Path: utzoo!attcan!uunet!snorkelwacker!usc!cs.utexas.edu!rice!sun-spots-request
From: tac@cs.brown.edu (Theodore A. Camus)
Newsgroups: comp.sys.sun
Subject: Re: Integer math on SPARCs
Keywords: Miscellaneous
Message-ID: <8148@brazos.Rice.edu>
Date: 24 May 90 17:57:27 GMT
Sender: root@rice.edu
Organization: Sun-Spots
Lines: 21
Approved: Sun-Spots@rice.edu
X-Refs:  Original: v9n178
X-Sun-Spots-Digest: Volume 9, Issue 182, message 4

> Whenever two integer variables are multiplied together, the assembly 
> code generated by the C compiler (both Sun's and gcc) generate the line:
>
>		call	.mul, 2
>
> rather than use the integer multiply operation. Why is that? Floating
> point multiplies generate an fmuld assembler instruction. What's going on?

Simple - in keeping with the RISC philosophy, there is no integer multiply
instruction on the SPARC ALU.  The ".mul" routine computes multiplication
literally by shifts and adds, just like we learned in 3rd grade.  There is
actually a "mulscc" instruction which does a shift and add in a single
cycle.  (There is also a .umul for unsigned multiplication, as well as
.div, .udiv, .rem, and .urem.)

- Ted

  CSnet:     tac@cs.brown.edu                          Ted Camus  
  ARPAnet:   tac%cs.brown.edu@relay.cs.net             Box 1910 CS Dept
  BITnet:    tac@browncs.BITNET                        Brown University
  "An ounce of example is worth a pound of theory."    Providence, RI 02912