fpsetmask

FPGETROUND(3)             BSD Library Functions Manual             FPGETROUND(3)

NAME
     fpgetround, fpsetround, fpsetprec, fpgetprec, fpgetmask, fpsetmask,
     fpgetsticky, fpresetsticky — IEEE floating point interface

SYNOPSIS
     #include <ieeefp.h>

     typedef enum {
             FP_RN,          /* round to nearest */
             FP_RM,          /* round down to minus infinity */
             FP_RP,          /* round up to plus infinity */
             FP_RZ           /* truncate */
     } fp_rnd_t;

     fp_rnd_t
     fpgetround(void);

     fp_rnd_t
     fpsetround(fp_rnd_t direction);

     typedef enum {
             FP_PS,          /* 24 bit (single-precision) */
             FP_PRS,         /* reserved */
             FP_PD,          /* 53 bit (double-precision) */
             FP_PE           /* 64 bit (extended-precision) */
     } fp_prec_t;

     fp_prec_t
     fpgetprec(void);

     fp_prec_t
     fpsetprec(fp_prec_t precision);

     #define fp_except_t     int
     #define FP_X_INV        0x01    /* invalid operation */
     #define FP_X_DNML       0x02    /* denormal */
     #define FP_X_DZ         0x04    /* zero divide */
     #define FP_X_OFL        0x08    /* overflow */
     #define FP_X_UFL        0x10    /* underflow */
     #define FP_X_IMP        0x20    /* (im)precision */
     #define FP_X_STK        0x40    /* stack fault */

     fp_except_t
     fpgetmask(void);

     fp_except_t
     fpsetmask(fp_except_t mask);

     fp_except_t
     fpgetsticky(void);

     fp_except_t
     fpresetsticky(fp_except_t sticky);

DESCRIPTION
     The routines described herein are deprecated.  New code should use the
     functionality provided by fenv(3).

     When a floating point exception is detected, the exception sticky flag is
     set and the exception mask is tested.  If the mask is set, then a trap
     occurs.  These routines allow both setting the floating point exception
     masks, and resetting the exception sticky flags after an exception is
     detected.  In addition, they allow setting the floating point rounding mode
     and precision.

     The fpgetround() function returns the current floating point rounding mode.

     The fpsetround() function sets the floating point rounding mode and returns
     the previous mode.

     The fpgetprec() function returns the current floating point precision.

     The fpsetprec() function sets the floating point precision and returns the
     previous precision.

     The fpgetmask() function returns the current floating point exception
     masks.

     The fpsetmask() function sets the floating point exception masks and
     returns the previous masks.

     The fpgetsticky() function returns the current floating point sticky flags.

     The fpresetsticky() function clears the floating point sticky flags and
     returns the previous flags.

     Sample code which prevents a trap on divide-by-zero:

           fpsetmask(~FP_X_DZ);
           a = 1.0;
           b = 0;
           c = a / b;
           fpresetsticky(FP_X_DZ);
           fpsetmask(FP_X_DZ);

IMPLEMENTATION NOTES
     The fpgetprec() and fpsetprec() functions provide functionality unavailable
     on many platforms.  At present, they are implemented only on the i386 and
     amd64 platforms.  Changing precision is not a supported feature: it may be
     ineffective when code is compiled to take advantage of SSE, and many
     library functions and compiler optimizations depend upon the default
     precision for correct behavior.

SEE ALSO
     fenv(3), isnan(3)

HISTORY
     These routines are based on SysV/386 routines of the same name.

CAVEATS
     After a floating point exception and before a mask is set, the sticky flags
     must be reset.  If another exception occurs before the sticky flags are
     reset, then a wrong exception type may be signaled.

BSD                             December 3, 2010                             BSD