Updated: April 19, 2023 |

*Raise a number to a given power*

#include <math.h> double pow( doublex, doubley); float powf( floatx, floaty); long double powl( long doublex, long doubley);

`x`- The number you want to raise.
`y`- The power you want to raise the number to.

- 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.

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.

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.

#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

Safety: | |
---|---|

Cancellation point | No |

Interrupt handler | Yes |

Signal handler | Yes |

Thread | Yes |