www.pudn.com > voicebox2.zip > BITSPREC.M

function y=bitsprec(x,n,mode) 
%BITSPREC round values to a specified fixed or floating precision (X,N,MODE) 
% 
% mode is of the form 'uvw' where: 
%     u: s - n significant bits (default)  
%        f - fixed point: n bits after binary point 
%     v: n - round to nearest (default) 
%        p - round towards +infinity 
%        m - round towards -infinity 
%        z - round towards zero 
% w is only needed if v=n in which case it dictates what to 
%        do if x is min-way between two rounded values: 
%     w: p,m - as above 
%        e - round to nearest even number (default) 
%        o - round to nearest odd number 
%        a - round away from zero 
% mode='*ne' and '*no' are convergent rounding and introduce 
% no DC offset into the result so long as even and odd integer parts are 
% equally common. 
% 
% Examples of y=bitsprec(x,0,'***'): 
% 
%      x    fp-  fm-  fz-  fne  fno  fnp  fnm  fna  
%    
%     2.5    3    2    2    2    3    3    2    3 
%     1.5    2    1    1    2    1    2    1    2 
%     1.1    2    1    1    1    1    1    1    1 
%     1.0    1    1    1    1    1    1    1    1 
%     0.9    1    0    0    1    1    1    1    1 
%     0.5    1    0    0    0    1    1    0    1 
%     0.1    1    0    0    0    0    0    0    0 
%    -0.1    0   -1    0    0    0    0    0    0 
%    -0.5    0   -1    0    0   -1    0   -1   -1 
%    -0.9    0   -1    0   -1   -1   -1   -1   -1 
%    -1.5   -1   -2   -1   -2   -1   -1   -2   -2 
 
%      Copyright (C) Mike Brookes 1997 
% 
%      Last modified Mon Jun  4 08:18:22 2001 
% 
%   VOICEBOX is a MATLAB toolbox for speech processing. Home page is at 
%   http://www.ee.ic.ac.uk/hp/staff/dmb/voicebox/voicebox.html 
% 
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
%   This program 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 2 of the License, or 
%   (at your option) any later version. 
% 
%   This program 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 can obtain a copy of the GNU General Public License from 
%   ftp://prep.ai.mit.edu/pub/gnu/COPYING-2.0 or by writing to 
%   Free Software Foundation, Inc.,675 Mass Ave, Cambridge, MA 02139, USA. 
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
 
if nargin<3 
   mode='sne'; 
end 
if mode(1)=='f' 
   e=0; 
else 
   [x,e]=log2(x); 
end 
switch mode(2) 
case 'p' 
   y=pow2(ceil(pow2(x,n)),e-n); 
case 'm' 
   y=pow2(floor(pow2(x,n)),e-n); 
case 'z' 
   y=pow2(fix(pow2(x,n)),e-n); 
otherwise 
   switch mode(3) 
   case 'a' 
      y=pow2(round(pow2(x,n)),e-n); 
   case 'p' 
      y=pow2(floor(pow2(x,n)+0.5),e-n); 
   case 'm' 
      y=pow2(ceil(pow2(x,n)-0.5),e-n); 
   otherwise 
      z=pow2(x,n-1); 
      switch mode(3) 
      case 'e' 
         y=pow2(floor(pow2(x,n)+0.5)-floor(z+0.75)+ceil(z-0.25),e-n); 
      case 'o' 
         y=pow2(ceil(pow2(x,n)-0.5)+floor(z+0.75)-ceil(z-0.25),e-n); 
      end       
   end 
end