Updated: April 19, 2023 |

*Log(1+x)*

#include <math.h> double log1p ( doublex); float log1pf ( floatx); long double log1pl( long doublex);

`x`- The number that you want to add 1 to and compute the natural log of.

- 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 log1p(), log1pf(), and log1pl()
functions compute the value of
log(1+`x`),
where `x` > -1.0.

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

- Call
`feclearexcept(FE_ALL_EXCEPT)`before calling log1p(), log1pf(), or log1pl(). - On return, if
`fetestexcept(FE_ALL_EXCEPT)`is nonzero, then an error has occurred.

log(1+`x`)

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

x is -1.0 |
-Inf | FE_DIVBYZERO |

Less than -1.0 and finite, or -Inf | NaN | FE_INVALID |

±0.0 | x |
— |

Inf | Inf | — |

NaN | NaN | — |

Subnormal | x |
— |

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 |