Compress Int : int « Data Types « C# / C Sharp
Compress Int
/*
* PERWAPI - An API for Reading and Writing PE Files
*
* Copyright (c) Diane Corney, Queensland University of Technology, 2004.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the PERWAPI Copyright as included with this
* distribution in the file PERWAPIcopyright.rtf.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY as is explained in the copyright notice.
*
* The author may be contacted at d.corney@qut.edu.au
*
* Version Date: 26/01/07
*/
using System;
namespace QUT.PERWAPI
{
/// <summary>
/// Diagnostic
/// </summary>
public class Diag
{
/// <summary>
/// Flag for diagnostic output.
/// </summary>
public static bool DiagOn = false;
}
public static class BlobUtil
{
public static byte[] CompressInt(int val)
{
// This code is based on a revised version of the
// ECMA-335 spec which clarifies the encoding of
// array lower bounds. (kjg 2008-Feb-22 )
//
uint uVal = ((uint)val) << 1;
uint sign = (val < 0 ? (uint)1 : 0);
if (-64 <= val && val <= 63)
{
uVal = uVal & 0x7f | sign;
return new byte[] { (byte)uVal };
}
else if (-8192 <= val && val <= 8191)
{
uVal = uVal & 0x3fff | 0x8000 | sign;
return new byte[] { (byte)(uVal >> 8), (byte)uVal };
}
else if (-268435456 <= val && val <= 268435455)
{
uVal = uVal & 0x1fffffff | 0xc0000000 | sign;
return new byte[] {
(byte)(uVal >> 24),
(byte)(uVal >> 16),
(byte)(uVal >> 8),
(byte)uVal };
}
else
throw new OverflowException("Value cannot be compressed");
}
public static byte[] CompressUInt(uint val)
{
if (val > 0x1fffffff)
throw new OverflowException("Value cannot be compressed");
return CompressNum(val);
}
private static byte[] CompressNum(uint num)
{
byte[] rslt = null;
if (num <= 0x7f)
{
rslt = new byte[1];
rslt[0] = (byte)num;
}
else if (num <= 0x3fff)
{
rslt = new byte[2];
rslt[0] = (byte)((num >> 8) | 0x80);
rslt[1] = (byte)(num & 0xff);
}
else
{
rslt = new byte[4];
rslt[0] = (byte)((num >> 24) | 0xc0);
rslt[1] = (byte)((num >> 16) & 0xff);
rslt[2] = (byte)((num >> 8) & 0xff);
rslt[3] = (byte)(num & 0xff);
}
return rslt;
}
}
}
