From help-request at octave dot org Sat Feb 12 14:33:25 2005
Subject: Re: Data types (was: Re: Access the neighbors of an element)
From: Paul Kienzle <pkienzle at users dot sourceforge dot net>
To: octave help mailing list <help at octave dot org>
Cc: Joerg Sommer <joerg at alea dot gnuu dot de>
Date: Sat, 12 Feb 2005 15:38:28 -0500

Some more details:

On MIPS it is faster to convert to double and perform the multiplication
than to convert to a wider integer and do it.

On X86 the gains from using integer operations are much bigger than for
MIPS or PPC.

Even bigger gains for X86 32-bit architectures and LONGLONG double 
multiplication are possible by casting the address of the value as
a pointer to two long integers:

# elif defined(LONGLONG)
#if defined(LITTLEENDIAN_32)
   unsigned long *px = &x, *py = &y;
   if ( (px[1] && (py[1] || px[1]*y > LO)) || (py[1] && (py[1]*x > LO)) )
#else
   if ((x > LO && (y > LO || (x>>HALF)*y > LO)) || (y>LO && (y>>HALF)*x 
 > LO))
#endif
     z = MX;
   else z = x * y;


- Paul



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