[sdcc-devel] [ sdcc-Bugs-604575 ] ptr ++ with cast and derref

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Bugs item #604575, was opened at 2002-09-04 12:22
Message generated for change (Comment added) made by felmasper
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Category: C-Front End
Group: fixed
Status: Open
Resolution: Fixed
Priority: 5
Submitted By: Felipe Massia Pereira (felmasper)
Assigned to: Johan Knol (johanknol)
Summary: ptr ++ with cast and derref

Initial Comment:
GCC compiles this in ANSI mode.

~/test $ cat ptr++.c
#include <stdio.h>

char x[4] = { 1, 2, 3, 4 };
int acc, i;
int *p;

void main() {

  acc = 0;
  p = (int *) x;

  for (i=0; i<2; i++)
    acc += *((int *)p)++;

  printf("%d\n",acc);
}

~/test $ sdcc -mz80 ptr++.c
ptr++.c:13: error: 'lvalue' required for '++' operation .
ptr++.c:15: error: code not generated for 'main' due to
previous errors



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>Comment By: Felipe Massia Pereira (felmasper)
Date: 2003-04-08 18:32

Message:
Logged In: YES 
user_id=387191

I compiled without -pedantic option. (gcc -ansi test.c)
This code snippet is, in fact, an IP checksum calculation
routine: sum the 1's complement of the 16-bit words. I
thought it was legal ANSI. I guess I have modified the code
a little from the original that I'm getting right now....
ok. Here it is.

static u32_t 
chksum(void *dataptr, int len)
{
  u32_t acc;
    
  for(acc = 0; len > 1; len -= 2) {
    acc += *((u16_t *)dataptr)++;
  }

  /* add up any odd byte */
  if(len == 1) {
    acc += htons((u16_t)((*(u8_t *)dataptr) & 0xff) << 8);
    DEBUGF(INET_DEBUG, ("inet: chksum: odd byte %d\n",
*(u8_t *)dataptr));
  }

  return acc;
}

This portion of code is supposed to be ANSI.

Copyright note: The above code snippet is from lwIP stack by
Adam Dunkels / SICS. 

Felipe


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Comment By: Johan Knol (johanknol)
Date: 2003-04-08 09:59

Message:
Logged In: YES 
user_id=63512

This needs a second thought, disabled the "fix" in 
SDCCicode.c:153


----------------------------------------------------------------------

Comment By: Nobody/Anonymous (nobody)
Date: 2003-04-08 08:53

Message:
Logged In: NO 

[tim@twlinux tim]$ gcc -Wall -ansi -pedantic test.c
test.c:8: warning: return type of `main' is not `int'
test.c: In function `main':
test.c:13: invalid lvalue in increment

How did you get this to compile with gcc?

----------------------------------------------------------------------

Comment By: Johan Knol (johanknol)
Date: 2003-04-08 08:00

Message:
Logged In: YES 
user_id=63512

fixed in SDCCicode.c:1.152

----------------------------------------------------------------------

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