Updated: April 19, 2023 |

*Compute the error function of a number*

#include <math.h> double erf ( doublex); float erff ( floatx); long double erfl ( long doublex);

`x`- The number for which you want to compute the error function.

- 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 erf(), erff(), and erfl()
functions compute the following:

If `x` is large and the result of
erf() is subtracted from `1.0`,
the results aren't very accurate; use
erfc() instead.

This equality is true: erf(-`x`) = -erf(`x`)

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

- Call
`feclearexcept(FE_ALL_EXCEPT)`before calling erf(), erff(), or erfl(). - On return, if
`fetestexcept(FE_ALL_EXCEPT)`is nonzero, then an error has occurred.

The value of the error function.

If x is: |
These functions return: | Errors: |
---|---|---|

±0.0 | 0.0, with the same sign as x |
— |

A value that would cause underflow | x |
FE_UNDERFLOW |

±Inf | 1.0, with the same sign as x |
— |

NaN | NaN | — |

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

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

Cancellation point | No |

Interrupt handler | Yes |

Signal handler | Yes |

Thread | Yes |