XL Fortran Enterprise Edition for AIX : User's Guide - IBM

lock data
include ’fpdc.h’
include ’fpdt.h’
end
XL Fortran also provides several procedures that allow you to control the
floating-point status and control register of the processor directly. These procedures
are more efficient than the fpsets and fpgets subroutines because they are mapped
into inlined machine instructions that manipulate the floating-point status and
control register (fpscr) directly.
XL Fortran supplies the get_round_mode() and set_round_mode() procedures in
the xlf_fp_util module. These procedures return and set the current floating-point
rounding mode, respectively.
For example:
program fptest
use, intrinsic :: xlf_fp_util
integer(fpscr_kind) old_fpscr
if ( get_round_mode() == fp_rnd_rn ) then
print *, ’Before test: Rounding mode is towards nearest’
print *, ’ 2.0 / 3.0 = ’, 2.0 / 3.0
print *, ’ -2.0 / 3.0 = ’, -2.0 / 3.0
end if
old_fpscr = set_round_mode( fp_rnd_rp )
r = 2.0 / 3.0
print *, ’Round towards +infinity: 2.0 / 3.0 = ’, r
old_fpscr = set_round_mode( fp_rnd_rm )
r = -2.0 / 3.0
print *, ’Round towards -infinity: -2.0 / 3.0 = ’, r
end
XL Fortran supplies the ieee_get_rounding_mode() and ieee_set_rounding_mode()
procedures in the ieee_arithmetic module. These portable procedures retrieve and
set the current floating-point rounding mode, respectively.
For example:
program fptest
use, intrinsic :: ieee_arithmetic
type(ieee_round_type) current_mode
call ieee_get_rounding_mode( current_mode )
if ( current_mode == ieee_nearest ) then
print *, ’Before test: Rounding mode is towards nearest’
print *, ’ 2.0 / 3.0 = ’, 2.0 / 3.0
print *, ’ -2.0 / 3.0 = ’, -2.0 / 3.0
end if
call ieee_set_rounding_mode( ieee_up )
r = 2.0 / 3.0
print *, ’Round towards +infinity: 2.0 / 3.0 = ’, r
call ieee_set_rounding_mode( ieee_down )
r = -2.0 / 3.0
print *, ’Round towards -infinity: -2.0 / 3.0 = ’, r
end
Notes:
1. Extended-precision floating-point values must only be used in round-to-nearest
mode.
XL Fortran Floating-Point Processing 293