Add a "fork" of musl as //fusl.

fusl/src/math/atanf.c

+/* origin: FreeBSD /usr/src/lib/msun/src/s_atanf.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 atanhi[] = {
+  4.6364760399e-01, /* atan(0.5)hi 0x3eed6338 */
+  7.8539812565e-01, /* atan(1.0)hi 0x3f490fda */
+  9.8279368877e-01, /* atan(1.5)hi 0x3f7b985e */
+  1.5707962513e+00, /* atan(inf)hi 0x3fc90fda */
+};
+
+static const float atanlo[] = {
+  5.0121582440e-09, /* atan(0.5)lo 0x31ac3769 */
+  3.7748947079e-08, /* atan(1.0)lo 0x33222168 */
+  3.4473217170e-08, /* atan(1.5)lo 0x33140fb4 */
+  7.5497894159e-08, /* atan(inf)lo 0x33a22168 */
+};
+
+static const float aT[] = {
+  3.3333328366e-01,
+ -1.9999158382e-01,
+  1.4253635705e-01,
+ -1.0648017377e-01,
+  6.1687607318e-02,
+};
+
+float atanf(float x)
+{
+        float_t w,s1,s2,z;
+        uint32_t ix,sign;
+        int id;
+
+        GET_FLOAT_WORD(ix, x);
+        sign = ix>>31;
+        ix &= 0x7fffffff;
+        if (ix >= 0x4c800000) {  /* if |x| >= 2**26 */
+                if (isnan(x))
+                        return x;
+                z = atanhi[3] + 0x1p-120f;
+                return sign ? -z : z;
+        }
+        if (ix < 0x3ee00000) {   /* |x| < 0.4375 */
+                if (ix < 0x39800000) {  /* |x| < 2**-12 */
+                        if (ix < 0x00800000)
+                                /* raise underflow for subnormal x */
+                                FORCE_EVAL(x*x);
+                        return x;
+                }
+                id = -1;
+        } else {
+                x = fabsf(x);
+                if (ix < 0x3f980000) {  /* |x| < 1.1875 */
+                        if (ix < 0x3f300000) {  /*  7/16 <= |x| < 11/16 */
+                                id = 0;
+                                x = (2.0f*x - 1.0f)/(2.0f + x);
+                        } else {                /* 11/16 <= |x| < 19/16 */
+                                id = 1;
+                                x = (x - 1.0f)/(x + 1.0f);
+                        }
+                } else {
+                        if (ix < 0x401c0000) {  /* |x| < 2.4375 */
+                                id = 2;
+                                x = (x - 1.5f)/(1.0f + 1.5f*x);
+                        } else {                /* 2.4375 <= |x| < 2**26 */
+                                id = 3;
+                                x = -1.0f/x;
+                        }
+                }
+        }
+        /* end of argument reduction */
+        z = x*x;
+        w = z*z;
+        /* break sum from i=0 to 10 aT[i]z**(i+1) into odd and even poly */
+        s1 = z*(aT[0]+w*(aT[2]+w*aT[4]));
+        s2 = w*(aT[1]+w*aT[3]);
+        if (id < 0)
+                return x - x*(s1+s2);
+        z = atanhi[id] - ((x*(s1+s2) - atanlo[id]) - x);
+        return sign ? -z : z;
+}