1984-07-20 11:03:31 +00:00
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/* $Header$ */
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1984-07-20 10:44:57 +00:00
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#include <pc_err.h>
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extern double _fef();
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extern _trp();
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/*
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log returns the natural logarithm of its floating
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point argument.
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The coefficients are #2705 from Hart & Cheney. (19.38D)
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It calls _fef.
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*/
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#define HUGE 1.701411733192644270e38
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static double log2 = 0.693147180559945309e0;
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static double sqrto2 = 0.707106781186547524e0;
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static double p0 = -.240139179559210510e2;
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static double p1 = 0.309572928215376501e2;
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static double p2 = -.963769093368686593e1;
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static double p3 = 0.421087371217979714e0;
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static double q0 = -.120069589779605255e2;
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static double q1 = 0.194809660700889731e2;
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static double q2 = -.891110902798312337e1;
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double
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_log(arg)
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double arg;
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{
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double x,z, zsq, temp;
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int exp;
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if(arg <= 0) {
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_trp(ELOG);
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return(-HUGE);
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}
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x = _fef(arg,&exp);
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/*
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while(x < 0.5) {
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x =* 2;
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exp--;
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}
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*/
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if(x<sqrto2) {
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x *= 2;
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exp--;
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}
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z = (x-1)/(x+1);
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zsq = z*z;
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temp = ((p3*zsq + p2)*zsq + p1)*zsq + p0;
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temp = temp/(((zsq + q2)*zsq + q1)*zsq + q0);
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temp = temp*z + exp*log2;
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return(temp);
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}
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