Updated: April 19, 2023 |

*Compute the complex natural (base- e) logarithm of a complex number*

#include <complex.h> double complex clog(double complexz); float complex clogf(float complexz); long double complex clogl(long double complexz);

`z`- The complex value that you want to compute the complex natural logarithm 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.

These functions compute the complex natural (base-`e`) logarithm of the complex number specified
by `z` with a branch cut along the negative real axis.
The natural logarithm of a complex number `z` with polar coordinate components
(`r`,θ) equals ln `r` +
`i`(θ+2`n``π`), with the principal value
ln `r` + `i`θ.

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

- Call
`feclearexcept(FE_ALL_EXCEPT)`before calling clog(), clogf(), or clogl(). - On return, if
`fetestexcept(FE_ALL_EXCEPT)`is nonzero, then an error has occurred.

If no errors occur, the complex natural logarithm of `z`, in the range of a strip in the
interval [−i`π`, +i`π`] along the imaginary axis and mathematically unbounded along the real axis.

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

-0 + 0i |
-Inf + πi |
FE_DIVBYZERO |

0 + 0i |
-Inf + 0i |
FE_DIVBYZERO |

x + Infi, for any finite x |
Inf + (π/2)i |
— |

x + NaNi, for any finite x |
NaN + NaNi |
— |

-Inf + yi, for any finite positive y |
-Inf + πi |
— |

Inf + yi, for any finite positive y |
-Inf + 0i |
— |

-Inf + Infi |
Inf + (3π/4)i |
— |

Inf + Infi |
Inf + (π/4)i |
— |

±Inf + NaNi |
Inf + NaNi |
— |

NaN + yi, for any finite y |
NaN + NaNi |
— |

NaN + Infi |
NaN + NaNi |
— |

NaN + NaNi |
NaN + NaNi |
— |

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 |