I'm attempting to mimic the function used for creating CRC's in PNG files, I'm using the autodin II polynomial and the source code from:
http://www.opensource.apple.com/source/xnu/xnu-1456.1.26/bsd/libkern/crc32.c

My tests have all been for the IHDR chunk, so my parameters have been:
crc - 0xffffffff and 0 (both have been suggested)
buff - the address of the IHDR Chunk's type.
length - the IHDR Chunk's length + 4 (the length of the chunk's data + the length of the type)

I printed the calculated CRC in binary, which I compared to the actual CRC of the chunk. I can see no similarities (little-big endian, reversed bits, XOR'd, etc).

This is the data for the IHDR chunk (hexadecimal format):
length(big endian): d0 00 00 00 (13)
type: 49 48 44 52
data: 00 00 01 77 00 00 01 68 08 06 00 00 00 existing CRC: b0 bb 40 ac

If anyone can tell me why my calculations are off, or give me a CRC32 function that will work I would greatly appreciate it. Thank-you!