1 files changed, 112 insertions, 0 deletions
diff --git a/lib/libm/expm1f.c b/lib/libm/expm1f.c
new file mode 100644
index 00000000..7cc13b91
--- /dev/null
+++ b/lib/libm/expm1f.c
@@ -0,0 +1,112 @@
+/* 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 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 (hx > 0x42b17217) { /* x > log(FLT_MAX) */
+			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;
+}