I think the (old) reason of the way Sys.word_size is implemented is that
the same code can run both on 32 bits and 64 bits, when compiled to
bytecode. But of course, I see no reason why such a primitive could not
be added, with different compilation schemes for asm (it would be hard
coded) and bytecode (it would continue to call the runtime function).

Fabrice


On 09/06/2011 12:11 AM, John Carr wrote:
> I found a simpler way to make Sys.word_size be a compile time constant.
> See patch at end.  Technically this is preprocessing, which I wanted to
> avoid, but it's not preprocessing in my code.
> 
>> INRIA developers, is it easy to add an intrinsic so we can write
>>
>> 	extern word_size : int = "%caml_word_size"
>>
>> in sys.ml?  If sys.cmx has a constant definition, ocamlopt should do
>> constant folding on conditional expressions testing Sys.word_size.
> 
> 
> diff -rc /tmp/ocaml-3.12.1/stdlib/Makefile.shared ./stdlib/Makefile.shared
> *** /tmp/ocaml-3.12.1/stdlib/Makefile.shared	Fri May 21 07:28:21 2010
> --- ./stdlib/Makefile.shared	Mon Sep  5 17:39:14 2011
> ***************
> *** 49,56 ****
>   stdlib.cmxa: $(OBJS:.cmo=.cmx)
>   	$(CAMLOPT) -a -o stdlib.cmxa $(OBJS:.cmo=.cmx)
>   
> ! sys.ml: sys.mlp ../VERSION
> ! 	sed -e "s|%%VERSION%%|`sed -e 1q ../VERSION`|" sys.mlp >sys.ml
>   
>   clean::
>   	rm -f sys.ml
> --- 49,57 ----
>   stdlib.cmxa: $(OBJS:.cmo=.cmx)
>   	$(CAMLOPT) -a -o stdlib.cmxa $(OBJS:.cmo=.cmx)
>   
> ! sys.ml: sys.mlp ../VERSION ../config/m.h
> ! 	ws=`sed -n -e 's/^#define ARCH_SIXTYFOUR/64/p' -e 's/^#undef ARCH_SIXTYFOUR/32/p' ../config/m.h`; \
> ! 	sed -e "s|%%VERSION%%|`sed -e 1q ../VERSION`|" -e "s|%%WORD_SIZE%%|$$ws|" sys.mlp >sys.ml
>   
>   clean::
>   	rm -f sys.ml
> diff -rc /tmp/ocaml-3.12.1/stdlib/sys.mlp ./stdlib/sys.mlp
> *** /tmp/ocaml-3.12.1/stdlib/sys.mlp	Mon Feb 26 09:21:57 2007
> --- ./stdlib/sys.mlp	Mon Sep  5 17:35:33 2011
> ***************
> *** 23,29 ****
>   external get_argv: unit -> string * string array = "caml_sys_get_argv"
>   
>   let (executable_name, argv) = get_argv()
> ! let (os_type, word_size) = get_config()
>   let max_array_length = (1 lsl (word_size - 10)) - 1;;
>   let max_string_length = word_size / 8 * max_array_length - 1;;
>   
> --- 23,30 ----
>   external get_argv: unit -> string * string array = "caml_sys_get_argv"
>   
>   let (executable_name, argv) = get_argv()
> ! let (os_type, _) = get_config()
> ! let word_size = %%WORD_SIZE%%;;
>   let max_array_length = (1 lsl (word_size - 10)) - 1;;
>   let max_string_length = word_size / 8 * max_array_length - 1;;
>   
>