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From: Georg Bauhaus <sb463ba@l1-hrz.uni-duisburg.de>
Newsgroups: comp.lang.ada
Subject: Re: What is faster Ada or C?
Date: Mon, 3 Dec 2001 20:56:12 +0000 (UTC)
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Ted Dennison <dennison@telepath.com> wrote:
 
: That was "hello world", I believe. I think he actually posted that example at
: one point many years back. It sort of cheated, in that it pragma-interface'd to
: C for stuff like the IO routines. But then again, there's nothing stopping you
: from doing that too if you really want to. :-)
: 


For fun I've tried to check this several times myself; here is one
program in C and Ada, without optimization, that shows essentially
no difference. Differences have usually vanished when I had asked
for optimisation. OTOH, if you follow the assembly output below,
they aren't that significant anyway. The programs have been compiled
with gcc -S and gcc -S -gnatp respectively.

function Silly return Integer is

   Result: Integer:= 0;

begin
   for K in 1..1000 loop
      Result:= Result + 1;
   end loop;

   return Result;
end Silly;


int silly()
{
  int result = 0, k;

  for (k = 1; k <= 1000; k++)
    {
      result++;
    }

  return result;
}


Here is side by side output:

        .file   "silly.adb"             .file   "silly.c"
gcc2_compiled.:                    gcc2_compiled.:
___gnu_compiled_ada:               ___gnu_compiled_c:
.text                              .text
        .align 4                        .align 4
.globl __ada_silly                 .globl _silly
__ada_silly:                       _silly:
        pushl %ebp                      pushl %ebp
        movl %esp,%ebp                  movl %esp,%ebp
        subl $8,%esp                    subl $8,%esp
        movl $0,-4(%ebp)                movl $0,-4(%ebp)
        movl $1,-8(%ebp)                movl $1,-8(%ebp)
L2:                                L2:
        cmpl $1000,-8(%ebp)             cmpl $1000,-8(%ebp)
        jle L5                          jle L5
        jmp L3                          jmp L3
        .align 2,0x90                   .align 2,0x90
L5:                                L5:
        incl -4(%ebp)                   incl -4(%ebp)
        jmp L4                     L4:
        .align 2,0x90                   incl -8(%ebp)
        jmp L3                          jmp L2
        .align 2,0x90                   .align 2,0x90
L6:                                L3:
L4:                                     movl -4(%ebp),%edx
        incl -8(%ebp)                   movl %edx,%eax
        jmp L2                          jmp L1
        .align 2,0x90                   .align 2,0x90
L3:                                L1:
        movl -4(%ebp),%edx              movl %ebp,%esp
        movl %edx,%eax                  popl %ebp
        jmp L1                          ret
        .align 2,0x90
L1:
        movl %ebp,%esp
        popl %ebp
        ret

The optimiser's output is also quite interesting :-)

Georg