c语言 l l next,nexttowardl

在头文件中定义float nextafterf( float from, float to );(1)(since C99)

double nextafter( double from, double to );(2)(since C99)

long double nextafterl( long double from, long double to );(3)(since C99)

float nexttowardf( float from, long double to );(4)(since C99)

double nexttoward( double from, long double to );(5)(since C99)

long double nexttowardl( long double from, long double to );(6)(since C99)

Defined in header

#define nextafter(from, to)(7)(since C99)

#define nexttoward(from, to)(8)(since C99)

1-3)首先，将两个参数都转换为函数的类型，然后返回下一个可表示值from的方向to。如果from等于to，to则返回。

4-6)首先，将第一个参数转换为函数的类型，然后返回下一个可表示值from的方向to。如果from等于to，to则返回，转换long double为函数的返回类型，但不会丢失范围或精度。

7)类型 - 通用宏：如果任何参数具有类型long double，nextafterl则被调用。否则，如果任何参数具有整数类型或具有类型double，nextafter则被调用。否则，nextafterf被调用。

8)类型 - 通用宏：如果参数from具有类型long double，nexttowardl则被调用。否则，如果from有整数类型或类型double，nexttoward则调用。否则，nexttowardf被调用。

参数

from, to-浮点值

返回值

如果没有错误发生，下一个可表示值from的方向to。返回。如果from等于to，则to返回，转换为函数的类型。

如果范围误差由于发生溢出，±HUGE_VAL，±HUGE_VALF，或±HUGE_VALL被返回(与相同的符号from)。

如果由于下溢而发生范围错误，则返回正确的结果。

错误处理

按照math_errhandling中的指定报告错误。

如果实现支持IEEE浮点运算(IEC 60559)，

如果from是有限的，但预期的结果是无穷大，提高FE_INEXACT和FE_OVERFLOW

如果from不相等to，结果是低于正常或零，则引发FE_INEXACT和FE_UNDERFLOW

在任何情况下，返回值都与当前舍入模式无关

如果是from或者to是NaN，则返回NaN

笔记

POSIX指定溢出和下溢条件是范围错误(可能会设置错误)。

IEC 60559建议from每当返回from==to。这些函数会返回to，这会使零之间的行为保持一致：nextafter(-0.0, +0.0)返回+0.0并nextafter(+0.0, -0.0)返回–0.0。

例

#include #include #include #include

int main(void){

float from1 = 0, to1 = nextafterf(from1, 1); printf("The next representable float after %.2f is %.20g (%a)\n", from1, to1, to1);

float from2 = 1, to2 = nextafterf(from2, 2); printf("The next representable float after %.2f is %.20f (%a)\n", from2, to2, to2);

double from3 = nextafter(0.1, 0), to3 = 0.1; printf("The number 0.1 lies between two valid doubles:\n" " %.56f (%a)\nand %.55f (%a)\n", from3, from3, to3, to3);

// difference between nextafter and nexttoward:

long double dir = nextafterl(from1, 1); // first subnormal long double

float x = nextafterf(from1, dir); // first converts dir to float, giving 0 printf("Using nextafter, next float after %.2f (%a) is %.20g (%a)\n",

from1, from1, x, x);

x = nexttowardf(from1, dir); printf("Using nexttoward, next float after %.2f (%a) is %.20g (%a)\n",

from1, from1, x, x);

// special values {

#pragma STDC FENV_ACCESS ON feclearexcept(FE_ALL_EXCEPT);

double from4 = DBL_MAX, to4 = nextafter(from4, INFINITY); printf("The next representable double after %.2g (%a) is %.23f (%a)\n",

from4, from4, to4, to4); if(fetestexcept(FE_OVERFLOW)) puts(" raised FE_OVERFLOW"); if(fetestexcept(FE_INEXACT)) puts(" raised FE_INEXACT"); } // end FENV_ACCESS block

float from5 = 0.0, to5 = nextafter(from5, -0.0); printf("nextafter(+0.0, -0.0) gives %.2g (%a)\n", to5, to5);}

输出：

The next representable float after 0.00 is 1.4012984643248170709e-45 (0x1p-149)The next representable float after 1.00 is 1.00000011920928955078 (0x1.000002p+0)The number 0.1 lies between two valid doubles: 0.09999999999999999167332731531132594682276248931884765625 (0x1.9999999999999p-4)and 0.1000000000000000055511151231257827021181583404541015625 (0x1.999999999999ap-4)Using nextafter, next float after 0.00 (0x0p+0) is 0 (0x0p+0)Using nexttoward, next float after 0.00 (0x0p+0) is 1.4012984643248170709e-45 (0x1p-149)The next representable double after 1.8e+308 (0x1.fffffffffffffp+1023) is inf (inf)

raised FE_OVERFLOW

raised FE_INEXACTnextafter(+0.0, -0.0) gives -0 (-0x0p+0)

参考

C11标准(ISO / IEC 9899：2011)：7.12.11.3 nextafter函数(p：256)

7.12.11.4 nexttoward函数(p：257)

7.25类型通用数学(p：373-375)

F.10.8.3 nextafter函数(p：529)

F.10.8.4 nexttoward函数(p：529)

C99标准(ISO / IEC 9899：1999)：7.12.11.3 nextafter函数(p：237)

7.12.11.4 nexttoward函数(p：238)

7.22类型通用数学(p：335-337)

F.9.8.3 nextafter函数(p：466)