How to get 64-bit intermediate results

[Richard Cavell]

Hi,

If I'm doing something like this:

#include<stdint.h>

uint64_t i = (0xffff * 0xffff ) ;

Or indeed any arbitrarily long expression, how do I ensure the
intermediate results won't be truncated to 32 bits without putting
irritating (uint64_t) casts next to each operand? And how do I get a
default sizeof(int) == 8 on an IA-64/G5?

 

[msalters]

Hi,

If I'm doing something like this:

#include<stdint.h>

uint64_t i = (0xffff * 0xffff ) ;

Wrong group, ask in comp.lang.c
( This is C99, in comp.lang.c++ only C++98/C++2003 are on-topic
and they are not based on C99 )

Regards,
Michiel Salters

 

[Richard Cavell]

Wrong group, ask in comp.lang.c
( This is C99, in comp.lang.c++ only C++98/C++2003 are on-topic
and they are not based on C99 )

Okay, then what's the equivalent C++ way to do it?

 

[Ioannis Vranos]

Hi,

If I'm doing something like this:

#include<stdint.h>

uint64_t i = (0xffff * 0xffff ) ;

Or indeed any arbitrarily long expression, how do I ensure the
intermediate results won't be truncated to 32 bits without putting
irritating (uint64_t) casts next to each operand? And how do I get a
default sizeof(int) == 8 on an IA-64/G5?

If your question is about C, you should ask in comp.lang.c.


If your question is .NET related (Visual C++ .NET) you should ask in
microsoft.public.dotnet.languages.vc newsgroup.

If it doesn't appear in your news server use the public MS news server:

msnews.microsoft.com

 

[msalters]

Okay, then what's the equivalent C++ way to do it?

unsigned long i = (0xffffUL*0xffffUL);

which will not overflow, but I don't see what 64 bits code has to
do with it. Besides, IIRC math base 2^32 doesn't care about overflows
on multiplications. ~0UL*~0UL==01UL, even if I use a 64-bits
intermediate.