davidsen@steinmetz.ge.com (William E. Davidsen Jr) (05/05/88)
jpn@teddy.UUCP (John P. Nelson) writes: > >PKARC's SQUASH is 13 bit compression. Any more than this requires a >working buffer larger than 64K, which is why they are generally not used >very much on PCs. The amount of additional compression between 13 bit >and 16 bit is no more than 2 or 3 percent! > >Also, there is very little difference in speed between the 12 bit and >13 bit compression algorithms. The major difference is in the memory >requirements. As much as I agree with some of the other stuff you wrote, I think that the diference between 12, 13 and 16 bit compression is somewhat greater than that in at least some cases. Here are some figures from a compress test I ran a few minutes ago. <--- CPU ----> Final Bits User System Size 12 1:18.1 3.2 192854 13 1:14.1 3.0 182005 14 1:11.7 3.1 177321 15 1:16.4 2.8 173647 16 1:44.3 2.9 160648 Is 16 bit worth it? When considering the size of the original file, probably not. But when considering the size of the final file, is certainly is to me! For this large file (~500k) 16 bit was 20% better than 12 bit, and 13% better than 13 bit. Obviously the improvement gets smaller as the file gets smaller, becuse compress starts with 12 bit (or perhaps 10 bit) compression, and works up. On smaller files there's no gain because only 12 bits are used. BTW: actual file size 510962 bytes. Another set of numbers, for a binary file (mush 6.0 executable). original size 212062. bits user sys size 12 43.78 2.96 157916 16 58.00 2.88 134334 The 16 bit compression was about 14.9% smaller than the 12 bit. Obviously the results depend on both file size and content. -- bill davidsen (wedu@ge-crd.arpa) {uunet | philabs | seismo}!steinmetz!crdos1!davidsen "Stupidity, like virtue, is its own reward" -me