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

fusl/src/math/expm1f.c

+/* origin: FreeBSD /usr/src/lib/msun/src/s_expm1f.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
+o_threshold = 8.8721679688e+01, /* 0x42b17180 */
+ln2_hi      = 6.9313812256e-01, /* 0x3f317180 */
+ln2_lo      = 9.0580006145e-06, /* 0x3717f7d1 */
+invln2      = 1.4426950216e+00, /* 0x3fb8aa3b */
+/*
+ * Domain [-0.34568, 0.34568], range ~[-6.694e-10, 6.696e-10]:
+ * |6 / x * (1 + 2 * (1 / (exp(x) - 1) - 1 / x)) - q(x)| < 2**-30.04
+ * Scaled coefficients: Qn_here = 2**n * Qn_for_q (see s_expm1.c):
+ */
+Q1 = -3.3333212137e-2, /* -0x888868.0p-28 */
+Q2 =  1.5807170421e-3; /*  0xcf3010.0p-33 */
+
+float expm1f(float x)
+{
+        float_t y,hi,lo,c,t,e,hxs,hfx,r1,twopk;
+        union {float f; uint32_t i;} u = {x};
+        uint32_t hx = u.i & 0x7fffffff;
+        int k, sign = u.i >> 31;
+
+        /* filter out huge and non-finite argument */
+        if (hx >= 0x4195b844) {  /* if |x|>=27*ln2 */
+                if (hx > 0x7f800000)  /* NaN */
+                        return x;
+                if (sign)
+                        return -1;
+                if (x > o_threshold) {
+                        x *= 0x1p127f;
+                        return x;
+                }
+        }
+
+        /* argument reduction */
+        if (hx > 0x3eb17218) {           /* if  |x| > 0.5 ln2 */
+                if (hx < 0x3F851592) {       /* and |x| < 1.5 ln2 */
+                        if (!sign) {
+                                hi = x - ln2_hi;
+                                lo = ln2_lo;
+                                k =  1;
+                        } else {
+                                hi = x + ln2_hi;
+                                lo = -ln2_lo;
+                                k = -1;
+                        }
+                } else {
+                        k  = invln2*x + (sign ? -0.5f : 0.5f);
+                        t  = k;
+                        hi = x - t*ln2_hi;      /* t*ln2_hi is exact here */
+                        lo = t*ln2_lo;
+                }
+                x = hi-lo;
+                c = (hi-x)-lo;
+        } else if (hx < 0x33000000) {  /* when |x|<2**-25, return x */
+                if (hx < 0x00800000)
+                        FORCE_EVAL(x*x);
+                return x;
+        } else
+                k = 0;
+
+        /* x is now in primary range */
+        hfx = 0.5f*x;
+        hxs = x*hfx;
+        r1 = 1.0f+hxs*(Q1+hxs*Q2);
+        t  = 3.0f - r1*hfx;
+        e  = hxs*((r1-t)/(6.0f - x*t));
+        if (k == 0)  /* c is 0 */
+                return x - (x*e-hxs);
+        e  = x*(e-c) - c;
+        e -= hxs;
+        /* exp(x) ~ 2^k (x_reduced - e + 1) */
+        if (k == -1)
+                return 0.5f*(x-e) - 0.5f;
+        if (k == 1) {
+                if (x < -0.25f)
+                        return -2.0f*(e-(x+0.5f));
+                return 1.0f + 2.0f*(x-e);
+        }
+        u.i = (0x7f+k)<<23;  /* 2^k */
+        twopk = u.f;
+        if (k < 0 || k > 56) {   /* suffice to return exp(x)-1 */
+                y = x - e + 1.0f;
+                if (k == 128)
+                        y = y*2.0f*0x1p127f;
+                else
+                        y = y*twopk;
+                return y - 1.0f;
+        }
+        u.i = (0x7f-k)<<23;  /* 2^-k */
+        if (k < 23)
+                y = (x-e+(1-u.f))*twopk;
+        else
+                y = (x-(e+u.f)+1)*twopk;
+        return y;
+}