On 02/17/2011 06:40 AM, Will Woods wrote: > The most significant reason we might want to use xz instead of lzma is > integrity checking - gzip and xz use crc32, lzma has none. That's not really true. If the header is OK and if lzma decompression reaches EOF on input with the expected state (0==accumulator && bytes_written==original_length), then that is an integrity check that is broadly equivalent to crc32. lzma decompression is equivalent to a "arithmetic long division" of the input encoded representation; crc32 is a "polynomial long division" of the bitstring. The value added by crc32 is low. Because crc32 is orthogonal to the algorithmic check, then the probability that crc32 catches an otherwise-undetected error is 2**-32. The cost of crc32 is high. crc32 pollutes the data cache, often equivalent to flushing a major portion of L1. In the name of speed, common implementations use many kilobytes of tables. The adler32 checksum is *MUCH* better: no tables, less code, faster, no cache pollution. adler32 is about 1/4096 less powerful (65521/65536) in detecting impostors. crc32 is trivial in hardware and has mindshare. But in software, crc32 should be replaced by adler32. -- _______________________________________________ Anaconda-devel-list mailing list Anaconda-devel-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/anaconda-devel-list
