Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.3 4.3bsd-beta 6/6/85; site turtlevax.UUCP
Path: utzoo!watmath!clyde!burl!ulysses!allegra!mit-eddie!genrad!decvax!decwrl!turtlevax!ken
From: ken@turtlevax.UUCP (Ken Turkowski)
Newsgroups: net.lang.c
Subject: Re: C Floating point arithmetic
Message-ID: <984@turtlevax.UUCP>
Date: Thu, 5-Dec-85 15:31:47 EST
Article-I.D.: turtleva.984
Posted: Thu Dec  5 15:31:47 1985
Date-Received: Sat, 7-Dec-85 21:06:14 EST
References: <706@lasspvax.UUCP> <7849@ucla-cs.ARPA>
Reply-To: ken@turtlevax.UUCP (Ken Turkowski)
Distribution: net
Organization: CIMLINC, Inc. @ Menlo Park, CA
Lines: 24

In article <7849@ucla-cs.ARPA> jimc@ucla-cs.UUCP (Jim Carter) writes:
>    As for short-int-long conversions, I don't know of any machines where
>loading 16 bits into a 32-bit register is any slower than loading 32 bits.

However, if an int is a long, and your C compiler does all operations
on longs, then it takes at least one extra instruction to either sign-
or zero-extend a short or char to a long. So to add two shorts, you have:
	move16	_a,r0
	ext32	r0
	move16	_b,r1
	ext32	r1
	add32	r1,r0
	move16	r0,_a
Rather than
	move16	_a,r0
	add16	_b,r0
	move16	r0,_a
Or
	add16	_b,_a
Can you say "order of magnitude in speed difference"?
-- 
Ken Turkowski @ CIMLINC, Menlo Park, CA
UUCP: {amd,decwrl,hplabs,seismo,spar}!turtlevax!ken
ARPA: turtlevax!ken@DECWRL.DEC.COM