Floating point operations

Rounding control

The floating point arithmetic provides four rounding modes that affect the result of most floating point operations. (These modes are defined in the header ieeefp.h):

FP_RN round to nearest representable number, tie -> even
FP_RP round toward plus infinity
FP_RM round toward minus infinity
FP_RZ round toward zero (truncate)

You can check the current rounding mode with the function

   fp_rnd fpgetround(void); /* return current rounding mode */

You can change the rounding mode for floating point operations with the function:

   fp_rnd fpsetround(fp_rnd); /* set rounding mode, */
                              /* return previous    */

(fp_rnd is an enumeration type with the enumeration constants listed and described above. The values for these constants are in ieeefp.h.)

NOTE: The examples in this section, such as the one directly above, illustrate function prototypes. For further information on function prototypes, see ``Function definitions''.

The default rounding mode is round-to-nearest. In C, floating point to integer conversions are always done by truncation, and the current rounding mode has no effect on these operations.

For more information on fpgetround and fpsetround, see fpgetround(S).