first commit of the new libm!

thanks to the hard work of Szabolcs Nagy (nsz), identifying the best
(from correctness and license standpoint) implementations from freebsd
and openbsd and cleaning them up! musl should now fully support c99
float and long double math functions, and has near-complete complex
math support. tgmath should also work (fully on gcc-compatible
compilers, and mostly on any c99 compiler).

based largely on commit 0376d44a890fea261506f1fc63833e7a686dca19 from
nsz's libm git repo, with some additions (dummy versions of a few
missing long double complex functions, etc.) by me.

various cleanups still need to be made, including re-adding (if
they're correct) some asm functions that were dropped.

1 files changed, 119 insertions, 0 deletions

diff --git a/src/math/atan2.c b/src/math/atan2.c
new file mode 100644
index 00000000..3c35fbf0
--- /dev/null
+++ b/src/math/atan2.c
@@ -0,0 +1,119 @@
+/* origin: FreeBSD /usr/src/lib/msun/src/e_atan2.c */
+/*
+ * ====================================================
+ * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
+ *
+ * Developed at SunSoft, a Sun Microsystems, Inc. business.
+ * Permission to use, copy, modify, and distribute this
+ * software is freely granted, provided that this notice
+ * is preserved.
+ * ====================================================
+ *
+ */
+/* atan2(y,x)
+ * Method :
+ *      1. Reduce y to positive by atan2(y,x)=-atan2(-y,x).
+ *      2. Reduce x to positive by (if x and y are unexceptional):
+ *              ARG (x+iy) = arctan(y/x)           ... if x > 0,
+ *              ARG (x+iy) = pi - arctan[y/(-x)]   ... if x < 0,
+ *
+ * Special cases:
+ *
+ *      ATAN2((anything), NaN ) is NaN;
+ *      ATAN2(NAN , (anything) ) is NaN;
+ *      ATAN2(+-0, +(anything but NaN)) is +-0  ;
+ *      ATAN2(+-0, -(anything but NaN)) is +-pi ;
+ *      ATAN2(+-(anything but 0 and NaN), 0) is +-pi/2;
+ *      ATAN2(+-(anything but INF and NaN), +INF) is +-0 ;
+ *      ATAN2(+-(anything but INF and NaN), -INF) is +-pi;
+ *      ATAN2(+-INF,+INF ) is +-pi/4 ;
+ *      ATAN2(+-INF,-INF ) is +-3pi/4;
+ *      ATAN2(+-INF, (anything but,0,NaN, and INF)) is +-pi/2;
+ *
+ * Constants:
+ * The hexadecimal values are the intended ones for the following
+ * constants. The decimal values may be used, provided that the
+ * compiler will convert from decimal to binary accurately enough
+ * to produce the hexadecimal values shown.
+ */
+
+#include "libm.h"
+
+static volatile double
+tiny  = 1.0e-300;
+static const double
+zero  = 0.0,
+pi_o_4 = 7.8539816339744827900E-01, /* 0x3FE921FB, 0x54442D18 */
+pi_o_2 = 1.5707963267948965580E+00, /* 0x3FF921FB, 0x54442D18 */
+pi     = 3.1415926535897931160E+00; /* 0x400921FB, 0x54442D18 */
+static volatile double
+pi_lo  = 1.2246467991473531772E-16; /* 0x3CA1A626, 0x33145C07 */
+
+double atan2(double y, double x)
+{
+	double z;
+	int32_t k,m,hx,hy,ix,iy;
+	uint32_t lx,ly;
+
+	EXTRACT_WORDS(hx, lx, x);
+	ix = hx & 0x7fffffff;
+	EXTRACT_WORDS(hy, ly, y);
+	iy = hy & 0x7fffffff;
+	if ((ix|((lx|-lx)>>31)) > 0x7ff00000 ||
+	    (iy|((ly|-ly)>>31)) > 0x7ff00000)  /* x or y is NaN */
+		return x+y;
+	if ((hx-0x3ff00000 | lx) == 0)  /* x = 1.0 */
+		return atan(y);
+	m = ((hy>>31)&1) | ((hx>>30)&2);  /* 2*sign(x)+sign(y) */
+
+	/* when y = 0 */
+	if ((iy|ly) == 0) {
+		switch(m) {
+		case 0:
+		case 1: return y;        /* atan(+-0,+anything)=+-0 */
+		case 2: return  pi+tiny; /* atan(+0,-anything) = pi */
+		case 3: return -pi-tiny; /* atan(-0,-anything) =-pi */
+		}
+	}
+	/* when x = 0 */
+	if ((ix|lx) == 0)
+		return hy < 0 ? -pi_o_2-tiny : pi_o_2+tiny;
+	/* when x is INF */
+	if (ix == 0x7ff00000) {
+		if (iy == 0x7ff00000) {
+			switch(m) {
+			case 0: return  pi_o_4+tiny; /* atan(+INF,+INF) */
+			case 1: return -pi_o_4-tiny; /* atan(-INF,+INF) */
+			case 2: return  3.0*pi_o_4+tiny; /* atan(+INF,-INF) */
+			case 3: return -3.0*pi_o_4-tiny; /* atan(-INF,-INF) */
+			}
+		} else {
+			switch(m) {
+			case 0: return  zero;    /* atan(+...,+INF) */
+			case 1: return -zero;    /* atan(-...,+INF) */
+			case 2: return  pi+tiny; /* atan(+...,-INF) */
+			case 3: return -pi-tiny; /* atan(-...,-INF) */
+			}
+		}
+	}
+	/* when y is INF */
+	if (iy == 0x7ff00000)
+		return hy < 0 ? -pi_o_2-tiny : pi_o_2+tiny;
+
+	/* compute y/x */
+	k = (iy-ix)>>20;
+	if (k > 60) {                  /* |y/x| >  2**60 */
+		z = pi_o_2+0.5*pi_lo;
+		m &= 1;
+	} else if (hx < 0 && k < -60)  /* 0 > |y|/x > -2**-60 */
+		z = 0.0;
+	else                           /* safe to do y/x */
+		z = atan(fabs(y/x));
+	switch (m) {
+	case 0: return z;              /* atan(+,+) */
+	case 1: return -z;             /* atan(-,+) */
+	case 2: return pi - (z-pi_lo); /* atan(+,-) */
+	default: /* case 3 */
+		return (z-pi_lo) - pi; /* atan(-,-) */
+	}
+}