C# Unsafe Bug
- From: "JS" <stonge-jim@xxxxxx>
- Date: 31 Dec 2005 02:30:04 -0800
I was writing some routines which could do bitwise boolean operations
on byte arrays, and I ran into what I think is a bug with C#'s unsafe
code. I am pasting a console application below. Can anyone give an
explanation, or has this type of problem been reported already?
Thanks.
using System;
using System.Collections.Generic;
using System.Text;
namespace UnsafeBug
{
class Program
{
static void Main(string[] args)
{
byte[] dest = new byte[] { 0x01, 0xff };
byte[] sdata1 = new byte[] { 0x01, 0xff };
UnsafeOr(sdata1, dest, dest, 7);
for (int ii = 0; ii < dest.Length; ii++)
{
Console.WriteLine("Byte {0} = 0x{1:X2}", ii + 1, dest[ii]);
}
Console.WriteLine("Hit Enter to quit..."); Console.ReadLine();
}
// OR's together 2 byte arrays into 'dest' without touching the
first few bits of 'dest'.
// it is allowed for sources/destinations to be the same.
static void UnsafeOr(byte[] src1, byte[] src2, byte[] dest, int
firstBit)
{
byte mask = (byte)(0x80 >> firstBit);
int nbytes = Math.Min(Math.Min(src1.Length, src2.Length),
dest.Length);
unsafe
{
fixed (byte* s1data = &src1[0], s2data = &src2[0], ddata =
&dest[0])
{
byte* s1ptr = s1data;
byte* s2ptr = s2data;
byte* dptr = ddata;
#if false
// this version works
byte val = (byte)(*dptr & ~mask);
*dptr++ = (byte)(val | ((*s1ptr++ | *s2ptr++)&mask));
#else
// this version does not work
*dptr++ = (byte)((*dptr & ~mask) | ((*s1ptr++ |
*s2ptr++)&mask));
#endif
for (int ii = 1; ii < nbytes; ii++)
{
*dptr++ = (byte)(*s1ptr++ | *s2ptr++);
}
}
}
}
}
}
.
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