46 lines
1.1 KiB
C
46 lines
1.1 KiB
C
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/*
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* ====================================================
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* Copyright (C) 1998 by Cygnus Solutions. All rights reserved.
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*
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* Permission to use, copy, modify, and distribute this
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* software is freely granted, provided that this notice
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* is preserved.
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* ====================================================
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*/
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/*
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Fast version of exp using Intel float instructions.
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double _f_exp (double x);
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Function computes e ** x. The following special cases exist:
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1. if x is 0.0 ==> return 1.0
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2. if x is infinity ==> return infinity
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3. if x is -infinity ==> return 0.0
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4. if x is NaN ==> return x
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There is no error checking or setting of errno.
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*/
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#include <math.h>
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#include <ieeefp.h>
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#include "f_math.h"
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double _f_exp (double x)
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{
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if (check_finite(x))
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{
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double result;
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asm ("fldl2e; fmulp; fld %%st; frndint; fsub %%st,%%st(1); fxch;" \
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"fchs; f2xm1; fld1; faddp; fxch; fld1; fscale; fstp %%st(1); fmulp" :
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"=t"(result) : "0"(x));
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return result;
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}
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else if (x == -infinity())
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return 0.0;
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return x;
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}
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