AWARE SYSTEMS
TIFF and LibTiff Mail List Archive

Thread

1994.09.16 04:17 "TIFF Bit Ordering Versus Fill Order", by John M Davison
[...]
1994.09.19 22:46 "Re: Now that you mention bit order...", by Sam Leffler
1994.09.19 23:53 "RE: Now that you mention bit order...", by Craig Jackson
[...]

1994.09.19 23:53 "RE: Now that you mention bit order...", by Craig Jackson

Let me state my problem:

I'm working on a little-ending machine (a VAX running VMS). I've got a scaling algorithm that wants me to march through each scanline bit-by-bit. My present algorithm does it one byte at a time, by using a mask which rotates from 0x80 to 0x01.

Now if I were on a big-endian machine, with MSB bit order, I could do things 4 bytes at a time, by having my mask rotate from 0x80000000 to 0x00000001. But if I am on a little-endian machine, with the data being returned in MSB order, my mask sequence to accomplish the same thing would be 0x00000080.. 0x00000001,0x00008000.. 0x00000100, 0x00800000.. 0x00010000, 0x80000000.. 0x01000000.

If I could set LSB order as the working order of the library, I could just rotate my mask uniformly from 0x00000001 to 0x80000000.

Maybe I don't know some trick that all good image-processors should know, but it seems to me that using LSB order on a little-endian machine would be easier for this algorithm.

Craig Jackson
craigj@epub.ziff.com
Electronic Publishing,
Information Access Company