Re: [boost] integer tests not working on 64 bit platforms

From: Jonathan Wakely (cow_at_[hidden])
Date: 2004-09-01 08:44:43

On Wed, Sep 01, 2004 at 12:50:32PM +0200, Markus Sch?pflin wrote:

> Currently the integer tests report an error on 64 bit platforms, as can be 
> seen on http://tinyurl.com/6whtg
> 
> The following code in integer_test.cpp causes the problem:
> 
>     PRIVATE_FIT_TESTS( int_t, least, long, LONG_MAX );
>     PRIVATE_FIT_TESTS( int_t, fast, long, LONG_MAX );
>     PRIVATE_FIT_TESTS( uint_t, least, unsigned long, ULONG_MAX );
>     PRIVATE_FIT_TESTS( uint_t, fast, unsigned long, ULONG_MAX );
> 
> The first line expands to:
> 
> do {
>   long v = LONG_MAX ;
>   PRIVATE_FIT_TEST(int_t, 32, least, v);
>   v >>= 1;
>   PRIVATE_FIT_TEST(int_t, 31, least, v);
>   v >>= 1;
>   ...
> }
> 
> which becomes:
> 
> do {
>   long v = LONG_MAX ;
>   BOOST_TEST( int_t < 32 > :: least ( v ) == v );
>   v >>= 1;
>   BOOST_TEST( int_t < 31 > :: least ( v ) == v );
>   v >>= 1;
>   ...
> }
> 
> which of course alway fails on 64 bit platforms because LONG_MAX is a 64 
> bit number.
> 
> A possible fix would be to start the test with 64 bit and not 32 on 64 bit 
> platforms. But how can 64 bit platforms be detected? Probably with #if 
> (LONG_MAX > INT_MAX) ... #endif or something like this.

This is not _guaranteed_ to work, but would be OK in practice.

An ILP64 platform would have sizeof(int) == sizeof(long) == 8
and an LLP64 platform would have sizeof(int) == sizeof(long) == 4

In both cases LONG_MAX == INT_MAX.

I think all 64-bit unices use the LP64 model, where sizeof(int) == 4 and
sizeof(long) == 8, so I think your suggestion would work.

> Another fix (which ignores 64 bit values alltogether) would be to change 
> the lines above to not use long and LONG_MAX but int and INT_MAX.

As I understand it that just changes the bad assumption that long is
32-bits to assuming that int is 32 (or fewer) bits, which is still an
unportable assumption, but likely to work for the foreseeable future
(famous last words :-)

jon

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