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3 points by almkglor 5857 days ago | link | parent

Actually it is, arc2c output crashes on my AMD64. I'm trying to hack out a replacement, but it's not working yet.

The problem is that apparently the bits of pointers that happen to be beyond the bits of ints are not zero, so assigning a pointer to an int chops off the significant bits.



1 point by sacado 5856 days ago | link

Oh... Maybe a simple fix would be to change int to long. I know this is not standard behavior, but in practice I think long and pointers are always the same size. mzscheme obviously works that way : every object is a pointer that you can cast to a long if it is a fixnum.

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2 points by almkglor 5856 days ago | link

This seems to be correct on my AMD64:

  #include<stdio.h>
  
  int main(void){
        printf("sizeof(int) = %d\n", sizeof(int));
        printf("sizeof(long) = %d\n", sizeof(long));
        printf("sizeof(void*) = %d\n", sizeof(void*));
        return 0;
  }

  sizeof(int) = 4
  sizeof(long) = 8
  sizeof(void*) = 8
However I think there may be processors/archs where sizeof(long) != sizeof(void* ). My attempt at fixing was to use a union, but something's wrong with the way closures are handled in my fix attempt - closures don't seem to have a type associated with them, so I'm not exactly sure how they're supposed to be done.

Edit: I'll probably need to search through C language specs, though - I'm not sure, but it might be standardized that sizeof(long) >= sizeof(void* )

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2 points by absz 5856 days ago | link

What you want are the two typedefs intptr_t and uintptr_t . Each one is defined to be an integer big enough to hold a pointer (the former being signed, and the latter being unsigned); they aren't mandatory, though, so you might have

  #if defined(__COMPILER1__) || defined(__COMPILER2__)
    typedef intptr_t fixnum;
  #else
    typedef long fixnum;
  #endif
This would guarantee you correct behaviour if intptr_t were defined, and probably give you the correct behaviour even if it weren't.

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1 point by almkglor 5856 days ago | link

From this?

  #include<stdint.h>
Hmm. Interesting. How well supported is it?

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1 point by sacado 5856 days ago | link

Thanks for the information ! I'll try it.

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