Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!decwrl!hplabs!hpda!hpcuhb!hpcllla!hpclisp!hpclkwp!karl
From: karl@hpclkwp.HP.COM (Karl Pettis)
Newsgroups: comp.arch
Subject: Re: Endian reversing MOVEs
Message-ID: <650007@hpclkwp.HP.COM>
Date: 13 Feb 89 23:05:10 GMT
References: <759@atanasoff.cs.iastate.edu>
Organization: Hewlett-Packard Calif. Language Lab
Lines: 27

On the Hewlett-Packard Precision Architecture, reversing the bytes in
a word can be done in three instructions:

                                ;       r1 = "ABCD"
        SHD     r1,r1,16,r2     ;       r2 = "CDAB"
        DEP     r2,15,8,r2      ;       r2 = "CBAB"
        SHD     r1,r2,8,r2      ;       r2 = "DCBA"

Explanation:

        SHD     r1,r2,p,t       ;       Shift Double

          Concatenates r1 and r2 and shifts the combination right by
          p bits, putting the low 32 bits of the result into t.

        DEP     r,p,len,t       ;       Deposit

          Takes the len low order bits of r and places them into
          register t with the least significant bit at position p.
          Other bits of t are unchanged.

HPPA numbers bits in a word in big-endian order:  0..31.

This code was devised by Jerry Huck.  I'm just posting it.

- Karl Pettis
karl@hpda