以下示例演示如何确定早期计算引起的浮点异常。会将系统 include 文件 floatingpoint.h 中定义的位屏蔽应用于 ieee_flags 的返回值。
在以下示例(即 DetExcFlg.F)中,include 文件是使用 #include 预处理程序指令引入的,这就要求以 .F 后缀命名源文件。下溢是由最小的双精度数除以 2 引起的。
示例:使用 ieee_flags 检测异常,然后对其进行解码:
#include "floatingpoint.h"
CHARACTER*16 out
DOUBLE PRECISION d_max_subnormal, x
INTEGER div, flgs, inv, inx, over, under
x = d_max_subnormal() / 2.0 ! Cause underflow
flgs=ieee_flags(’get’,’exception’,’’,out) ! Which are raised?
inx = and(rshift(flgs, fp_inexact) , 1) ! Decode
div = and(rshift(flgs, fp_division) , 1) ! the value
under = and(rshift(flgs, fp_underflow), 1) ! returned
over = and(rshift(flgs, fp_overflow) , 1) ! by
inv = and(rshift(flgs, fp_invalid) , 1) ! ieee_flags
PRINT *, "Highest priority exception is: ", out
PRINT *, ’ invalid divide overflo underflo inexact’
PRINT ’(5i8)’, inv, div, over, under, inx
PRINT *, ’(1 = exception is raised; 0 = it is not)’
i = ieee_flags(’clear’, ’exception’, ’all’, out) ! Clear all
END
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示例:编译并运行上述示例 (DetExcFlg.F):
demo% f95 DetExcFlg.F
demo% a.out
Highest priority exception is: underflow
invalid divide overflo underflo inexact
0 0 0 1 1
(1 = exception is raised; 0 = it is not)
demo%
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