5.78 <fenv.h> floating-point environment access in C99

The C99 standard header file <fenv.h> provides access to an IEEE 754-compliant floating-point environment for numerical programming.

The library introduces two types and numerous macros and functions for managing and controlling floating-point state.

The new types supported are:

  • fenv_t, representing the entire floating-point environment.

  • fexcept_t, representing the floating-point state.

New macros supported include:

  • FE_DIVBYZERO, FE_INEXACT, FE_INVALID, FE_OVERFLOW and FE_UNDERFLOW for managing floating-point exceptions.

  • FE_DOWNWARD, FE_TONEAREST, FE_TOWARDZERO, FE_UPWARD for managing rounding in the represented rounding direction.

  • FE_DFL_ENV, representing the default floating-point environment.

New functions include:

int feclearexcept(int ex); // clear floating-point exceptions selected by ex
int feraiseexcept(int ex); // raise floating point exceptions selected by ex
int fetestexcept(int ex); // test floating point exceptions selected by ex
int fegetround(void); // return the current rounding mode
int fesetround(int mode); // set the current rounding mode given by mode
int fegetenv(fenv_t *penv); return the floating-point environment in penv
int fesetenv(const fenv_t *penv); // set the floating-point environment to penv
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