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- /*
- * (c) copyright 1988 by the Vrije Universiteit, Amsterdam, The Netherlands.
- * See the copyright notice in the ACK home directory, in the file "Copyright".
- *
- * Author: Ceriel J.H. Jacobs
- */
- /* $Id$ */
- #define __NO_DEFS
- #include <math.h>
- #include <pc_err.h>
- #if __STDC__
- #include <pc_math.h>
- #include <float.h>
- #endif
- #undef HUGE
- #define HUGE 1e1000
- double
- _log(x)
- double x;
- {
- /* Algorithm and coefficients from:
- "Software manual for the elementary functions"
- by W.J. Cody and W. Waite, Prentice-Hall, 1980
- */
- static double a[] = {
- -0.64124943423745581147e2,
- 0.16383943563021534222e2,
- -0.78956112887491257267e0
- };
- static double b[] = {
- -0.76949932108494879777e3,
- 0.31203222091924532844e3,
- -0.35667977739034646171e2,
- 1.0
- };
- extern double _fef();
- double znum, zden, z, w;
- int exponent;
- if (x <= 0) {
- _trp(ELOG);
- return -HUGE;
- }
- x = _fef(x, &exponent);
- if (x > M_1_SQRT2) {
- znum = (x - 0.5) - 0.5;
- zden = x * 0.5 + 0.5;
- }
- else {
- znum = x - 0.5;
- zden = znum * 0.5 + 0.5;
- exponent--;
- }
- z = znum/zden; w = z * z;
- x = z + z * w * (POLYNOM2(w,a)/POLYNOM3(w,b));
- z = exponent;
- x += z * (-2.121944400546905827679e-4);
- return x + z * 0.693359375;
- }
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