*Compute a Bessel function of the first kind of order 1*

#include <math.h> double j1( doublex); float j1f( floatx);

`x`- The number that you want to compute the Bessel function for.

- 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 Bessel function for `x` of the first kind of order 1.

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

- Call
`feclearexcept(FE_ALL_EXCEPT)`before calling j1() or j1f(). - On return, if
`fetestexcept(FE_ALL_EXCEPT)`is nonzero, then an error has occurred.

The Bessel value of `x` of the first kind of order 1.

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

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

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

x is NaN |
NaNNaN | — |

The correct result would cause underflow | 0.0 | FE_UNDERFLOW |

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

j1() is POSIX 1003.1 XSI; j1f() is Unix

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

Cancellation point | No |

Interrupt handler | Yes |

Signal handler | Yes |

Thread | Yes |