Updated: April 19, 2023 |

*Break a floating-point number into a normalized fraction and an integral power of 2*

#include <math.h> double frexp( doublevalue, int*exp); float frexpf( floatvalue, int*exp); long double frexp( long doublevalue, int*exp);

`value`- The value you want to break into a normalized fraction.
`exp`- A pointer to a location where the function can store the integral power of 2.

- 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 break a floating-point number into a
normalized fraction and an integral power of 2.
It stores the integral power of 2 in the int pointed to by
`exp`.

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

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

A number, `x`, that has a magnitude in the interval
[0.5, 1.0] or is 0.0, such that `value` = `x` * 2^{exp}.

If value is: |
These functions return: | *exp |
Errors: |
---|---|---|---|

±0.0 | 0.0, with the same sign as value |
0 | — |

±Inf | value |
Unspecified | — |

NaN | value |
Unspecified | — |

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 <stdlib.h> #include <math.h> #include <fenv.h> int main( void ) { int expon; double value; int except_flags; feclearexcept(FE_ALL_EXCEPT); value = frexp( 4.25, &expon ); printf( "%f %d\n", value, expon ); except_flags = fetestexcept(FE_ALL_EXCEPT); if(except_flags) { /* An error occurred; handle it appropriately. */ } feclearexcept(FE_ALL_EXCEPT); value = frexp( -4.25, &expon ); printf( "%f %d\n", value, expon ); except_flags = fetestexcept(FE_ALL_EXCEPT); if(except_flags) { /* An error occurred; handle it appropriately. */ } return EXIT_SUCCESS; }

produces the output:

0.531250 3 -0.531250 3

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

Cancellation point | No |

Interrupt handler | Yes |

Signal handler | Yes |

Thread | Yes |