From 7ce331c01ce6eb7b3f5c715a38a24359da9c6ee2 Mon Sep 17 00:00:00 2001
From: Eric Andersen <andersen@codepoet.org>
Date: Thu, 22 Nov 2001 14:04:29 +0000
Subject: Totally rework the math library, this time based on the MacOs X math
 library (which is itself based on the math lib from FreeBSD).  -Erik

---
 libm/e_log10.c | 98 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 98 insertions(+)
 create mode 100644 libm/e_log10.c

(limited to 'libm/e_log10.c')

diff --git a/libm/e_log10.c b/libm/e_log10.c
new file mode 100644
index 000000000..5d004ac4e
--- /dev/null
+++ b/libm/e_log10.c
@@ -0,0 +1,98 @@
+/* @(#)e_log10.c 5.1 93/09/24 */
+/*
+ * ====================================================
+ * 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.
+ * ====================================================
+ */
+
+#if defined(LIBM_SCCS) && !defined(lint)
+static char rcsid[] = "$NetBSD: e_log10.c,v 1.9 1995/05/10 20:45:51 jtc Exp $";
+#endif
+
+/* __ieee754_log10(x)
+ * Return the base 10 logarithm of x
+ * 
+ * Method :
+ *	Let log10_2hi = leading 40 bits of log10(2) and
+ *	    log10_2lo = log10(2) - log10_2hi,
+ *	    ivln10   = 1/log(10) rounded.
+ *	Then
+ *		n = ilogb(x), 
+ *		if(n<0)  n = n+1;
+ *		x = scalbn(x,-n);
+ *		log10(x) := n*log10_2hi + (n*log10_2lo + ivln10*log(x))
+ *
+ * Note 1:
+ *	To guarantee log10(10**n)=n, where 10**n is normal, the rounding 
+ *	mode must set to Round-to-Nearest.
+ * Note 2:
+ *	[1/log(10)] rounded to 53 bits has error  .198   ulps;
+ *	log10 is monotonic at all binary break points.
+ *
+ * Special cases:
+ *	log10(x) is NaN with signal if x < 0; 
+ *	log10(+INF) is +INF with no signal; log10(0) is -INF with signal;
+ *	log10(NaN) is that NaN with no signal;
+ *	log10(10**N) = N  for N=0,1,...,22.
+ *
+ * Constants:
+ * The hexadecimal values are the intended ones for the following constants.
+ * The decimal values may be used, provided that the compiler will convert
+ * from decimal to binary accurately enough to produce the hexadecimal values
+ * shown.
+ */
+
+#include "math.h"
+#include "math_private.h"
+
+#ifdef __STDC__
+static const double
+#else
+static double
+#endif
+two54      =  1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */
+ivln10     =  4.34294481903251816668e-01, /* 0x3FDBCB7B, 0x1526E50E */
+log10_2hi  =  3.01029995663611771306e-01, /* 0x3FD34413, 0x509F6000 */
+log10_2lo  =  3.69423907715893078616e-13; /* 0x3D59FEF3, 0x11F12B36 */
+
+#ifdef __STDC__
+static const double zero   =  0.0;
+#else
+static double zero   =  0.0;
+#endif
+
+#ifdef __STDC__
+	double __ieee754_log10(double x)
+#else
+	double __ieee754_log10(x)
+	double x;
+#endif
+{
+	double y,z;
+	int32_t i,k,hx;
+	u_int32_t lx;
+
+	EXTRACT_WORDS(hx,lx,x);
+
+        k=0;
+        if (hx < 0x00100000) {                  /* x < 2**-1022  */
+            if (((hx&0x7fffffff)|lx)==0)
+                return -two54/zero;             /* log(+-0)=-inf */
+            if (hx<0) return (x-x)/zero;        /* log(-#) = NaN */
+            k -= 54; x *= two54; /* subnormal number, scale up x */
+	    GET_HIGH_WORD(hx,x);
+        }
+	if (hx >= 0x7ff00000) return x+x;
+	k += (hx>>20)-1023;
+	i  = ((u_int32_t)k&0x80000000)>>31;
+        hx = (hx&0x000fffff)|((0x3ff-i)<<20);
+        y  = (double)(k+i);
+	SET_HIGH_WORD(x,hx);
+	z  = y*log10_2lo + ivln10*__ieee754_log(x);
+	return  z+y*log10_2hi;
+}
-- 
cgit v1.2.3