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authorDenys Vlasenko <vda.linux@googlemail.com>2017-01-09 14:28:25 +0100
committerDenys Vlasenko <vda.linux@googlemail.com>2017-01-09 14:28:25 +0100
commit590402bb55be940310f68d14a540f2d109420a98 (patch)
treecdc1a5516a1a5217faf4ad32b4f9c5d5886ef120 /archival/libarchive
parent3989e5adf454a3ab98412b249c2c9bd2a3175ae0 (diff)
downloadbusybox-590402bb55be940310f68d14a540f2d109420a98.tar.gz
unlzma: expand comments, no code changes
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
Diffstat (limited to 'archival/libarchive')
-rw-r--r--archival/libarchive/decompress_unlzma.c18
1 files changed, 18 insertions, 0 deletions
diff --git a/archival/libarchive/decompress_unlzma.c b/archival/libarchive/decompress_unlzma.c
index 90a428583..a9040877e 100644
--- a/archival/libarchive/decompress_unlzma.c
+++ b/archival/libarchive/decompress_unlzma.c
@@ -432,6 +432,21 @@ unpack_lzma_stream(transformer_state_t *xstate)
}
len += LZMA_MATCH_MIN_LEN;
+ /*
+ * LZMA SDK has this optimized:
+ * it precalculates size and copies many bytes
+ * in a loop with simpler checks, a-la:
+ * do
+ * *(dest) = *(dest + ofs);
+ * while (++dest != lim);
+ * and
+ * do {
+ * buffer[buffer_pos++] = buffer[pos];
+ * if (++pos == header.dict_size)
+ * pos = 0;
+ * } while (--cur_len != 0);
+ * Our code is slower (more checks per byte copy):
+ */
IF_NOT_FEATURE_LZMA_FAST(string:)
do {
uint32_t pos = buffer_pos - rep0;
@@ -451,6 +466,9 @@ unpack_lzma_stream(transformer_state_t *xstate)
} while (len != 0 && buffer_pos < header.dst_size);
/* FIXME: ...........^^^^^
* shouldn't it be "global_pos + buffer_pos < header.dst_size"?
+ * It probably should, but it is a "do we accidentally
+ * unpack more bytes than expected?" check - which
+ * never happens for well-formed compression data...
*/
}
}