Re: [boost] A pure C/C++ question

From: Victor A. Wagner, Jr. (vawjr_at_[hidden])
Date: 2002-08-21 01:39:05

At Tuesday 2002/08/20 21:45, you wrote:
>The question of how to support the double word results of
>multiplying two words ecently came up on the C++ committee
>reflector.  The choices seem to be either providing a special
>function, or providing typedefs for which idioms like the
>following can result in optimal code:
>
>    uword_t x, a;
>    ulong_t y = ulong_t(x) * a;
>
>To which we can add:
>    uword_t b;
>    ulong_t y = ulong_t(x) * a / b;
>
>I should think that most compilers already do a good job,
>given suitable choices of uword_t and ulong_t, but I haven't
>done any testing to find out.

This is also one of my pet peeves about a language that purportedly lets 
you code "down to the sand".
also missing is the concept of carry or overflow that is readily detectable 
at the language level.
The _real_ problem isn't addressed by Band-Aids like the BCPL muldiv(x, a, 
b) but at least THAT language had it as part of the standard library.
The problem is exactly like every other problem we have in this biz.... 
someone got there "first with the worst" and we can't recover from it.  The 
_only_ reasonable thing would be to make the expression   y = x * a / b; 
work like it does when you code it in assembly on most machines.
BUT.... that wouldn't be backwards compatible, so we're stuck with "worst".

If the committee is seriously considering ways to handle stuff, how about 
dealing with the two results returned by almost every integer divide 
instruction... quotient and remainder.

[deleted]
Victor A. Wagner Jr.      http://rudbek.com
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