BUG in Ada compiler?

BUG in Ada compiler?

[Bob Argyle]

greetings Ada wizards, 

The following program on a VAX 8700 prints out:
"Hello, your program is exceptional!"
but if I change either 32767 to 32768, it runs fine: "Hello, World"
Two questions: 1. Am I overlooking something very basic?  Or, 
2.  Is the compiler here broken? Is _yours_?

with text_io; use text_io;
procedure bug is
   m:array (0..32767,0..32767) of character;
   begin
      m(0,8) := 'c';
      put("Hello, ");
      m(1,8) := 'c';
      put_line("World");
   exception
      when numeric_error | constraint_error => 
         put_line("numeric_error | constraint_error"); 
         -- must have same handler or compiler complains.
      when program_error => put_line("program_error");
      when storage_error => put_line("storage_error");
      when tasking_error => put_line("tasking_error");
      when data_error	 => put_line("data_error");
      when status_error	 => put_line("status_error");
      when mode_error	 => put_line("mode_error");
      when name_error	 => put_line("name_error");
      when use_error	 => put_line("use_error");
      when device_error	 => put_line("device_error");
      when end_error	 => put_line("end_error");
      when layout_error	 => put_line("layout_error");
      when others 	 => put_line("your program is exceptional!");
      -- no known named exception raised
   end bug;

-- 
bob argyle @ wsccs      void where prohibited.  int where not declared.
#ifndef disclaimer
	/*
#endif

Re: BUG in Ada compiler?

[Robert Firth]

In article <781@wsccs.UUCP> rargyle@wsccs.UUCP (Bob Argyle) writes:

>The following program on a VAX 8700 prints out:
>"Hello, your program is exceptional!"
>but if I change either 32767 to 32768, it runs fine: "Hello, World"
>Two questions: 1. Am I overlooking something very basic?  Or, 
>2.  Is the compiler here broken? Is _yours_?
>
>with text_io; use text_io;
>procedure bug is
>   m:array (0..32767,0..32767) of character;
>   begin
>      m(0,8) := 'c';
>      put("Hello, ");
>      m(1,8) := 'c';

[at which point the exception occurs]

The program is legal (though certainly exceptional), and so one suspects
that the compiler has a bug here.

Wild conjecture: as shown, the array M has an index type that is
implicitly WORD, ie 16 bits.  The compiler expands the two-dimensional
array index expression by the multiplicative method into

	(mbase + index1 * stride + index2)

Because the indices are considered to be of type word, the compiler
resolves the "*" and "+" operations to be also of type word, ie 16
bits.  This works by sheer chance for the first expression, which stays
within 16-bit range, but blows up on the second expression.

If the upper bounds are changed to 32768 the index type becomes
implicitly longword, which works.

Source of problem: the premature expansion of the array index expression
before overload resolution, followed by application of Ada's resolution
rules to an expression that isn't in Ada and shouldn't follow those rules.

Hope that helps - remember: a wild conjecture, no more.

Re: BUG in Ada compiler?

[Jim Near]

/ hpclove:comp.lang.ada / rargyle@wsccs.UUCP (Bob Argyle) /  6:48 pm  Nov 10, 1988 /

greetings Ada wizards, 

The following program on a VAX 8700 prints out:
"Hello, your program is exceptional!"
but if I change either 32767 to 32768, it runs fine: "Hello, World"
Two questions: 1. Am I overlooking something very basic?  Or, 
2.  Is the compiler here broken? Is _yours_?

with text_io; use text_io;
procedure bug is
   m:array (0..32767,0..32767) of character;
   begin
      m(0,8) := 'c';
      put("Hello, ");
      m(1,8) := 'c';
      put_line("World");
   exception
      when numeric_error | constraint_error => 
         put_line("numeric_error | constraint_error"); 
         -- must have same handler or compiler complains.
      when program_error => put_line("program_error");
      when storage_error => put_line("storage_error");
      when tasking_error => put_line("tasking_error");
      when data_error	 => put_line("data_error");
      when status_error	 => put_line("status_error");
      when mode_error	 => put_line("mode_error");
      when name_error	 => put_line("name_error");
      when use_error	 => put_line("use_error");
      when device_error	 => put_line("device_error");
      when end_error	 => put_line("end_error");
      when layout_error	 => put_line("layout_error");
      when others 	 => put_line("your program is exceptional!");
      -- no known named exception raised
   end bug;

-- 
bob argyle @ wsccs      void where prohibited.  int where not declared.
#ifndef disclaimer
	/*
#endif
----------