ibm2ieee.m

基于Matlab的地震数据处理显示和测井数据显示于处理的小程序

function d = ibm2ieee (ibmf)

% Name:         ibm2ieee
% Abstract:     convert a matrix of IBM/360 32-bit floats
%               to IEEE doubles.
%
%               IBMF is the matrix of IBM/360 32-bit floats each
%               stored as a 32 bit unsigned big-endian integer
%               in a MATLAB double.
%
%               The format of a IBM/360 32-bit float is:
%
%                  sign 7-bit exponent  24 bit fraction
%                  The base is 16. The decimal point is to
%                  the left of the fraction. The exponent is
%                  biased by +64.
%
%               The basic idea is that you use floating point on
%               the various fields.
%
%               ieee = sign * 16 ^ (exponent - 64) * fraction / 16 ^ 6
%
% By:           Martin Knapp-Cordes
%               The MathWorks, Inc.
%
% Date(s):      Jun 95 - 28, 29

% $Revision: 1.2 $  $Date: 1995/06/29 14:50:03 $
% This M-file is not officially supported by The MathWorks, Inc.  Please use
% it as is, or modify it to your specific need
%
%Assuming you have a file, which contains IBM float 32 format binary data, called
%5702.seg, then you must use the following FOPEN and FREAD call the read the
%file:
%
%   fid = fopen('5702.seg','r','b');
%
%%
%% Read first data record - IBM/360 32-bit floating format
%%                          Read them as unsigned (32-bit) integers.
%% Convert to IEEE doubles using ibm2ieee.
%%
%% size - number of elements to read
%
%    ibm1 = fread(fid,size,'uint');
%    ieee1 = ibm2ieee(ibm1);
%----------------------------------------------------------------------------
%
    if (nargin ~= 1)
        error ('Wrong number of arguments.');
    elseif (isempty(ibmf))
        error ('Argument is an empty matrix');
    end
%
    aibmf = sprintf('%08x',ibmf);
%
% hexd(1) - 1st hex digit - first bit is sign, next 3 bits high order exponent
% hexd(2) - 2nd hex digit - bits of low order exponent
% hexd(3) - 3rd-8th hex digit - bits of fraction
%
    hexd = sscanf(aibmf,'%1x%1x%6x',[3,inf]);
    d = (1 - (hexd(1,:) >= 8) .* 2) .* ...
        16 .^ ((hexd(1,:) - (hexd(1,:) >= 8) .* 8) .* 16 + hexd(2,:) ...
        - 70).* hexd(3,:);
    d = reshape(d,size(ibmf));