Re: pointer calculations

Page alignment can be important to performance.

If your program is created with options STGMDL(*SNGLVL) and DTAMDL(*P128)
[these are the defaults and they instruct the compiler to build a program
that allocates its working storage from single-level storage and uses
16-byte pointers], you must calculate an increment and add it to the
pointer.  For example, to round a pointer up to the next page boundary, you
can try something like this:

#include <mih/lspco.h>  /* _LSPCO -- load space origin  */

#define NEXT_PAGE(p) ( (char *)_LSPCO(p) \
              + (((p - (char*)_LSPCO(p)) + (PAGESIZE-1)) &
(~(PAGESIZE-1))) )

The page size is 4096 on current AS/400 and iSeries models, but it can also
be materialized with the MATRMD MI instruction.

If your program is created with options TERASPACE(*YES) STGMDL(*TERASPACE)
DTAMDL(*LLP64) [these instruct the compiler to build a program that
allocates its working storage from Teraspace and uses 8-byte pointers], you
can effectively treat the pointer like an integer, although pointers are the
same size as "long long" integers.

To round an 8-byte pointer up to the next page boundary, you can try
something like this:

#define NEXT_PAGE(p) \
         (char*)( (long long)( (char*)p + (PAGESIZE-1) ) & (~(PAGESIZE-1)) )



"Terrence Enger" <tenger@xxxxxxxxxxxxxxxx> wrote in
message news:3.0.3.32.20030901191529.00ce4c50@xxxxxxxxxxxxxx
> If so, is there a portable type which defines an integer at least large
> enough to hold an address?  Can I cast an integer expression to a pointer,
> or do I have to calculate an increment and add it to the pointer?