
    std::cout << std::hexfloat << denorm_max << " x " << multiplier  <<  " = "
              << result << '\n';
}

Output:

Inexact result detected
0x0.fffffffffffffp-1022 x 0x1.0000000000001p+0 = 0x1p-1022

[編集] も参照してください

identifies the floating-point types that detect loss of precision as denormalization loss rather than inexact result
(公共の静的メンバ定数) [edit]
[静的]
浮動小数点型で使用される非正規のスタイルを識別します
Original:
identifies the denormalization style used by the floating-point type
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(公共の静的メンバ定数) [edit]