50 lines
1.3 KiB
C
50 lines
1.3 KiB
C
/*
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* This file is part of the UCB release of Plan 9. It is subject to the license
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* terms in the LICENSE file found in the top-level directory of this
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* distribution and at http://akaros.cs.berkeley.edu/files/Plan9License. No
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* part of the UCB release of Plan 9, including this file, may be copied,
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* modified, propagated, or distributed except according to the terms contained
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* in the LICENSE file.
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*/
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/*
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exp returns the exponential function of its
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floating-point argument.
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The coefficients are #1069 from Hart and Cheney. (22.35D)
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*/
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#include <u.h>
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#include <libc.h>
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#define p0 .2080384346694663001443843411e7
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#define p1 .3028697169744036299076048876e5
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#define p2 .6061485330061080841615584556e2
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#define q0 .6002720360238832528230907598e7
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#define q1 .3277251518082914423057964422e6
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#define q2 .1749287689093076403844945335e4
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#define log2e 1.4426950408889634073599247
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#define sqrt2 1.4142135623730950488016887
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#define maxf 10000
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double
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jehanne_exp(double arg)
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{
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double fract, temp1, temp2, xsq;
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int ent;
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if(arg == 0)
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return 1;
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if(arg < -maxf)
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return 0;
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if(arg > maxf)
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return jehanne_Inf(1);
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arg *= log2e;
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ent = jehanne_floor(arg);
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fract = (arg-ent) - 0.5;
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xsq = fract*fract;
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temp1 = ((p2*xsq+p1)*xsq+p0)*fract;
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temp2 = ((xsq+q2)*xsq+q1)*xsq + q0;
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return jehanne_ldexp(sqrt2*(temp2+temp1)/(temp2-temp1), ent);
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}
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