46 lines
826 B
C
46 lines
826 B
C
/*
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* (c) copyright 1988 by the Vrije Universiteit, Amsterdam, The Netherlands.
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* See the copyright notice in the ACK home directory, in the file "Copyright".
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*
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* Author: Ceriel J.H. Jacobs
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*/
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/* $Header$ */
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#include <math.h>
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#include <errno.h>
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extern int errno;
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double
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atan2(y, x)
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double x, y;
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{
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extern double atan();
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double absx, absy, val;
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if (x == 0 && y == 0) {
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errno = EDOM;
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return 0;
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}
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absy = y < 0 ? -y : y;
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absx = x < 0 ? -x : x;
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if (absy - absx == absy) {
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/* x negligible compared to y */
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return y < 0 ? -M_PI_2 : M_PI_2;
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}
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if (absx - absy == absx) {
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/* y negligible compared to x */
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val = 0.0;
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}
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else val = atan(y/x);
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if (x > 0) {
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/* first or fourth quadrant; already correct */
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return val;
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}
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if (y < 0) {
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/* third quadrant */
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return val - M_PI;
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}
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return val + M_PI;
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}
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