Updated: April 19, 2023 |

*Load exponent: multiply a floating-point number by an integral power of 2*

#include <math.h> double ldexp( doublex, intexp); float ldexp( floatx, intexp); long double ldexpl( long doublex, intexp);

`x`- A floating-point number.
`exp`- The exponent of 2 to multiply
`x`by.

- 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 multiply the floating-point number
`x` by
2^{exp}.

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

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

`x` * 2^{exp}

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

x is ±0.0 |
x |
— |

x is ±Inf |
x |
— |

x is NaN |
x |
— |

The result would cause overflow | Inf | FE_OVERFLOW |

The correct value would cause underflow | The correct value, after rounding | — |

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 <math.h> #include <fenv.h> #include <stdlib.h> int main( void ) { int except_flags; double value; feclearexcept(FE_ALL_EXCEPT); value = ldexp( 4.7072345, 5 ); except_flags = fetestexcept(FE_ALL_EXCEPT); if(except_flags) { /* An error occurred; handle it appropriately. */ } printf( "%f\n", value ); return EXIT_SUCCESS; }

produces the output:

150.631504

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

Cancellation point | No |

Interrupt handler | Yes |

Signal handler | Yes |

Thread | Yes |