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

fusl/src/math/expf.c

+/* origin: FreeBSD /usr/src/lib/msun/src/e_expf.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
+half[2] = {0.5,-0.5},
+ln2hi   = 6.9314575195e-1f,  /* 0x3f317200 */
+ln2lo   = 1.4286067653e-6f,  /* 0x35bfbe8e */
+invln2  = 1.4426950216e+0f,  /* 0x3fb8aa3b */
+/*
+ * Domain [-0.34568, 0.34568], range ~[-4.278e-9, 4.447e-9]:
+ * |x*(exp(x)+1)/(exp(x)-1) - p(x)| < 2**-27.74
+ */
+P1 =  1.6666625440e-1f, /*  0xaaaa8f.0p-26 */
+P2 = -2.7667332906e-3f; /* -0xb55215.0p-32 */
+
+float expf(float x)
+{
+        float_t hi, lo, c, xx, y;
+        int k, sign;
+        uint32_t hx;
+
+        GET_FLOAT_WORD(hx, x);
+        sign = hx >> 31;   /* sign bit of x */
+        hx &= 0x7fffffff;  /* high word of |x| */
+
+        /* special cases */
+        if (hx >= 0x42aeac50) {  /* if |x| >= -87.33655f or NaN */
+                if (hx >= 0x42b17218 && !sign) {  /* x >= 88.722839f */
+                        /* overflow */
+                        x *= 0x1p127f;
+                        return x;
+                }
+                if (sign) {
+                        /* underflow */
+                        FORCE_EVAL(-0x1p-149f/x);
+                        if (hx >= 0x42cff1b5)  /* x <= -103.972084f */
+                                return 0;
+                }
+        }
+
+        /* argument reduction */
+        if (hx > 0x3eb17218) {  /* if |x| > 0.5 ln2 */
+                if (hx > 0x3f851592)  /* if |x| > 1.5 ln2 */
+                        k = invln2*x + half[sign];
+                else
+                        k = 1 - sign - sign;
+                hi = x - k*ln2hi;  /* k*ln2hi is exact here */
+                lo = k*ln2lo;
+                x = hi - lo;
+        } else if (hx > 0x39000000) {  /* |x| > 2**-14 */
+                k = 0;
+                hi = x;
+                lo = 0;
+        } else {
+                /* raise inexact */
+                FORCE_EVAL(0x1p127f + x);
+                return 1 + x;
+        }
+
+        /* x is now in primary range */
+        xx = x*x;
+        c = x - xx*(P1+xx*P2);
+        y = 1 + (x*c/(2-c) - lo + hi);
+        if (k == 0)
+                return y;
+        return scalbnf(y, k);
+}