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See FLP03-C. Detect and handle floating-point errors for more details on how to detect floating-point errors.

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Denormalized Numbers

Certain functions may produce range errors specifically when applied with a denormal argumentdenormalized number. These functions are: asin(), asinh(), atan(), atanh(), and erf(). When evaluated with a denormal argumentdenormalized number, these functions can produce an inexact, denormal valuedenormalized value, which is an underflow error. Subclause 7.12.1, paragraph 6, of the C Standard [ISO/IEC 9899:2011] defines the following behavior for floating-point underflow:

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If denormal results denormalized results are supported, the returned value is exact and there will not be a range error. When dealing with fmod(), subclause F.10.7.1, paragraph 2, of the C Standard [ISO/IEC 9899:2011] states:

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Subclause F.10.7.2, paragraph 2, and subclause F.10.7.3, paragraph 2 of the C Standard [ISO/IEC 9899:2011] cover remainder() and remquo() for when denormal results denormalized results are supported.

Noncompliant Code Example (sqrt())

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#include <errno.h>
#include <math.h>
#if defined(math_errhandling) \
  && (math_errhandling & MATH_ERREXCEPT)
#include <fenv.h>

#pragma STDC FENV_ACCESS ON
#endif

void func(double x, double y) {
  #if defined(math_errhandling) \
    && (math_errhandling & MATH_ERREXCEPT)
    feclearexcept(FE_ALL_EXCEPT);
  #endif
  errno = 0;

  double result;

  if (((x == 0.0f) && islessequal(y, 0.0)) || isless(x, 0.0)) {
    /* Handle domain or pole error */
  }

  result = pow(x, y);

  #if !defined(math_errhandling) \
    || (math_errhandling & MATH_ERRNO)
  if (errno != 0) {
    /* Handle range error */
  }
  #endif
  #if defined(math_errhandling) \
    && (math_errhandling & MATH_ERREXCEPT)
  if (fetestexcept(FE_INVALID
                 | FE_DIVBYZERO
                 | FE_OVERFLOW
                 | FE_UNDERFLOW) != 0) {
    /* Handle range error */
  }
  #endif
}

Noncompliant Code Example (asin(),

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Denormalized Number)

This noncompliant code example determines the arcsin of x:

#include <math.h>
 
void func(float x) {
  float result = asin(x);
  /* ... */
}

Compliant Soluction (asin(),

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Denormalized Number)

Because this function has no domain errors but may have range errors, the programmer must detect a range error and act accordingly:

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