Received: (from major@localhost) by minnie.cs.adfa.oz.au (8.8.5/8.8.5) id KAA01382 for pups-liszt; Tue, 7 Apr 1998 10:43:25 +1000 (EST) X-Authentication-Warning: minnie.cs.adfa.oz.au: major set sender to owner-pups@minnie.cs.adfa.oz.au using -f Received: from renoir.op.net (root@renoir.op.net [209.152.193.4]) by minnie.cs.adfa.oz.au (8.8.5/8.8.5) with ESMTP id KAA01367 for ; Tue, 7 Apr 1998 10:43:10 +1000 (EST) Received: from goppelt.op.net (d-phlarc1-0c.ppp.op.net [209.152.199.76]) by renoir.op.net (o1/$Revision: 1.15 $) with SMTP id UAA07198; Mon, 6 Apr 1998 20:42:56 -0400 (EDT) Message-Id: <199804070042.UAA07198@renoir.op.net> Comments: Authenticated sender is From: "Ed G." To: pups@minnie.cs.adfa.oz.au, Bob Supnik Date: Mon, 6 Apr 1998 20:42:54 -0400 MIME-Version: 1.0 Content-type: Multipart/Mixed; boundary=Message-Boundary-396 Subject: Floating Point Bug in Bob's Emulator Reply-to: edgee@cyberpass.net X-mailer: Pegasus Mail for Win32 (v2.54) Sender: owner-pups@minnie.cs.adfa.oz.au Precedence: bulk --Message-Boundary-396 Content-type: text/plain; charset=US-ASCII Content-transfer-encoding: 7BIT Content-description: Mail message body I wrote a little square root program in "C" to test the floating point in Bob Supnik's emulator (see attached code). The program works fine under Linux, but bombs on Bob's emulator, confirming people's theory that the emulator has a floating point bug. I used Newton's method for the algorithm and only uses add, subtract, multiply and divide. The emulator produced identical incorrect results for two different versions of the program one using floats, the other doubles. Here's what the program does on Bob Supnik's emulator: # cc mysqrt.c # a.out Initial guess: 85070586659632214000000000000000000000.0000000000000000 guess: 1.0000000000000000 guess: 85070586659632214000000000000000000000.0000000000000000 guess: 1.0000000000000000 guess: 85070586659632214000000000000000000000.0000000000000000 guess: 1.0000000000000000 guess: 85070586659632214000000000000000000000.0000000000000000 guess: 1.0000000000000000 Here's what the program does on Linux: [root@oskar uv7]# gcc mysqrt.c [root@oskar uv7]# a.out Initial guess: 1.0000000000000000 guess: 1.5000000000000000 guess: 1.4166666666666667 guess: 1.4142156862745099 guess: 1.4142135623746899 My square root is: 1.4142135623746899 --Message-Boundary-396 Content-type: text/plain; charset=US-ASCII Content-disposition: inline Content-description: Attachment information. The following section of this message contains a file attachment prepared for transmission using the Internet MIME message format. If you are using Pegasus Mail, or any another MIME-compliant system, you should be able to save it or view it from within your mailer. If you cannot, please ask your system administrator for assistance. ---- File information ----------- File: MYSQRT.C Date: 6 Apr 1998, 23:50 Size: 413 bytes. Type: Program-source --Message-Boundary-396 Content-type: Application/Octet-stream; name="MYSQRT.C"; type=Program-source Content-disposition: attachment; filename="MYSQRT.C" Content-transfer-encoding: BASE64 I2RlZmluZSBQUkUgZG91YmxlCgpQUkUgYWJzdihuKQogIFBSRSBuOwp7CiAgaWYgKG4gPCAw KSB7CiAgICByZXR1cm4gLW47CiAgfQogIGVsc2UgewogICAgcmV0dXJuIG47CiAgfQp9CgpQ UkUgbXlzcXJ0KG4pClBSRSBuOwp7ClBSRSBnLCBlcnI7CgpnID0gbi8yOwplcnIgPSBuLzFl NjsKCnByaW50ZigiUHJlY2lzaW9uOiAgUFJFXG4iKTsKCnByaW50ZigiSW5pdGlhbCBndWVz czogJS4xNmZcblxuIiwgZyk7CiB3aGlsZSAoYWJzdihnKmctbikgPj0gZXJyKSB7CiAgIGcg PSAoZypnK24pLygyKmcpOwogICBwcmludGYoImd1ZXNzOiAlLjE2ZlxuIiwgZyk7CiB9CnJl dHVybihnKTsKfQoKbWFpbigpCnsKUFJFIG4gPSAyLjA7CgogcHJpbnRmKCJcbk15IHNxdWFy ZSByb290IGlzOiAlLjE2ZlxuIiwgbXlzcXJ0KG4pKTsKfQo= --Message-Boundary-396--