modf(), modff(), modfl()

Break a number into integral and fractional parts

Synopsis:

#include <math.h>

double modf( double value,
             double* iptr );

float modff( float value,
             float* iptr );

long double modfl( long double value,
                   long double* iptr );

Arguments:

value: The value that you want to break into parts.
iptr: A pointer to a location where the function can store the integral part of the number.

Library:

libm: The general-purpose math library.
libm-sve: (QNX Neutrino 7.1 or later) 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.

Note: Compile your program with the -fno-builtin option to prevent the compiler from using a built-in version of the function.

Description:

The modf(), modff(), and modfl() functions break the given value into integral and fractional parts, each of which has the same sign as the argument. They store the integral part in the object pointed to by iptr.

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

Call feclearexcept(FE_ALL_EXCEPT) before calling modf(), modff(), or modfl().
On return, if fetestexcept(FE_ALL_EXCEPT) is nonzero, then an error has occurred.

Returns:

The signed fractional part of value.

If `value` is:	These functions return:	And set *`iptr` to:	Errors:
±Inf	0.0, with the same sign as `value`	Inf, with the same sign as `value`	—
NaN	NaN	NaN	—

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 <stdlib.h>
#include <math.h>

int main( void )
{
    double integral_value, fractional_part;

    fractional_part = modf( 4.5, &integral_value );
    printf( "%f %f\n", fractional_part, integral_value );
    
    fractional_part = modf( -4.5, &integral_value );
    printf( "%f %f\n", fractional_part, integral_value );
    
    return EXIT_SUCCESS;
}

produces the output:

0.500000 4.000000
-0.500000 -4.000000

Classification:

C11, POSIX 1003.1

Safety:
Cancellation point	No
Interrupt handler	Yes
Signal handler	Yes
Thread	Yes