Updated: April 19, 2023 |

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

#include <math.h> double scalb( doublex, doublen);

`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.

This function computes `x` × `r`^{n},
where `r` is the radix
of the machine's floating point arithmetic
and `n` is a finite number. When `r` is 2,
scalb() is equivalent to
ldexp().

Note:
We recommend that you use
scalbn()
because it computes by manipulating exponents, instead of using mock
multiplications or additions.

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

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

`x` * `r`^{n}

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

n isn't an integer |
NaN | FE_INVALID |

x is Inf, and n is Inf |
Inf | — |

x is Inf, and n isn't Inf |
NaN | FE_INVALID |

x isn't Inf, and n is Inf |
Inf, with the sign matching x |
— |

x isn't Inf, and n is -Inf |
0.0, with the sign matching x |
— |

x or n is NaN |
NaN | — |

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 = scalb(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)

Standard Unix; removed from POSIX.1-2008

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

Cancellation point | No |

Interrupt handler | Yes |

Signal handler | Yes |

Thread | Yes |