Add complex math from musl (#422)

libc/tinymath/catan.c

@@ -0,0 +1,144 @@
+/*-*- mode:c;indent-tabs-mode:t;c-basic-offset:8;tab-width:8;coding:utf-8   -*-│
+│vi: set et ft=c ts=8 tw=8 fenc=utf-8                                       :vi│
+╚──────────────────────────────────────────────────────────────────────────────╝
+│                                                                              │
+│  Musl Libc                                                                   │
+│  Copyright © 2005-2014 Rich Felker, et al.                                   │
+│                                                                              │
+│  Permission is hereby granted, free of charge, to any person obtaining       │
+│  a copy of this software and associated documentation files (the             │
+│  "Software"), to deal in the Software without restriction, including         │
+│  without limitation the rights to use, copy, modify, merge, publish,         │
+│  distribute, sublicense, and/or sell copies of the Software, and to          │
+│  permit persons to whom the Software is furnished to do so, subject to       │
+│  the following conditions:                                                   │
+│                                                                              │
+│  The above copyright notice and this permission notice shall be              │
+│  included in all copies or substantial portions of the Software.             │
+│                                                                              │
+│  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,             │
+│  EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF          │
+│  MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.      │
+│  IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY        │
+│  CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,        │
+│  TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE           │
+│  SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                      │
+│                                                                              │
+╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/complex.h"
+#include "libc/math.h"
+#include "libc/tinymath/complex.internal.h"
+
+asm(".ident\t\"\\n\\n\
+Musl libc (MIT License)\\n\
+Copyright 2005-2014 Rich Felker, et. al.\"");
+asm(".include \"libc/disclaimer.inc\"");
+/* clang-format off */
+
+
+/* origin: OpenBSD /usr/src/lib/libm/src/s_catan.c */
+/*
+ * Copyright (c) 2008 Stephen L. Moshier <steve@moshier.net>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+/*
+ *      Complex circular arc tangent
+ *
+ *
+ * SYNOPSIS:
+ *
+ * double complex catan();
+ * double complex z, w;
+ *
+ * w = catan (z);
+ *
+ *
+ * DESCRIPTION:
+ *
+ * If
+ *     z = x + iy,
+ *
+ * then
+ *          1       (    2x     )
+ * Re w  =  - arctan(-----------)  +  k PI
+ *          2       (     2    2)
+ *                  (1 - x  - y )
+ *
+ *               ( 2         2)
+ *          1    (x  +  (y+1) )
+ * Im w  =  - log(------------)
+ *          4    ( 2         2)
+ *               (x  +  (y-1) )
+ *
+ * Where k is an arbitrary integer.
+ *
+ * catan(z) = -i catanh(iz).
+ *
+ * ACCURACY:
+ *
+ *                      Relative error:
+ * arithmetic   domain     # trials      peak         rms
+ *    DEC       -10,+10      5900       1.3e-16     7.8e-18
+ *    IEEE      -10,+10     30000       2.3e-15     8.5e-17
+ * The check catan( ctan(z) )  =  z, with |x| and |y| < PI/2,
+ * had peak relative error 1.5e-16, rms relative error
+ * 2.9e-17.  See also clog().
+ */
+
+
+#define MAXNUM 1.0e308
+
+static const double DP1 = 3.14159265160560607910E0;
+static const double DP2 = 1.98418714791870343106E-9;
+static const double DP3 = 1.14423774522196636802E-17;
+
+static double _redupi(double x)
+{
+	double t;
+	long i;
+
+	t = x/M_PI;
+	if (t >= 0.0)
+		t += 0.5;
+	else
+		t -= 0.5;
+
+	i = t;  /* the multiple */
+	t = i;
+	t = ((x - t * DP1) - t * DP2) - t * DP3;
+	return t;
+}
+
+double complex catan(double complex z)
+{
+	double complex w;
+	double a, t, x, x2, y;
+
+	x = creal(z);
+	y = cimag(z);
+
+	x2 = x * x;
+	a = 1.0 - x2 - (y * y);
+
+	t = 0.5 * atan2(2.0 * x, a);
+	w = _redupi(t);
+
+	t = y - 1.0;
+	a = x2 + (t * t);
+
+	t = y + 1.0;
+	a = (x2 + t * t)/a;
+	w = CMPLX(w, 0.25 * log(a));
+	return w;
+}