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.

src/math/sqrtf.c

@@ -0,0 +1,84 @@
+/* origin: FreeBSD /usr/src/lib/msun/src/e_sqrtf.c */
+/*
+ * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
+ */
+/*
+ * ====================================================
+ * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
+ *
+ * Developed at SunPro, a Sun Microsystems, Inc. business.
+ * Permission to use, copy, modify, and distribute this
+ * software is freely granted, provided that this notice
+ * is preserved.
+ * ====================================================
+ */
+
+#include "libm.h"
+
+static const float one = 1.0, tiny = 1.0e-30;
+
+float sqrtf(float x)
+{
+	float z;
+	int32_t sign = (int)0x80000000;
+	int32_t ix,s,q,m,t,i;
+	uint32_t r;
+
+	GET_FLOAT_WORD(ix, x);
+
+	/* take care of Inf and NaN */
+	if ((ix&0x7f800000) == 0x7f800000)
+		return x*x + x; /* sqrt(NaN)=NaN, sqrt(+inf)=+inf, sqrt(-inf)=sNaN */
+
+	/* take care of zero */
+	if (ix <= 0) {
+		if ((ix&~sign) == 0)
+			return x;  /* sqrt(+-0) = +-0 */
+		if (ix < 0)
+			return (x-x)/(x-x);  /* sqrt(-ve) = sNaN */
+	}
+	/* normalize x */
+	m = ix>>23;
+	if (m == 0) {  /* subnormal x */
+		for (i = 0; (ix&0x00800000) == 0; i++)
+			ix<<=1;
+		m -= i - 1;
+	}
+	m -= 127;  /* unbias exponent */
+	ix = (ix&0x007fffff)|0x00800000;
+	if (m&1)  /* odd m, double x to make it even */
+		ix += ix;
+	m >>= 1;  /* m = [m/2] */
+
+	/* generate sqrt(x) bit by bit */
+	ix += ix;
+	q = s = 0;       /* q = sqrt(x) */
+	r = 0x01000000;  /* r = moving bit from right to left */
+
+	while (r != 0) {
+		t = s + r;
+		if (t <= ix) {
+			s = t+r;
+			ix -= t;
+			q += r;
+		}
+		ix += ix;
+		r >>= 1;
+	}
+
+	/* use floating add to find out rounding direction */
+	if (ix != 0) {
+		z = one - tiny; /* raise inexact flag */
+		if (z >= one) {
+			z = one + tiny;
+			if (z > one)
+				q += 2;
+			else
+				q += q & 1;
+		}
+	}
+	ix = (q>>1) + 0x3f000000;
+	ix += m << 23;
+	SET_FLOAT_WORD(z, ix);
+	return z;
+}