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diff --git a/src/pkg/math/log.go b/src/pkg/math/log.go
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+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package math
+
+import "math"
+
+// The original C code, the long comment, and the constants
+// below are from FreeBSD's /usr/src/lib/msun/src/e_log.c
+// and came with this notice.  The go code is a simpler
+// version of the original 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.
+// ====================================================
+//
+// __ieee754_log(x)
+// Return the logrithm of x
+//
+// Method :
+//   1. Argument Reduction: find k and f such that
+//			x = 2^k * (1+f),
+//	   where  sqrt(2)/2 < 1+f < sqrt(2) .
+//
+//   2. Approximation of log(1+f).
+//	Let s = f/(2+f) ; based on log(1+f) = log(1+s) - log(1-s)
+//		 = 2s + 2/3 s**3 + 2/5 s**5 + .....,
+//	     	 = 2s + s*R
+//      We use a special Reme algorithm on [0,0.1716] to generate
+// 	a polynomial of degree 14 to approximate R The maximum error
+//	of this polynomial approximation is bounded by 2**-58.45. In
+//	other words,
+//		        2      4      6      8      10      12      14
+//	    R(z) ~ L1*s +L2*s +L3*s +L4*s +L5*s  +L6*s  +L7*s
+//  	(the values of L1 to L7 are listed in the program)
+//	and
+//	    |      2          14          |     -58.45
+//	    | L1*s +...+L7*s    -  R(z) | <= 2
+//	    |                             |
+//	Note that 2s = f - s*f = f - hfsq + s*hfsq, where hfsq = f*f/2.
+//	In order to guarantee error in log below 1ulp, we compute log
+//	by
+//		log(1+f) = f - s*(f - R)	(if f is not too large)
+//		log(1+f) = f - (hfsq - s*(hfsq+R)).	(better accuracy)
+//
+//	3. Finally,  log(x) = k*Ln2 + log(1+f).
+//			    = k*Ln2_hi+(f-(hfsq-(s*(hfsq+R)+k*Ln2_lo)))
+//	   Here Ln2 is split into two floating point number:
+//			Ln2_hi + Ln2_lo,
+//	   where n*Ln2_hi is always exact for |n| < 2000.
+//
+// Special cases:
+//	log(x) is NaN with signal if x < 0 (including -INF) ;
+//	log(+INF) is +INF; log(0) is -INF with signal;
+//	log(NaN) is that NaN with no signal.
+//
+// Accuracy:
+//	according to an error analysis, the error is always less than
+//	1 ulp (unit in the last place).
+//
+// 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.
+
+// Log returns the natural logarithm of x.
+//
+// Special cases are:
+//	Log(+Inf) = +Inf
+//	Log(0) = -Inf
+//	Log(x < 0) = NaN
+//	Log(NaN) = NaN
+func Log(x float64) float64 {
+	const (
+		Ln2Hi = 6.93147180369123816490e-01;	/* 3fe62e42 fee00000 */
+		Ln2Lo = 1.90821492927058770002e-10;	/* 3dea39ef 35793c76 */
+		L1 = 6.666666666666735130e-01;  /* 3FE55555 55555593 */
+		L2 = 3.999999999940941908e-01;  /* 3FD99999 9997FA04 */
+		L3 = 2.857142874366239149e-01;  /* 3FD24924 94229359 */
+		L4 = 2.222219843214978396e-01;  /* 3FCC71C5 1D8E78AF */
+		L5 = 1.818357216161805012e-01;  /* 3FC74664 96CB03DE */
+		L6 = 1.531383769920937332e-01;  /* 3FC39A09 D078C69F */
+		L7 = 1.479819860511658591e-01;  /* 3FC2F112 DF3E5244 */
+	)
+
+	// special cases
+	switch {
+	case IsNaN(x) || IsInf(x, 1):
+		return x;
+	case x < 0:
+		return NaN();
+	case x == 0:
+		return Inf(-1);
+	}
+
+	// reduce
+	f1, ki := Frexp(x);
+	if f1 < Sqrt2/2 {
+		f1 *= 2;
+		ki--;
+	}
+	f := f1 - 1;
+	k := float64(ki);
+
+	// compute
+	s := f/(2+f);
+	s2 := s*s;
+	s4 := s2*s2;
+	t1 := s2*(L1 + s4*(L3 + s4*(L5 + s4*L7)));
+	t2 := s4*(L2 + s4*(L4 + s4*L6));
+	R :=  t1 + t2;
+	hfsq := 0.5*f*f;
+	return k*Ln2Hi - ((hfsq-(s*(hfsq+R)+k*Ln2Lo)) - f);
+}
+
+// Log10 returns the decimal logarthm of x.
+// The special cases are the same as for Log.
+func Log10(x float64) float64 {
+	if x <= 0 {
+		return NaN();
+	}
+	return Log(x) * (1/Ln10);
+}
+