X-Git-Url: http://nsz.repo.hu/git/?a=blobdiff_plain;f=src%2Fmath%2Fatanhl.c;h=87cd1cdb5f325f01cf12d19594efbcead93472b1;hb=b36c37f6fa9692b03bbdeda2b57b2e8a26d8f315;hp=931bae32f92e3b2b6afae51dd8f31b862f3ffb61;hpb=0cbb65479147ecdaa664e88cc2a5a925f3de502f;p=musl

diff --git a/src/math/atanhl.c b/src/math/atanhl.c
index 931bae32..87cd1cdb 100644
--- a/src/math/atanhl.c
+++ b/src/math/atanhl.c
@@ -1,31 +1,3 @@
-/* origin: OpenBSD /usr/src/lib/libm/src/ld80/e_atanh.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.
- * ====================================================
- */
-/* atanhl(x)
- * Method :
- *    1.Reduced x to positive by atanh(-x) = -atanh(x)
- *    2.For x>=0.5
- *                   1              2x                          x
- *      atanhl(x) = --- * log(1 + -------) = 0.5 * log1p(2 * --------)
- *                   2             1 - x                      1 - x
- *
- *      For x<0.5
- *      atanhl(x) = 0.5*log1pl(2x+2x*x/(1-x))
- *
- * Special cases:
- *      atanhl(x) is NaN if |x| > 1 with signal;
- *      atanhl(NaN) is that NaN with no signal;
- *      atanhl(+-1) is +-INF with signal.
- */
-
 #include "libm.h"
 
 #if LDBL_MANT_DIG == 53 && LDBL_MAX_EXP == 1024
@@ -33,32 +5,31 @@ long double atanhl(long double x)
 {
 	return atanh(x);
 }
-#elif LDBL_MANT_DIG == 64 && LDBL_MAX_EXP == 16384
-static const long double huge = 1e4900L;
-
+#elif (LDBL_MANT_DIG == 64 || LDBL_MANT_DIG == 113) && LDBL_MAX_EXP == 16384
+/* atanh(x) = log((1+x)/(1-x))/2 = log1p(2x/(1-x))/2 ~= x + x^3/3 + o(x^5) */
 long double atanhl(long double x)
 {
-	long double t;
-	int32_t ix;
-	uint32_t se,i0,i1;
+	union ldshape u = {x};
+	unsigned e = u.i.se & 0x7fff;
+	unsigned s = u.i.se >> 15;
+
+	/* |x| */
+	u.i.se = e;
+	x = u.f;
 
-	GET_LDOUBLE_WORDS(se, i0, i1, x);
-	ix = se & 0x7fff;
-	if ((ix+((((i0&0x7fffffff)|i1)|(-((i0&0x7fffffff)|i1)))>>31)) > 0x3fff)
-		/* |x| > 1 */
-		return (x-x)/(x-x);
-	if (ix == 0x3fff)
-		return x/0.0;
-	if (ix < 0x3fe3 && huge+x > 0.0)  /* x < 2**-28 */
-		return x;
-	SET_LDOUBLE_EXP(x, ix);
-	if (ix < 0x3ffe) {  /* x < 0.5 */
-		t = x + x;
-		t = 0.5*log1pl(t + t*x/(1.0 - x));
-	} else
-		t = 0.5*log1pl((x + x)/(1.0 - x));
-	if (se <= 0x7fff)
-		return t;
-	return -t;
+	if (e < 0x3ff - 1) {
+		if (e < 0x3ff - LDBL_MANT_DIG/2) {
+			/* handle underflow */
+			if (e == 0)
+				FORCE_EVAL((float)x);
+		} else {
+			/* |x| < 0.5, up to 1.7ulp error */
+			x = 0.5*log1pl(2*x + 2*x*x/(1-x));
+		}
+	} else {
+		/* avoid overflow */
+		x = 0.5*log1pl(2*(x/(1-x)));
+	}
+	return s ? -x : x;
 }
 #endif