nextafter(), nextafterf()

Compute the next representable double-precision floating-point number

Synopsis:

#include <math.h>

double nextafter ( double x,
                   double y);

float nextafterf ( float x,
                   float y );

Library:

libm

Description:

The nextafter() and nextafterf() functions compute the next representable double-precision floating-point value following x in the direction of y.

Returns:

The next machine floating-point number of x in the direction towards y.

Examples:

#include <stdio.h>
#include <errno.h>
#include <inttypes.h>
#include <math.h>
#include <fpstatus.h>

void dump_to_hex(double d) {
        printf("0x%08x %08x \n",
           (uint32_t)(*((uint64_t*)&d) >> 32),
           (uint32_t)(*((uint64_t*)&d)));
}

int main(int argc, char** argv) 
{
    double a, b, c;

    a = 0 ;
    b = nextafter(a, -1);
    c = nextafter(a, 1);
    printf("Next possible value before %f is %f \n", a, b);
    printf("-->"); dump_to_hex(a);
    printf("-->"); dump_to_hex(b);
    printf("Next possible value after %f is %f \n", a, c);
    printf("-->"); dump_to_hex(a);
    printf("-->"); dump_to_hex(c);

    return(0);
}

produces the output:

Next possible value before 0.000000 is 0.000000
-->0x00000000 00000000
-->0x80000000 00000001
Next possible value after 0.000000 is 0.000000
-->0x00000000 00000000

Classification:

nextafter() is standard Unix; nextafterf() is ANSI (draft)