| // 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 |
| |
| export log, log10 |
| |
| /* |
| * log returns the natural logarithm of its floating |
| * point argument. |
| * |
| * The coefficients are #2705 from Hart & Cheney. (19.38D) |
| * |
| * It calls frexp. |
| */ |
| |
| const |
| ( |
| log2 = .693147180559945309e0; |
| ln10o1 = .4342944819032518276511; |
| sqrto2 = .707106781186547524e0; |
| p0 = -.240139179559210510e2; |
| p1 = .309572928215376501e2; |
| p2 = -.963769093377840513e1; |
| p3 = .421087371217979714e0; |
| q0 = -.120069589779605255e2; |
| q1 = .194809660700889731e2; |
| q2 = -.891110902798312337e1; |
| ) |
| |
| func |
| log(arg float64) float64 |
| { |
| var x, z, zsq, temp float64; |
| var exp int; |
| |
| if arg <= 0 { |
| return sys.NaN(); |
| } |
| |
| x,exp = sys.frexp(arg); |
| for x < 0.5 { |
| x = x*2; |
| exp = exp-1; |
| } |
| if x < sqrto2 { |
| x = x*2; |
| exp = exp-1; |
| } |
| |
| z = (x-1) / (x+1); |
| zsq = z*z; |
| |
| temp = ((p3*zsq + p2)*zsq + p1)*zsq + p0; |
| temp = temp/(((zsq + q2)*zsq + q1)*zsq + q0); |
| temp = temp*z + float64(exp)*log2; |
| return temp; |
| } |
| |
| func |
| log10(arg float64) float64 |
| { |
| |
| if arg <= 0 { |
| return sys.NaN(); |
| } |
| return log(arg) * ln10o1; |
| } |