The deflation algorithm used by zip and gzip is a variation of LZ77 (Lempel-Ziv 1977, see reference below). It finds duplicated strings in the input data. The second occurrence of a string is replaced by a pointer to the previous string, in the

c lz77 simple-lz77.c -- Simple LZ77 (Ziv-Lempel) encoding [compression] with ** fixed offset/legth sizes [fixed size window of 4096 {2**12} bytes, ** match lengths of 15 {2**4-1} bytes] and alternating pointers into the

TIFF Library. Rev 5.0 Lempel-Ziv & Welch Compression Support Source Code for Linux.