Updated: April 19, 2023 |

*Load the exponent of a radix-independent floating point number*

#include <math.h> double scalbn ( doublex, intn); float scalbnf ( floatx, intn); long double scalbnl ( long doublex, intn);

`x`- The floating point number that you want to multiply by the exponent.
`n`- The exponent to apply to the radix of the machine's floating-point arithmetic.

- 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 scalbn(), scalbnf(), and scalbnl() functions
compute `x` × r^{n},
where `r` is the radix of the machine's floating-point arithmetic.
The difference between the scalbn* and
scalbln*
functions is the type of the second argument.

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

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

`x` × `r`^{n}

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

x is NaN |
NaN | — |

x is ±0.0 or ±Inf |
x |
— |

n is 0 |
x |
— |

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

The correct value would cause overflow | Inf | FE_OVERFLOW |

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 <inttypes.h> #include <math.h> #include <fenv.h> #include <stdlib.h> int main( void ) { double a, b, c, d; int except_flags; feclearexcept(FE_ALL_EXCEPT); a = 10; b = 2; c = scalbn(a, b); except_flags = fetestexcept(FE_ALL_EXCEPT); if(except_flags) { /* An error occurred; handle it appropriately. */ } feclearexcept(FE_ALL_EXCEPT); d = sqrt(c/a); except_flags = fetestexcept(FE_ALL_EXCEPT); if(except_flags) { /* An error occurred; handle it appropriately. */ } printf("Radix of machine's fp arithmetic is %f \n", d); printf("So %f = %f * (%f ^ %f) \n", c, a, d, b); return EXIT_SUCCESS; }

produces the output:

Radix of machine's fp arithmetic is 2.000000 So 40.000000 = 10.000000 * (2.000000 ^ 2.000000)

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

Cancellation point | No |

Interrupt handler | Yes |

Signal handler | Yes |

Thread | Yes |