lzms-compress.c: Don't underrun window when checking recent offsets

In LZMS, not all recent offsets are initialized to 1, unlike in LZX.

diff --git a/include/wimlib/lzms.h b/include/wimlib/lzms.h
index 798b339c5fc63856586c971158a5e183355cee4a..76381a416829de89773d65de795d788cd7b06b7f 100644 (file)
--- a/include/wimlib/lzms.h
+++ b/include/wimlib/lzms.h
@@ -16,6 +16,7 @@
 #endif
 
 #define LZMS_NUM_RECENT_OFFSETS                        3
+#define LZMS_MAX_INIT_RECENT_OFFSET            (LZMS_NUM_RECENT_OFFSETS + 1)
 
 #define LZMS_PROBABILITY_BITS                  6
 #define LZMS_PROBABILITY_MAX                   (1U << LZMS_PROBABILITY_BITS)

diff --git a/src/lzms-compress.c b/src/lzms-compress.c
index a4d45300681f6871f14fcbec0886fb67cf9b3a6b..c6592a9f605598e02a25fd306570333decf23d88 100644 (file)
--- a/src/lzms-compress.c
+++ b/src/lzms-compress.c
@@ -888,7 +888,7 @@ lzms_get_near_optimal_match(struct lzms_compressor *ctx)
        ctx->optimum_end_idx = 0;
 
        longest_rep_len = ctx->params.min_match_length - 1;
-       if (lz_bt_get_position(&ctx->mf) >= 1) {
+       if (lz_bt_get_position(&ctx->mf) >= LZMS_MAX_INIT_RECENT_OFFSET) {
                u32 limit = min(ctx->params.max_match_length,
                                lz_bt_get_remaining_size(&ctx->mf));
                for (int i = 0; i < LZMS_NUM_RECENT_OFFSETS; i++) {
@@ -984,18 +984,20 @@ lzms_get_near_optimal_match(struct lzms_compressor *ctx)
                        return lzms_match_chooser_reverse_list(ctx, cur_pos);
 
                longest_rep_len = ctx->params.min_match_length - 1;
-               u32 limit = min(ctx->params.max_match_length,
-                               lz_bt_get_remaining_size(&ctx->mf));
-               for (int i = 0; i < LZMS_NUM_RECENT_OFFSETS; i++) {
-                       u32 offset = ctx->optimum[cur_pos].state.lru.recent_offsets[i];
-                       const u8 *strptr = lz_bt_get_window_ptr(&ctx->mf);
-                       const u8 *matchptr = strptr - offset;
-                       u32 len = 0;
-                       while (len < limit && strptr[len] == matchptr[len])
-                               len++;
-                       if (len > longest_rep_len) {
-                               longest_rep_len = len;
-                               longest_rep_offset = offset;
+               if (lz_bt_get_position(&ctx->mf) >= LZMS_MAX_INIT_RECENT_OFFSET) {
+                       u32 limit = min(ctx->params.max_match_length,
+                                       lz_bt_get_remaining_size(&ctx->mf));
+                       for (int i = 0; i < LZMS_NUM_RECENT_OFFSETS; i++) {
+                               u32 offset = ctx->optimum[cur_pos].state.lru.recent_offsets[i];
+                               const u8 *strptr = lz_bt_get_window_ptr(&ctx->mf);
+                               const u8 *matchptr = strptr - offset;
+                               u32 len = 0;
+                               while (len < limit && strptr[len] == matchptr[len])
+                                       len++;
+                               if (len > longest_rep_len) {
+                                       longest_rep_len = len;
+                                       longest_rep_offset = offset;
+                               }
                        }
                }