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feclearexcept

Defined in header <fenv.h> 
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.

-

Parameters

- -
excepts - bitmask listing the exception flags to clear

Return value

​0​ if all indicated exceptions were successfully cleared or if excepts is zero. Returns a non-zero value on error.

-

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 (!fetestexcept(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

References

See also

- -
-
(C99)
 determines which of the specified floating-point status flags are set
(function)
C++ documentation for feclearexcept
-

- © cppreference.com
Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.
- https://en.cppreference.com/w/c/numeric/fenv/feclearexcept -

-
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