From: bs@fatima.mitre.org (Robert D. Silverman)
Newsgroups: comp.sys.powerpc,comp.arch.arithmetic,gnu.misc.discuss
Subject: Re: WANTED: algorithm to perform 64-bit / 32-bit signed & unsigned divide
Date: 7 Jul 1994 13:34:28 GMT
Organization: Research Computer Facility, MITRE Corporation, Bedford, MA
NNTP-Posting-Host: fatima.mitre.org
Keywords: integer divide

In article <joe.773514139@babel.ho.att.com> joe@sanskrit.ho.att.com (Joe Orost) writes:
>I'm looking for an algorithm to perform an integer 64-bit / 32-bit 
>signed divide, and a 64-bit / 32-bit unsigned divide on the PowerPC.
>I don't want to use the "DIV" instruction, which is not part of the 
 
#define	IBASE	1073741824
#define	BASE	(double)1073741824.0
 
/************************************************************************/
/*									*/
/*	Low level primitives for 64 bit arithmetic; portable version	*/
/*									*/
/************************************************************************/
 
 
/************************************************************************/
/*									*/
/*	mod_mul(a,b,c);  returns a * b mod c; a,b,c, unsigned 32 bit	*/
/*	integers							*/
/*									*/
/************************************************************************/
mod_mult(a,b,c)
unsigned long a,b,c;

{
register unsigned long quo,rem;

quo = (unsigned long)((double)a * (double)b/(double) c + .5);
rem = a*b - quo*c;
if ((long)rem <= -1) rem += c;
return(rem);
}

/************************************************************************/
/*									*/
/*	compute (a * b + c) / 2^30     and  (a * b + c) % 2^30		*/
/*									*/
/************************************************************************/
 
muladd(a,b,c,d)
unsigned long a,b,c,d[2];

{
register unsigned long rem,quo;
register double temp;

temp = (double)a * (double)b + (double)c;
quo = (unsigned long) (temp/BASE + .5);
rem = a*b + c - quo*IBASE;
if ((long)rem <= -1)
   {
   rem += IBASE;
   quo--;
   }
d[0] = rem;
d[1] = quo;
}

/************************************************************************/
/*									*/
/*	compute (a * b ) / 2^30     and  (a * b ) % 2^30		*/
/*									*/
/************************************************************************/
 
radmul(a,b,d)
unsigned long a,b,d[2];

{
register unsigned long rem,quo;
register double temp;

temp = (double)a * (double)b;
quo = (unsigned long) (temp/BASE + .5);
rem = a*b  - quo*IBASE;
if ((long)rem <= -1)
   {
   rem += IBASE;
   quo--;
   }
d[0] = rem;
d[1] = quo;
}
 
/************************************************************************/
/*									*/
/*	compute (a*2^30 + b)/c  and (a*2^30 + b) % c			*/
/*									*/
/************************************************************************/
divrem(a,b,c,d)
unsigned long a,b,c,d[2];

{
register unsigned long rem,quo;
register double temp;

temp = (double)a * BASE + (double)b;
quo = (unsigned long) (temp/(double) c + .5);
rem = a*IBASE + b - quo*c;
if ((long)rem <= -1)
   {
   rem += c;
   quo--;
   }
d[0] = quo;
d[1] = rem;
}
--
Bob Silverman
These are my opinions and not MITRE's.
Mitre Corporation, Bedford, MA 01730
"You can lead a horse's ass to knowledge, but you can't make him think"