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tar,smemcap: commonalyze checksumming code for tar header

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function                                             old     new   delta
chksum_and_xwrite_tar_header                           -      99     +99
writeheader                                          280     199     -81
chksum_and_xwrite                                    102       -    -102
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(add/remove: 2/1 grow/shrink: 0/1 up/down: 99/-183)           Total: -84 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Denys Vlasenko
2021-08-20 17:58:49 +02:00
parent 38e9c8c95b
commit 62d5a1e56f
4 changed files with 39 additions and 44 deletions
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35
archival/chksum_and_xwrite_tar_header.c Normal file
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/*
* Copyright (C) 2021 Denys Vlasenko <vda.linux@googlemail.com>
*
* Licensed under GPLv2, see file LICENSE in this source tree.
*/
//kbuild:lib-$(CONFIG_FEATURE_TAR_CREATE) += chksum_and_xwrite_tar_header.o
//kbuild:lib-$(CONFIG_SMEMCAP) += chksum_and_xwrite_tar_header.o
#include "libbb.h"
#include "bb_archive.h"
void FAST_FUNC chksum_and_xwrite_tar_header(int fd, struct tar_header_t *hp)
{
/* POSIX says that checksum is done on unsigned bytes
* (Sun and HP-UX gets it wrong... more details in
* GNU tar source) */
const unsigned char *cp;
int chksum, size;
strcpy(hp->magic, "ustar ");
/* Calculate and store the checksum (the sum of all of the bytes of
* the header). The checksum field must be filled with blanks for the
* calculation. The checksum field is formatted differently from the
* other fields: it has 6 digits, a NUL, then a space -- rather than
* digits, followed by a NUL like the other fields... */
memset(hp->chksum, ' ', sizeof(hp->chksum));
cp = (const unsigned char *) hp;
chksum = 0;
size = sizeof(*hp);
do { chksum += *cp++; } while (--size);
sprintf(hp->chksum, "%06o", chksum);
xwrite(fd, hp, sizeof(*hp));
}