*: simplify checks for gz/bz2/xz magic

function                                             old     new   delta
send_tree                                            360     355      -5
rpm2cpio_main                                        249     220     -29
setup_unzip_on_fd                                    150     118     -32
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 0/3 up/down: 0/-66)             Total: -66 bytes

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

1 files changed, 12 insertions, 7 deletions

diff --git a/archival/rpm2cpio.c b/archival/rpm2cpio.c
index 598ec8670..1c67dcc6e 100644
--- a/archival/rpm2cpio.c
+++ b/archival/rpm2cpio.c
@@ -68,26 +68,31 @@ int rpm2cpio_main(int argc UNUSED_PARAM, char **argv)
 #else
         /* BLOAT */
         {
-                unsigned char magic[8];
+                union {
+                        uint8_t b[4];
+                        uint16_t b16[2];
+                        uint32_t b32[1];
+                } magic;
                 IF_DESKTOP(long long) int FAST_FUNC (*unpack)(int src_fd, int dst_fd);
 
-                xread(rpm_fd, &magic, 2);
-                if (magic[0] == 0x1f && magic[1] == 0x8b) {
+                xread(rpm_fd, magic.b16, sizeof(magic.b16));
+                if (magic.b16[0] == GZIP_MAGIC) {
                         unpack = unpack_gz_stream;
                 } else
                 if (ENABLE_FEATURE_SEAMLESS_BZ2
-                 && magic[0] == 'B' && magic[1] == 'Z'
+                 && magic.b16[0] == BZIP2_MAGIC
                 ) {
                         unpack = unpack_bz2_stream;
                 } else
                 if (ENABLE_FEATURE_SEAMLESS_XZ
-                 && magic[0] == 0xfd && magic[1] == '7'
+                 && magic.b16[0] == XZ_MAGIC1
                 ) {
                         /* .xz signature: 0xfd, '7', 'z', 'X', 'Z', 0x00 */
                         /* More info at: http://tukaani.org/xz/xz-file-format.txt */
-                        xread(rpm_fd, magic + 2, 4);
-                        if (strcmp((char*)magic + 2, "zXZ") != 0)
+                        xread(rpm_fd, magic.b32, sizeof(magic.b32));
+                        if (magic.b32[0] != XZ_MAGIC2)
                                 goto no_magic;
+                        /* unpack_xz_stream wants fd at position 0 */
                         xlseek(rpm_fd, -6, SEEK_CUR);
                         unpack = unpack_xz_stream;
                 } else {