Author: Dann Corbit
Date: 16:11:10 01/19/05
Go up one level in this thread
On January 19, 2005 at 17:56:42, Aaron Gordon wrote:
>On January 19, 2005 at 17:46:32, Dann Corbit wrote:
>
>>On January 19, 2005 at 17:27:57, Aaron Gordon wrote:
>>
>>>On January 19, 2005 at 11:55:43, Rémi Coulom wrote:
>>>
>>>>Hi,
>>>>
>>>>I am porting my chess program to 64 bit on an AMD64 Athlon processor. I have
>>>>noticed that, with gcc, sizeof(int)=4. I would have expected sizeof(int)=8. On
>>>>32-bit platforms, 32-bit variables are faster than 16-bit variables. I wonder if
>>>>64-bit variables are faster than 32-bit variables on 64-bit machines. I have
>>>>made a few experiments and did not notice much difference.
>>>>
>>>>Rémi
>>>
>>>Try using longs instead of ints. I have a DEC Alpha 21164 here (64bit also), and
>>>wondered the same thing. Here is the output I got when running sizeof().
>>>
>>>short = 2 (16 bits)
>>>int = 4 (32 bits)
>>>long = 8 (64 bits)
>>>long long = 8 (64 bits)
>>>float = 4 (32 bits)
>>>double = 8 (64 bits)
>>>
>>>On my Athlon XP, as expected, I get:
>>>short = 2 (16 bits)
>>>int = 4 (32 bits)
>>>long = 4 (32 bits)
>>>long long = 8 (64 bits)
>>>float = 4 (32 bits)
>>>double = 8 (64 bits)
>>
>>Depends on the compiler you use too.
>>
>>A compiler vendor can use any type they want for int, as long as it will hold
>>+/- 32767 or larger.
>
>The only ones I've tested so far have been GCC (DGJPP and MingW), the Intel C
>compiler, MSVC and the Compaq C compiler (for the Alpha). Though I think
>MSVC/Intel C (windows) uses __int64 instead of long/longlong. So far though it
>seems like all the linux compilers treat a long as 32bits unless you have a
>64bit cpu & 64bit compiler. I'm guessing/hoping it would be alright to just use
>longs from now on and if you have a 64bit cpu you'll just get the benefit from a
>recompile.
>
>Just wishful thinking perhaps ;)
On the Alpha (for instance) the DEC/COMPAQ/HP C++ compiler uses ints and longs
of 32 bits, like the MS compiler. For example:
$ cxx s.c
$ link s
$ run s
sizeof char is by definition 1. This machine reports 1
sizeof int is 4
sizeof long is 4
sizeof long long is 8
$ type s.c
#include <stdio.h>
int main(void)
{
printf("sizeof char is by definition 1. This machine reports %u\n",
(unsigned) sizeof (char));
printf("sizeof int is %u\n", (unsigned) sizeof (int));
printf("sizeof long is %u\n", (unsigned) sizeof (long));
#ifdef __GNUC__
printf("sizeof long long is %u\n", (unsigned) sizeof (long long));
#else
printf("sizeof long long is %u\n", (unsigned) sizeof (__int64));
#endif
return 0;
}
$
The GCC compiler on the same platform will report different values.
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