nexttoward(), nexttowardf(), nexttowardl()

Arguments:

x

The number for which you want the next number in the specified direction.

y

A number that specifies the direction you want to go; see below.

Library:

libm

The general-purpose math library.

libm-sve

A library that optimizes the code for ARMv8.2 chips that have Scalable Vector Extension hardware.

Your system requirements will determine how you should work with these libraries:

• If you want only selected processes to run with the SVE version, you can include both libraries in your OS image and use the -l m or -l m-sve option to qcc to link explicitly against the appropriate one.
• If you want all processes to use the SVE version, include libm-sve.so in your OS image and set up a symbolic link from libm.so to libm-sve.so. Use the -l m option to qcc to link against the library.

Description:

The nexttoward(), nexttowardf(), and nexttowardl() functions compute the next representable double-precision floating-point value following x in the direction of y. These functions are equivalent to nextafter(), nextafterf(), and nextafterl(), respectively, except that:

• the second argument is of type long double
• if x equals y, nexttoward(), nexttowardf(), and nexttowardl() return y converted to the type of the function.

To check for error situations, use feclearexcept() and fetestexcept(). For example:

• Call feclearexcept(FE_ALL_EXCEPT) before calling nexttoward(), nexttowardf(), or nexttowardl().
• On return, if fetestexcept(FE_ALL_EXCEPT) is nonzero, then an error has occurred.

Returns:

The next machine floating-point number of x in the direction towards y, converted to the type that the function returns.

These functions raise FE_INEXACT if the FPU reports that the result can't be exactly represented as a floating-point number.

Examples:

#include <stdio.h>
#include <inttypes.h>
#include <math.h>
#include <fenv.h>
#include <stdlib.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;
    int except_flags;

    a = 0;

    feclearexcept(FE_ALL_EXCEPT);
    b = nexttoward(a, -1);
    except_flags = fetestexcept(FE_ALL_EXCEPT);
    if(except_flags) {
        /* An error occurred; handle it appropriately. */
    }

    feclearexcept(FE_ALL_EXCEPT);
    c = nexttoward(a, 1);
    except_flags = fetestexcept(FE_ALL_EXCEPT);
    if(except_flags) {
        /* An error occurred; handle it appropriately. */
    }

    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 EXIT_SUCCESS;
}

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:

C11, POSIX 1003.1