🚀 go-pugleaf

This bug report is for GNU tar versions 1.10 and 1.11.

Different versions of tar seem to compute header checksums differently.  I
suspect that the original tar code added up a bunch of "char" values, which
were unsigned on the PDP-11 and that the code was never changed when signed
chars were introduced.  The following patch causes GNU tar to be a little more
forgiving when it tries to read tar archives created with /bin/tar on Nexts,
Suns, and others.


*** list.c.~1~	Tue Sep  8 16:22:38 1992
--- list.c	Thu Sep 10 15:47:56 1992
***************
*** 289,295 ****
  read_header()
  {
  	register int	i;
! 	register long	sum, recsum;
  	register char	*p;
  	register union record *header;
  	long	from_oct();
--- 289,295 ----
  read_header()
  {
  	register int	i;
! 	register long	sum, signed_sum, recsum;
  	register char	*p;
  	register union record *header;
  	long	from_oct();
***************
*** 314,326 ****
  		 * We can't use unsigned char here because of old compilers,
  		 * e.g. V7.
  		 */
  		sum += 0xFF & *p++;
  	}
  
  	/* Adjust checksum to count the "chksum" field as blanks. */
  	for (i = sizeof(header->header.chksum); --i >= 0;)
  		sum -= 0xFF & header->header.chksum[i];
! 	sum += ' '* sizeof header->header.chksum;	
  
  	if (sum == 8*' ') {
  		/*
--- 314,331 ----
  		 * We can't use unsigned char here because of old compilers,
  		 * e.g. V7.
  		 */
+ 	        signed_sum += *p;
  		sum += 0xFF & *p++;
  	}
  
  	/* Adjust checksum to count the "chksum" field as blanks. */
  	for (i = sizeof(header->header.chksum); --i >= 0;)
+ 	{
  		sum -= 0xFF & header->header.chksum[i];
! 		signed_sum -= (char) header->header.chksum[i];
! 	}
! 	sum += ' ' * sizeof header->header.chksum;
! 	signed_sum += ' ' * sizeof header->header.chksum;
  
  	if (sum == 8*' ') {
  		/*
***************
*** 330,336 ****
  		return 2;
  	}
  
! 	if (sum != recsum) 
  	  return 0;
  	
  	/*
--- 335,341 ----
  		return 2;
  	}
  
! 	if (sum != recsum && signed_sum != recsum)
  	  return 0;
  	
  	/*