1 files changed, 80 insertions, 0 deletions
diff --git a/lib/libm/log1pf.c b/lib/libm/log1pf.c
new file mode 100644
index 00000000..bdd702d1
--- /dev/null
+++ b/lib/libm/log1pf.c
@@ -0,0 +1,80 @@
+/* origin: FreeBSD /usr/src/lib/msun/src/s_log1pf.c */
+/*
+ * ====================================================
+ * 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 */
+	/* |(log(1+s)-log(1-s))/s - Lg(s)| < 2**-34.24 (~[-4.95e-11, 4.97e-11]).
+	 */
+	Lg1 = 0xaaaaaa.0p-24, /* 0.66666662693 */
+	Lg2 = 0xccce13.0p-25, /* 0.40000972152 */
+	Lg3 = 0x91e9ee.0p-25, /* 0.28498786688 */
+	Lg4 = 0xf89e26.0p-26; /* 0.24279078841 */
+
+float log1pf(float x)
+{
+	union {
+		float f;
+		uint32_t i;
+	} u = { x };
+	float_t hfsq, f, c, s, z, R, w, t1, t2, dk;
+	uint32_t ix, iu;
+	int k;
+
+	ix = u.i;
+	k = 1;
+	if (ix < 0x3ed413d0 || ix >> 31) { /* 1+x < sqrt(2)+  */
+		if (ix >= 0xbf800000) {	   /* x <= -1.0 */
+			if (x == -1)
+				return x / 0.0f; /* log1p(-1)=+inf */
+			return (x - x) / 0.0f;	 /* log1p(x<-1)=NaN */
+		}
+		if (ix << 1 < 0x33800000 << 1) { /* |x| < 2**-24 */
+			/* underflow if subnormal */
+			if ((ix & 0x7f800000) == 0)
+				FORCE_EVAL(x * x);
+			return x;
+		}
+		if (ix <= 0xbe95f619) { /* sqrt(2)/2- <= 1+x < sqrt(2)+ */
+			k = 0;
+			c = 0;
+			f = x;
+		}
+	} else if (ix >= 0x7f800000)
+		return x;
+	if (k) {
+		u.f = 1 + x;
+		iu = u.i;
+		iu += 0x3f800000 - 0x3f3504f3;
+		k = (int)(iu >> 23) - 0x7f;
+		/* correction term ~ log(1+x)-log(u), avoid underflow in c/u */
+		if (k < 25) {
+			c = k >= 2 ? 1 - (u.f - x) : x - (u.f - 1);
+			c /= u.f;
+		} else
+			c = 0;
+		/* reduce u into [sqrt(2)/2, sqrt(2)] */
+		iu = (iu & 0x007fffff) + 0x3f3504f3;
+		u.i = iu;
+		f = u.f - 1;
+	}
+	s = f / (2.0f + f);
+	z = s * s;
+	w = z * z;
+	t1 = w * (Lg2 + w * Lg4);
+	t2 = z * (Lg1 + w * Lg3);
+	R = t2 + t1;
+	hfsq = 0.5f * f * f;
+	dk = k;
+	return s * (hfsq + R) + (dk * ln2_lo + c) - hfsq + f + dk * ln2_hi;
+}