pow(), powf(), powl()

Synopsis:

#include <math.h>

double pow( double x, 
            double y );

float powf( float x, 
            float y );

long double powl( long double x,
                  long double y );

Arguments:

x: The number you want to raise.
y: The power you want to raise the number to.

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 pow(), powf(), and powl() functions compute x raised to the power of y.

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

Call feclearexcept(FE_ALL_EXCEPT) before calling pow(), powf(), or powl().
On return, if fetestexcept(FE_ALL_EXCEPT) is nonzero, then an error has occurred.

Returns:

The value of x^y.


If `x` is:	And `y` is:	These functions return:	Errors:
< 0.0, but finite	Finite non-integer	NaN	FE_INVALID
0.0	< 0.0	Inf	FE_DIVBYZERO
1.0	Any value, including NaN	1.0	—
Not 1.0	NaN	NaN	—
Any value, including 0.0 and NaN	±0.0	1.0, but note that the correct mathematical result for 0.0^0.0 is undefined	—
NaN	Nonzero	NaN	—
±0.0	Any odd integer > 0.0	0.0, with the same sign as `x`	—
±0.0	Any even integer > 0.0	0.0	—
-1.0	±Inf	1.0	—
\|`x`\| < 1.0	-Inf	Inf	—
\|`x`\| > 1.0	-Inf	0.0	—
\|`x`\| < 1.0	Inf	0.0	—
\|`x`\| > 1.0	Inf	Inf	—
-Inf	An odd integer < 0.0	-0.0	—
-Inf	A non-odd integer < 0.0	+0.0	—
-Inf	An odd integer > 0.0	-Inf	—
-Inf	A non-odd integer > 0.0	Inf	—
Inf	< 0.0	0.0	—
Inf	> 0.0	Inf	—


If the correct value would cause:	These functions return:	Errors:
Overflow	Inf	FE_OVERFLOW
Underflow and is representable	The correct value, after rounding	FE_UNDERFLOW

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", pow( 1.5, 2.5 ) );

    except_flags = fetestexcept(FE_ALL_EXCEPT);
    if(except_flags) {
        /* An error occurred; handle it appropriately. */
    }

    return EXIT_SUCCESS;
}

produces the output:

2.755676

Classification:

C11, POSIX 1003.1


Safety:
Cancellation point	No
Signal handler	Yes
Thread	Yes