Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10 5/3/83; site umcp-cs.UUCP Path: utzoo!watmath!clyde!floyd!harpo!seismo!rlgvax!cvl!umcp-cs!zben From: zben@umcp-cs.UUCP Newsgroups: net.arch Subject: Univac 1100 - Ones complement subtractive adder Message-ID: <4939@umcp-cs.UUCP> Date: Wed, 1-Feb-84 03:37:48 EST Article-I.D.: umcp-cs.4939 Posted: Wed Feb 1 03:37:48 1984 Date-Received: Tue, 7-Feb-84 09:20:31 EST Organization: Univ. of Maryland, Computer Science Dept. Lines: 17 > No, a one's complement subtractive adder is *not* a snake - there was one of 'em in the heart of the Univac 1108 that was my first and still most favorite computer (the maintenance on a 10+ year old machine was killing us so we scrapped it - sniff - I have one of the register boards in my desk drawer). Seems like normal hardware subtracts by complementing the subtrahend and adding. Well, this brain damaged hardware added by complementing one augend and subtracting! I think it ran marginally faster, but they might have been designing around a patent or something. In any case, it seemed to generate minus zeroes in a lot more cases than just (0)+(-0); you could generate a minus zero using normal operands. The Fortran compiler generated really contorted code to handle the case. I'm not sure if the current machines still have this problem, but that might explain the note from the Univac Unix person. Ben Cranston ...seismo!umcp-cs!zben zben@umd2.ARPA (running 4.1 BSD) (Univac 1100/80 but *not* running Unix (yet?) )