[TUHS] MacOS X is Unix (tm)

Ron Natalie ron at ronnatalie.com
Wed Jan 4 04:32:46 AEST 2017


> Microsoft still does and "True64" did use the ILP64 model. This allows
lazy written software to work even though it does not the right data types
for pointer arithmetic.
 
Well, there's a predisposition in C for "int" to be the standard word size
of the machine.    On designing for a 64-bit machine, one needs to think
long and hard about the integral sizes.
When we wrote the compilers for the Denelcor HEP, we had that problem.   The
thing had 64-bit words and a partial word mode for 16 and 32 bits.   It
didn't even have the concept of 8-bit math.
We decided that rather than arbitrarily sizing an int to 32, so we had the
char-short-int-long progression, we'd make it the word size.   This means we
had to introduce another keyword for the 32-bit type.
After dismissing "short long" or "long short" as a type, the suggestion was
"medium," but we settled for int32 (this was before the language standards
considered how to manage the system namespaces).

An amusing thing we found basing our code on 4.2 BSD was that there was a
really bad latent bug.     There was a kernel structure that looked like
this:

union  ptrs {
      int* p_int;
      short*  p_short;
      char* p_char;
      long* p_long;
};
   
The kernel would store one sort of pointer in one element and then retrieve
it from another.   This "conversion by union" didn't work on the HEP as the
word pointers had the partial word size encoded in the low order bits.
Reading out a short* where an int* was stored caused the processor to access
the wrong sized entity (though roughly in the proper location).    I had to
run all over the kernel changing those to a void* so that the generated code
could properly convert to the right pointer type.


Don't get me started on the inanity that states that "char" is the smallest
addressable integer.   Char should have been divorced from the integer
sizings and let be the native CHARACTER size alone.



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