feclearexcept - cppreference.com (original) (raw)
| | | | | --------------------------------- | | ----------- | | int feclearexcept( int excepts ); | | (since C99) |
Attempts to clear the floating-point exceptions that are listed in the bitmask argument excepts, which is a bitwise OR of the floating-point exception macros.
[edit] Parameters
| excepts | - | bitmask listing the exception flags to clear |
|---|
[edit] Return value
0 if all indicated exceptions were successfully cleared or if excepts is zero. Returns a non-zero value on error.
[edit] Example
#include <fenv.h> #include <stdio.h> #include <math.h> #include <float.h> /*
- A possible implementation of hypot which makes use of many advanced
- floating-point features.
*/
double hypot_demo(double a, double b) {
const int range_problem = FE_OVERFLOW | FE_UNDERFLOW;
feclearexcept(range_problem);
// try a fast algorithm
double result = sqrt(a * a + b * b);
if (
(range_problem)) // no overflow or underflow return result; // return the fast result // do a more complicated calculation to avoid overflow or underflow int a_exponent,b_exponent; frexp(a, &a_exponent); frexp(b, &b_exponent);
if (a_exponent - b_exponent > DBL_MAX_EXP) return fabs(a) + fabs(b); // we can ignore the smaller value // scale so that fabs(a) is near 1 double a_scaled = scalbn(a, -a_exponent); double b_scaled = scalbn(b, -a_exponent); // overflow and underflow is now impossible result = sqrt(a_scaled * a_scaled + b_scaled * b_scaled); // undo scaling return scalbn(result, a_exponent); } int main(void) { // Normal case takes the fast route printf("hypot(%f, %f) = %f\n", 3.0, 4.0, hypot_demo(3.0, 4.0)); // Extreme case takes the slow but more accurate route printf("hypot(%e, %e) = %e\n", DBL_MAX / 2.0, DBL_MAX / 2.0, hypot_demo(DBL_MAX / 2.0, DBL_MAX / 2.0)); return 0; }
Output:
hypot(3.000000, 4.000000) = 5.000000 hypot(8.988466e+307, 8.988466e+307) = 1.271161e+308
[edit] References
C11 standard (ISO/IEC 9899:2011):
7.6.2.1 The feclearexcept function (p: 209)
C99 standard (ISO/IEC 9899:1999):
7.6.2.1 The feclearexcept function (p: 190)