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+/* $OpenBSD: s_ctanl.c,v 1.3 2011/07/20 21:02:51 martynas Exp $ */
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+
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+/*
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+ * Copyright (c) 2008 Stephen L. Moshier <steve@moshier.net>
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+ *
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+ * Permission to use, copy, modify, and distribute this software for any
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+ * purpose with or without fee is hereby granted, provided that the above
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+ * copyright notice and this permission notice appear in all copies.
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+ *
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+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
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+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
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+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
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+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
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+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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+ */
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+
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+/* ctanl()
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+ *
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+ * Complex circular tangent
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+ *
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+ *
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+ *
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+ * SYNOPSIS:
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+ *
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+ * long double complex ctanl();
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+ * long double complex z, w;
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+ *
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+ * w = ctanl( z );
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+ *
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+ *
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+ *
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+ * DESCRIPTION:
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+ *
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+ * If
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+ * z = x + iy,
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+ *
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+ * then
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+ *
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+ * sin 2x + i sinh 2y
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+ * w = --------------------.
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+ * cos 2x + cosh 2y
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+ *
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+ * On the real axis the denominator is zero at odd multiples
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+ * of PI/2. The denominator is evaluated by its Taylor
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+ * series near these points.
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+ *
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+ *
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+ * ACCURACY:
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+ *
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+ * Relative error:
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+ * arithmetic domain # trials peak rms
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+ * DEC -10,+10 5200 7.1e-17 1.6e-17
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+ * IEEE -10,+10 30000 7.2e-16 1.2e-16
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+ * Also tested by ctan * ccot = 1 and catan(ctan(z)) = z.
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+ */
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+
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+#include <complex.h>
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+#include <float.h>
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+#include <math.h>
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+
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+#if LDBL_MANT_DIG == 64
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+static const long double MACHEPL= 5.42101086242752217003726400434970855712890625E-20L;
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+#elif LDBL_MANT_DIG == 113
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+static const long double MACHEPL = 9.629649721936179265279889712924636592690508e-35L;
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+#endif
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+
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+static const long double PIL = 3.141592653589793238462643383279502884197169L;
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+static const long double DP1 = 3.14159265358979323829596852490908531763125L;
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+static const long double DP2 = 1.6667485837041756656403424829301998703007e-19L;
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+static const long double DP3 = 1.8830410776607851167459095484560349402753e-39L;
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+
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+static long double
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+redupil(long double x)
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+{
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+ long double t;
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+ long i;
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+
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+ t = x / PIL;
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+ if (t >= 0.0L)
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+ t += 0.5L;
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+ else
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+ t -= 0.5L;
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+
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+ i = t; /* the multiple */
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+ t = i;
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+ t = ((x - t * DP1) - t * DP2) - t * DP3;
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+ return (t);
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+}
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+
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+static long double
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+ctansl(long double complex z)
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+{
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+ long double f, x, x2, y, y2, rn, t;
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+ long double d;
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+
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+ x = fabsl(2.0L * creall(z));
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+ y = fabsl(2.0L * cimagl(z));
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+
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+ x = redupil(x);
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+
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+ x = x * x;
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+ y = y * y;
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+ x2 = 1.0L;
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+ y2 = 1.0L;
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+ f = 1.0L;
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+ rn = 0.0L;
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+ d = 0.0L;
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+ do {
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+ rn += 1.0L;
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+ f *= rn;
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+ rn += 1.0L;
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+ f *= rn;
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+ x2 *= x;
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+ y2 *= y;
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+ t = y2 + x2;
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+ t /= f;
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+ d += t;
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+
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+ rn += 1.0L;
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+ f *= rn;
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+ rn += 1.0L;
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+ f *= rn;
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+ x2 *= x;
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+ y2 *= y;
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+ t = y2 - x2;
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+ t /= f;
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+ d += t;
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+ }
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+ while (fabsl(t/d) > MACHEPL);
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+ return(d);
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+}
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+
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+long double complex
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+ctanl(long double complex z)
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+{
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+ long double complex w;
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+ long double d, x, y;
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+
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+ x = creall(z);
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+ y = cimagl(z);
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+ d = cosl(2.0L * x) + coshl(2.0L * y);
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+
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+ if (fabsl(d) < 0.25L) {
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+ d = fabsl(d);
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+ d = ctansl(z);
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+ }
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+ if (d == 0.0L) {
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+ /*mtherr( "ctan", OVERFLOW );*/
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+ w = LDBL_MAX + LDBL_MAX * I;
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+ return (w);
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+ }
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+
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+ w = sinl(2.0L * x) / d + (sinhl(2.0L * y) / d) * I;
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+ return (w);
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+}
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