fmod(), fmodf(), fmodl()
QNX SDP8.0C Library ReferenceAPIDeveloper
Compute a residue, using floating-point modular arithmetic
Synopsis:
#include <math.h>
double fmod( double x,
double y );
float fmodf( float x,
float y );
long double fmodl( long double x,
long double y );
Arguments:
- x
- An arbitrary number.
- y
- The modulus.
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.
Note:
Compile your program with the -fno-builtin option to prevent the compiler from using a
built-in version of the function.
Description:
The fmod() and fmodf() functions compute the floating-point residue of x (mod y), which is the remainder of x / y, even if the quotient x / y isn't representable.
To check for error situations, use feclearexcept() and fetestexcept(). For example:
- Call
feclearexcept(FE_ALL_EXCEPT)
before calling fmod(), fmodf(), or fmodl(). - On return, if
fetestexcept(FE_ALL_EXCEPT)
is nonzero, then an error has occurred.
Returns:
The residue, x - (i × y), for some integer i such that, if y is nonzero, the result has the same sign as x and a magnitude less than the magnitude of y.
If: | These functions return: | Errors: |
---|---|---|
x is Inf | NaN | FE_INVALID |
y is 0.0 | NaN | FE_INVALID |
x or y is NaN | NaN | — |
The correct value would cause underflow | 0.0 | — |
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 <math.h>
#include <fenv.h>
#include <stdlib.h>
int main( void )
{
int except_flags;
feclearexcept(FE_ALL_EXCEPT);
printf( "%f\n", fmod( 4.5, 2.0 ) );
except_flags = fetestexcept(FE_ALL_EXCEPT);
if(except_flags) {
/* An error occurred; handle it appropriately. */
}
feclearexcept(FE_ALL_EXCEPT);
printf( "%f\n", fmod( -4.5, 2.0 ) );
except_flags = fetestexcept(FE_ALL_EXCEPT);
if(except_flags) {
/* An error occurred; handle it appropriately. */
}
feclearexcept(FE_ALL_EXCEPT);
printf( "%f\n", fmod( 4.5, -2.0 ) );
except_flags = fetestexcept(FE_ALL_EXCEPT);
if(except_flags) {
/* An error occurred; handle it appropriately. */
}
feclearexcept(FE_ALL_EXCEPT);
printf( "%f\n", fmod( -4.5, -2.0 ) );
except_flags = fetestexcept(FE_ALL_EXCEPT);
if(except_flags) {
/* An error occurred; handle it appropriately. */
}
return EXIT_SUCCESS;
}
produces the output:
0.500000
-0.500000
0.500000
-0.500000
Classification:
Safety: | |
---|---|
Cancellation point | No |
Signal handler | Yes |
Thread | Yes |
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