[GiNaC-list] Possible size issue in test in numeric.cpp

[Pierangelo Masarati]

Jens Vollinga writes: 

>> I agree it should be
>>       i < ((1UL << cl_value_len)-1)
> 
> well, I have to correct myself: it should be
>        i < (1UL << cl_value_len)
> I guess.

Right, sorry.  I obviously had <= in mind :) 

> 
> But still I want to wait for Richy's response before I put it in CVS, 
> because it could be that CLN uses a signed data representation for small 
> integers internally (crazy idea, but conceivable ... ;-)) so that the 
> original if clause might be correct. 
> 

Looking at recent CLN stuff, I see that the internal representation of any 
type of data is a word, which is basically a "cl_uint" (in cln/object.h: 

typedef uintP  cl_uint;  // This ought to be called `cl_word'. 

where 

 typedef unsigned long  uintP; 

:) 

It doesn't really care about signedness until the value is extracted and 
shifted back to its position. 

I haven't looked into CLN's CVS yet, though, but this looks like something 
that shouldn't change quite often.  However, since applications using CLN 
shouldn't be aware of those details, I'm getting convinced that the 
optimization you're trying to obtain in numeric.cpp should actually be moved 
to CLN, in the sense that being CLN a likely candidate as a building block 
for higher-level numerical libraries (like GiNaC, for example), it should 
provide means for safe and efficient machine and OS independent conversion 
between its internal representation and built-in types.  Details about how 
to implement it are beyond the scope of this message; it could be by 
providing standard limits for the builtin types (like INT_MAX, UNIT_MAX and 
so in limits.h) or a test (sort of SAFE_CAST_TO_INT(x), SAFE_CAST_TO_UINT(x) 
and similar) or so. 

Cheers, p. 

Dr. Pierangelo Masarati               | voice: +39 02 2399 8309
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