Question

I need to read files produced by a legacy Windows app that stores real numbers (the 8-byte “double” type) in binary – i.e. as a packed array of 8 bytes. I can read the 8 byte group OK but how can I present it to my ASP JScript code such I can get the real number back again.

Or to put it another way:

Say a file was produced by a Windows (Delphi) program:

Assign (f, 'test.bin') ;
rewrite (f, 1) ;
r := 1234.56E78 ;
BlockWrite (f, r, SizeOf (Double)) ;
Close (f) ;

Inspection of the file will show it contains 8 bytes, being:

94 0E 4C CA C2 97 AD 53

which is the real number in IEEE format. Assuming I can read these 8 bytes back in ASP, is there a simple way of getting the real number back again?

Answer 1

Look at BitConverter.ToDouble().

In an ASP.NET page, this could look like:

<%@ Page Language="JScript"
    AutoEventWireup="true"
    CodeBehind="Default.aspx.cs"
    Inherits="WebApplication1._Default" %>
<%
    var bytes: byte[] = [0x94, 0x0e, 0x4c, 0xca, 0xc2, 0x97, 0xad, 0x53];
    var d = BitConverter.ToDouble(bytes, 0);
    Response.Write(d);
%>

Which gets you the output:

1.2345678E+95

(You can check for correctness at http://babbage.cs.qc.edu/IEEE-754/)