From owner-freebsd-arch Tue Jul 25 23:42:41 2000 Delivered-To: freebsd-arch@freebsd.org Received: from freefall.freebsd.org (freefall.FreeBSD.ORG [204.216.27.21]) by hub.freebsd.org (Postfix) with ESMTP id 49B9337B697; Tue, 25 Jul 2000 23:42:39 -0700 (PDT) (envelope-from kris@FreeBSD.org) Received: from localhost (kris@localhost) by freefall.freebsd.org (8.9.3/8.9.2) with ESMTP id XAA60024; Tue, 25 Jul 2000 23:42:39 -0700 (PDT) (envelope-from kris@FreeBSD.org) X-Authentication-Warning: freefall.freebsd.org: kris owned process doing -bs Date: Tue, 25 Jul 2000 23:42:39 -0700 (PDT) From: Kris Kennaway To: "Jeroen C. van Gelderen" Cc: arch@freebsd.org Subject: Re: Quantifying entropy In-Reply-To: Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-freebsd-arch@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG On Sat, 22 Jul 2000, Kris Kennaway wrote: > Some interesting numbers: > > The shannon entropy of this sample as a pure probability distribution is > 8.50 bits/sample (they're 16-bit signed values). > > Compressing with gzip -9 and comparing the file sizes gives an entropy > estimate of 10.4 bits/sample. > > Compressing with bzip2 -9 gives an estimate of 7.90 bits/sample, > suggesting there is indeed some time-correlation in the signal noise. Actually I just worked out why bzip2 gave this result: bzip2 treats the data as an 8-bit source, and from that perspective my data has 7.92 bits of entropy per 16-bits :-) (because the spectrum is peaked around 320 (when interpreted as unsigned 16-bit quantities), every second byte is most likely to be an '00' or '01', thus skewing the 8-bit distribution) Kris -- In God we Trust -- all others must submit an X.509 certificate. -- Charles Forsythe To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-arch" in the body of the message