[SOLVED] double size ints in C

Skaperen · 03-04-2012, 08:12 PM

On 32 bit architectures, GCC provided 64 bit integer types, with compiled code generally calling some function to do the work, though I do remember seeing this compiled in-line somewhere at one time (maybe a different version or a different compiler or a different architecture ... I have worked with ARM, MIPS, and PPC as well as x86).

Conclusion: it is not that hard to do the steps to implement double sized int arithmetic by a compiler.

So what about doing 128 bit integers on a 64 bit architecture with similar code? That doesn't seem to be implemented in GCC, or if it is, requires some special setting or header to make it (or the types) available. Anyone know how to do this? I'm wanting to avoid using a GMP or similar library for the 128 bit case, and let me just code it like normal arithmetic in C.

orgcandman · 03-05-2012, 01:48 PM

Code:

aconole@aconole-azilap:~$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/4.6.1/lto-wrapper
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu/Linaro 4.6.1-9ubuntu3' --with-bugurl=file:///usr/share/doc/gcc-4.6/README.Bugs --enable-languages=c,c++,fortran,objc,obj-c++,go --prefix=/usr --program-suffix=-4.6 --enable-shared --enable-linker-build-id --with-system-zlib --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.6 --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --enable-plugin --enable-objc-gc --disable-werror --with-arch-32=i686 --with-tune=generic --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 4.6.1 (Ubuntu/Linaro 4.6.1-9ubuntu3) 
aconole@aconole-azilap:~$ cat double_int.c
#include <stdio.h>

int main(int argc, char *argv[])
{
    __int128 a = 0;

    a += 1590;
    
    printf("sizeof(__int128) = %lu\n", sizeof(a));

    return 0;
}
aconole@aconole-azilap:~$ gcc -o double_int double_int.c
aconole@aconole-azilap:~$ ./double_int 
sizeof(__int128) = 16
aconole@aconole-azilap:~$

Does this help?

Skaperen · 03-05-2012, 04:06 PM

Quote:

Originally Posted by orgcandman

Code:

aconole@aconole-azilap:~$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/4.6.1/lto-wrapper
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu/Linaro 4.6.1-9ubuntu3' --with-bugurl=file:///usr/share/doc/gcc-4.6/README.Bugs --enable-languages=c,c++,fortran,objc,obj-c++,go --prefix=/usr --program-suffix=-4.6 --enable-shared --enable-linker-build-id --with-system-zlib --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.6 --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --enable-plugin --enable-objc-gc --disable-werror --with-arch-32=i686 --with-tune=generic --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 4.6.1 (Ubuntu/Linaro 4.6.1-9ubuntu3) 
aconole@aconole-azilap:~$ cat double_int.c
#include <stdio.h>

int main(int argc, char *argv[])
{
    __int128 a = 0;

    a += 1590;
    
    printf("sizeof(__int128) = %lu\n", sizeof(a));

    return 0;
}
aconole@aconole-azilap:~$ gcc -o double_int double_int.c
aconole@aconole-azilap:~$ ./double_int 
sizeof(__int128) = 16
aconole@aconole-azilap:~$

Does this help?

Sort of. Looks like gcc 4.4.5 in my Ubuntu 10.10 doesn't have this.

Code:

lorentz/phil /home/phil 70> cat biggerint.c
#include <stdio.h>

int main(int argc, char *argv[])
{
    __int128 a = 0;

    a += 1590;
    
    printf("sizeof(__int128) = %lu\n", sizeof(a));

    return 0;
}
lorentz/phil /home/phil 71> gcc -o biggerint biggerint.c
biggerint.c: In function 'main':
biggerint.c:5: error: '__int128' undeclared (first use in this function)
biggerint.c:5: error: (Each undeclared identifier is reported only once
biggerint.c:5: error: for each function it appears in.)
biggerint.c:5: error: expected ';' before 'a'
biggerint.c:7: error: 'a' undeclared (first use in this function)
lorentz/phil /home/phil 72> find /usr/include -type f -exec fgrep -l __int128 '{}' ';'
lorentz/phil /home/phil 73>

Well, at least I now know WHAT to check for in a future version of gcc if I can get a usable desktop set up on a newer Ubuntu or convert everything I have over to another distro. Any idea just which version of gcc this started working?

orgcandman · 03-06-2012, 08:48 AM

I'm not exactly sure when it was "blessed" by the gcc community, but it seems that a preliminary patch was delivered in Jan 2010.

All my reading seems to indicate it is in GCC 4.6+

Skaperen · 03-06-2012, 12:24 PM

Quote:

Originally Posted by orgcandman

I'm not exactly sure when it was "blessed" by the gcc community, but it seems that a preliminary patch was delivered in Jan 2010.

All my reading seems to indicate it is in GCC 4.6+

Thanks for the info. Ubuntu Oneiric (11.10) seems to be where 4.6 begins to be available. Slackware does not have 4.6, yet (maybe whatever follows 13.37 will have it).