Load the exponent of a radix-independent floating point number
#include <math.h> double scalb( double x, double n );
This function computes x × rn, 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().
To check for error situations, use feclearexcept() and fetestexcept(). For example:
x * rn
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 | No |
Signal handler | No |
Thread | Yes |