Checksum incorrectly uses signed values

Hi,

I initially reported this issue to another developer thinking the issue resided there but after some testing and discussion, have found that the issue is not there but possibly here :)

The issue, in summary, is that 7-zip was unable to untar a tar created via a "git archive" whereas gnu tar can. It seem that it may be the case that git is incorrectly using signed values when creating the checksum.

As Igor commented in the other aforementioned thread, "[t]hey use 'char' (that is 'signed char' by default in most compilers). BUT correct TAR must use sum of unsigned values."

Please see the following:

1) The thread previously opened with Igor/7-Zip:
http://sourceforge.net/projects/sevenzip/forums/forum/45798/topic/5322604
2) http://www.gnu.org/software/tar/manual/html_node/Checksumming.html
3) TAR source code:
     tar_checksum
      and
     simple_finish_header
      functions.
4) GIT source code that calculates checksum: ustar_header_chksum
function in archive-tar.c. For reference, here is the snippet of the
git source code in question:

git-git-f623ca1\archive-tar.c
static unsigned int ustar_header_chksum(const struct ustar_header *header)
{
       const char *p = (const char *)header;
       unsigned int chksum = 0;
       while (p < header->chksum)
               chksum += *p++;
       chksum += sizeof(header->chksum) * ' ';
       p += sizeof(header->chksum);
       while (p < (const char *)header + sizeof(struct ustar_header))
               chksum += *p++;
       return chksum;
}

Can someone please look into this and possibly redirect if needed?

Thanks, Brendan