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From: ken@turtlevax.UUCP (Ken Turkowski)
Newsgroups: net.lang.c
Subject: Re: Falsies
Message-ID: <894@turtlevax.UUCP>
Date: Mon, 9-Sep-85 21:28:16 EDT
Article-I.D.: turtleva.894
Posted: Mon Sep  9 21:28:16 1985
Date-Received: Wed, 11-Sep-85 06:29:19 EDT
References: <1341@brl-tgr.ARPA>
Reply-To: ken@turtlevax.UUCP (Ken Turkowski)
Organization: CADLINC, Inc. @ Menlo Park, CA
Lines: 23
Keywords: Absolute truth

In article <1341@brl-tgr.ARPA> cottrell@NBS-VMS.ARPA (COTTRELL, JAMES) writes:
>@ In article <139200010@uiucdcsb> robison@uiucdcsb.Uiuc.ARPA writes:
>@ >> ... But no machine I know of has a `branch if true' instruxion...
>
>No, *I* wrote that. *He* responded.
>
>@ The 808x/Z80 families of microprocessors set the 'zero' flag in 'compare'
>@ instructions, and have 'jump if zero', 'jump if non-zero', as well as the
>@ corresponding conditional subroutine calls and and conditional returns.
>
>Don't you think I know that? Doesn't everybody? You missed the point 
>entirely! What I am saying is that at the assembly language level there
>is no notion of pure true or false as a primitive condition.

Wrong you are.  Look at the 68000 instruction set.  In it you'll find a
couple of instructions called DBT and DBF, which are "decrement and
branch on true" and "decrement and branch on false".  While not a pure
one condition branch (because of the decrement and test counter), the
assembly language does have a concept of absolute truth.
-- 
Ken Turkowski @ CADLINC, Menlo Park, CA
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