Mercurial > octave-nkf
view scripts/specfun/log2.m @ 7522:8a6965a01176
log2: ensure F strictly less than 1
author | John W. Eaton <jwe@octave.org> |
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date | Sun, 24 Feb 2008 03:32:49 -0500 |
parents | 8b7b4f58199f |
children |
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## Copyright (C) 1995, 1996, 1999, 2000, 2002, 2004, 2005, 2006, 2007 ## Kurt Hornik ## ## This file is part of Octave. ## ## Octave is free software; you can redistribute it and/or modify it ## under the terms of the GNU General Public License as published by ## the Free Software Foundation; either version 3 of the License, or (at ## your option) any later version. ## ## Octave is distributed in the hope that it will be useful, but ## WITHOUT ANY WARRANTY; without even the implied warranty of ## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU ## General Public License for more details. ## ## You should have received a copy of the GNU General Public License ## along with Octave; see the file COPYING. If not, see ## <http://www.gnu.org/licenses/>. ## -*- texinfo -*- ## @deftypefn {Mapping Function} {} log2 (@var{x}) ## @deftypefnx {Mapping Function} {[@var{f}, @var{e}] =} log2 (@var{x}) ## Compute the base-2 logarithm of @var{x}. With two outputs, returns ## @var{f} and @var{e} such that ## @iftex ## @tex ## $1/2 <= |f| < 1$ and $x = f \cdot 2^e$. ## @end tex ## @end iftex ## @ifinfo ## 1/2 <= abs(f) < 1 and x = f * 2^e. ## @end ifinfo ## @seealso{log, log10, logspace, exp} ## @end deftypefn ## Author: AW <Andreas.Weingessel@ci.tuwien.ac.at> ## Created: 17 October 1994 ## Adapted-By: jwe function [f, e] = log2 (x) if (nargin != 1) print_usage (); endif if (nargout < 2) f = log (x) / log (2); elseif (nargout == 2) ## Only deal with the real parts ... x = real (x); ## Since log (0) gives problems, 0 entries are replaced by 1. ## This is corrected later by multiplication with the sign. f = abs (x) + (x == 0); e = (floor (log (f) / log (2)) + 1) .* (x != 0); f = sign (x) .* f ./ (2 .^ e); ## Workaround to cases of f == 1 (due to precision issues). idx = abs (f) >= 1; if (any (idx)) f(idx) /= 2; e(idx)++; endif else error ("log2 takes at most 2 output arguments"); endif endfunction %!assert(all (abs (log2 ([1/4, 1/2, 1, 2, 4]) - [-2, -1, 0, 1, 2]) < sqrt (eps))); %!error log2 (); %!error log2 (1, 2);