tar: support GNU 256-bit encoding in all numeric fields

function                                             old     new   delta
getOctal                                              63     125     +62
get_header_tar                                      1572    1496     -76
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 1/1 up/down: 62/-76)            Total: -14 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 31 insertions, 80 deletions

diff --git a/archival/libunarchive/get_header_tar.c b/archival/libunarchive/get_header_tar.c
index adb4c157b..fcddcb834 100644
--- a/archival/libunarchive/get_header_tar.c
+++ b/archival/libunarchive/get_header_tar.c
@@ -18,87 +18,45 @@ typedef uint32_t aliased_uint32_t FIX_ALIASING;
 typedef off_t    aliased_off_t    FIX_ALIASING;
 
 
-/*
- * GNU tar uses "base-256 encoding" for very large numbers (>8 billion).
- * Encoding is binary, with highest bit always set as a marker
- * and sign in next-highest bit:
- * 80 00 .. 00 - zero
- * bf ff .. ff - largest positive number
- * ff ff .. ff - minus 1
- * c0 00 .. 00 - smallest negative number
- *
- * We expect it only in size field, where negative numbers don't make sense.
- */
-static off_t getBase256_len12(const char *str)
-{
-        off_t value;
-        int len;
-
-        /* if (*str & 0x40) error; - caller prevents this */
-
-        if (sizeof(off_t) >= 12) {
-                /* Probably 128-bit (16 byte) off_t. Can be optimized. */
-                len = 12;
-                value = *str++ & 0x3f;
-                while (--len)
-                        value = (value << 8) + (unsigned char) *str++;
-                return value;
-        }
-
-#ifdef CHECK_FOR_OVERFLOW
-        /* Can be optimized to eat 32-bit chunks */
-        char c = *str++ & 0x3f;
-        len = 12;
-        while (1) {
-                if (c)
-                        bb_error_msg_and_die("overflow in base-256 encoded file size");
-                if (--len == sizeof(off_t))
-                        break;
-                c = *str++;
-        }
-#else
-        str += (12 - sizeof(off_t));
-#endif
-
-/* Now str points to sizeof(off_t) least significant bytes.
- *
- * Example of tar file with 8914993153 (0x213600001) byte file.
- * Field starts at offset 7c:
- * 00070  30 30 30 00 30 30 30 30  30 30 30 00 80 00 00 00  |000.0000000.....|
- * 00080  00 00 00 02 13 60 00 01  31 31 31 32 30 33 33 36  |.....`..11120336|
- *
- * str is at offset 80 or 84 now (64-bit or 32-bit off_t).
- * We (ab)use the fact that value happens to be aligned,
- * and fetch it in one go:
- */
-        if (sizeof(off_t) == 8) {
-                value = *(aliased_off_t*)str;
-                value = SWAP_BE64(value);
-        } else if (sizeof(off_t) == 4) {
-                value = *(aliased_off_t*)str;
-                value = SWAP_BE32(value);
-        } else {
-                value = 0;
-                len = sizeof(off_t);
-                while (--len)
-                        value = (value << 8) + (unsigned char) *str++;
-        }
-        return value;
-}
-
 /* NB: _DESTROYS_ str[len] character! */
 static unsigned long long getOctal(char *str, int len)
 {
         unsigned long long v;
+        char *end;
         /* NB: leading spaces are allowed. Using strtoull to handle that.
          * The downside is that we accept e.g. "-123" too :(
          */
         str[len] = '\0';
-        v = strtoull(str, &str, 8);
+        v = strtoull(str, &end, 8);
         /* std: "Each numeric field is terminated by one or more
          * <space> or NUL characters". We must support ' '! */
-        if (*str != '\0' && *str != ' ')
-                bb_error_msg_and_die("corrupted octal value in tar header");
+        if (*end != '\0' && *end != ' ') {
+                int8_t first = str[0];
+                if (!(first & 0x80))
+                        bb_error_msg_and_die("corrupted octal value in tar header");
+                /*
+                 * GNU tar uses "base-256 encoding" for very large numbers.
+                 * Encoding is binary, with highest bit always set as a marker
+                 * and sign in next-highest bit:
+                 * 80 00 .. 00 - zero
+                 * bf ff .. ff - largest positive number
+                 * ff ff .. ff - minus 1
+                 * c0 00 .. 00 - smallest negative number
+                 *
+                 * Example of tar file with 8914993153 (0x213600001) byte file.
+                 * Field starts at offset 7c:
+                 * 00070  30 30 30 00 30 30 30 30  30 30 30 00 80 00 00 00  |000.0000000.....|
+                 * 00080  00 00 00 02 13 60 00 01  31 31 31 32 30 33 33 36  |.....`..11120336|
+                 *
+                 * NB: tarballs with NEGATIVE unix times encoded that way were seen!
+                 */
+                v = first;
+                /* Sign-extend using 6th bit: */
+                v <<= sizeof(unsigned long long)*8 - 7;
+                v = (long long)v >> (sizeof(unsigned long long)*8 - 7);
+                while (--len != 0)
+                        v = (v << 8) + (unsigned char) *str++;
+        }
         return v;
 }
 #define GET_OCTAL(a) getOctal((a), sizeof(a))
@@ -358,15 +316,8 @@ char FAST_FUNC get_header_tar(archive_handle_t *archive_handle)
         file_header->tar__uname = tar.uname[0] ? xstrndup(tar.uname, sizeof(tar.uname)) : NULL;
         file_header->tar__gname = tar.gname[0] ? xstrndup(tar.gname, sizeof(tar.gname)) : NULL;
 #endif
-        /* mtime: rudimentally handle GNU tar's "base256 encoding"
-         * People report tarballs with NEGATIVE unix times encoded that way */
-        file_header->mtime = (tar.mtime[0] & 0x80) /* base256? */
-                        ? 0 /* bogus */
-                        : GET_OCTAL(tar.mtime);
-        /* size: handle GNU tar's "base256 encoding" */
-        file_header->size = (tar.size[0] & 0xc0) == 0x80 /* positive base256? */
-                        ? getBase256_len12(tar.size)
-                        : GET_OCTAL(tar.size);
+        file_header->mtime = GET_OCTAL(tar.mtime);
+        file_header->size = GET_OCTAL(tar.size);
         file_header->gid = GET_OCTAL(tar.gid);
         file_header->uid = GET_OCTAL(tar.uid);
         /* Set bits 0-11 of the files mode */