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在头文件<math.h>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 <tgmath.h> | ||
#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。
from, to | - | 浮点值 |
---|
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。
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
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
。
#include <math.h>#include <stdio.h>#include <float.h>#include <fenv.h> 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)
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<tgmath.h>(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<tgmath.h>(p:335-337)
F.9.8.3 nextafter函数(p:466)
F.9.8.4 nexttoward函数(p:466)