Path: utzoo!utgpu!water!watmath!clyde!att-cb!ihnp4!alberta!calgary!radford
From: radford@calgary.UUCP (Radford Neal)
Newsgroups: comp.arch
Subject: Re: Auto-shifted registers
Message-ID: <1391@vaxb.calgary.UUCP>
Date: 25 Feb 88 23:35:08 GMT
References: <1370@vaxb.calgary.UUCP> <6310005@hpcupt1.HP.COM>
Organization: U. of Calgary, Calgary, Ab.
Lines: 14

In article <6310005@hpcupt1.HP.COM>, viggy@hpcupt1.HP.COM (Viggy Mokkarala) writes:

> The HP Precision Architecture provides for these kinds of operations by its
> Shift and Add instructions.  There is a pre-shifter before one of the inputs to
> the CPU.  It allows for one of the operands to be pre-shifted by upto 3 bits
> before an addition happens. 

Does this cost you anything (other than chip area), or does the shift
overlap another operation? If it does overlap, is there any reason
not to allow it for all relevant instructions (e.g. and and or)?
Is there any reason to keep the unshifted add (given a shift of zero 
is possible)?

    Radford Neal