• bearophile <bearophileHUGS lycos.com> Jan 27 2009
• Don <nospam nospam.com> Jan 27 2009
• Frits van Bommel <fvbommel REMwOVExCAPSs.nl> Jan 27 2009

bearophile <bearophileHUGS lycos.com> writes:

Walter Bright:
 Frits van Bommel:
 [1]: Hey, x86 technically has 6-byte pointers if you count segments as 
 part of the pointer (which would be mostly useless on currently popular 
 operating systems though).


 It does, but I know of no compiler that supports that (C, C++, or any 
 other), and code that needs to deal with that tends to be assembler.


16 free bits suggest various possible usages, for example the length for small
strings/arrays, halving the size of the array struct.

Bye,
bearophile

Don <nospam nospam.com> writes:

bearophile wrote:
 Walter Bright:
 Frits van Bommel:
 [1]: Hey, x86 technically has 6-byte pointers if you count segments as 
 part of the pointer (which would be mostly useless on currently popular 
 operating systems though).


 other), and code that needs to deal with that tends to be assembler.


 16 free bits suggest various possible usages, for example the length for small
strings/arrays, halving the size of the array struct.
 
 Bye,
 bearophile


They're not free bits. Those bits are in the segment registers, not in 
the pointer registers. Only the OS can change the segment registers. And 
it's a slow operation.

Frits van Bommel <fvbommel REMwOVExCAPSs.nl> writes:

bearophile wrote:
 Walter Bright:
 Frits van Bommel:
 [1]: Hey, x86 technically has 6-byte pointers if you count segments as 
 part of the pointer (which would be mostly useless on currently popular 
 operating systems though).


 other), and code that needs to deal with that tends to be assembler.


 16 free bits suggest various possible usages, for example the length for small
strings/arrays, halving the size of the array struct.


It's not that there are 16 extra bits available, it's that technically 
to specify a memory location you need to specify 16 more bits in one of 
a couple special registers. In practice though, these are pretty much 
always the same (or equivalent, at least).