lzx-compress.c: Honor cache_limit

This ensures the match cache is never overrun.  If for some reason we
average more than LZX_CACHE_PER_POS (currently 8) matches per position,
_excluding skipped positions_, just don't return any more matches.

diff --git a/src/lzx-compress.c b/src/lzx-compress.c
index e65b6c8329e35faa4c1b72f5bd69a86b25e77e87..c8f61099f0f92c98b9ec9ea47790fc3523eabc58 100644 (file)
--- a/src/lzx-compress.c
+++ b/src/lzx-compress.c
@@ -251,12 +251,10 @@
 
 #define LZX_DIV_BLOCK_SIZE     32768
 
-#define LZX_CACHE_PER_POS      10
+#define LZX_CACHE_PER_POS      8
 
 #define LZX_CACHE_LEN (LZX_DIV_BLOCK_SIZE * (LZX_CACHE_PER_POS + 1))
 #define LZX_CACHE_SIZE (LZX_CACHE_LEN * sizeof(struct raw_match))
-
-/* Dependent on behavior of lz_bt_get_matches().  */
 #define LZX_MAX_MATCHES_PER_POS (LZX_MAX_MATCH_LEN - LZX_MIN_MATCH_LEN + 1)
 
 /* Codewords for the LZX main, length, and aligned offset Huffman codes  */
@@ -1260,11 +1258,15 @@ lzx_get_matches(struct lzx_compressor *ctx,
 
        cache_ptr = ctx->cache_ptr;
        matches = cache_ptr + 1;
-       if (ctx->matches_cached) {
-               num_matches = cache_ptr->len;
+       if (likely(cache_ptr <= ctx->cache_limit)) {
+               if (ctx->matches_cached) {
+                       num_matches = cache_ptr->len;
+               } else {
+                       num_matches = lz_bt_get_matches(&ctx->mf, matches);
+                       cache_ptr->len = num_matches;
+               }
        } else {
-               num_matches = lz_bt_get_matches(&ctx->mf, matches);
-               cache_ptr->len = num_matches;
+               num_matches = 0;
        }
 
        /* Don't allow matches to span the end of an LZX block.  */
@@ -1329,11 +1331,11 @@ lzx_skip_bytes(struct lzx_compressor *ctx, unsigned n)
        cache_ptr = ctx->cache_ptr;
        ctx->match_window_pos += n;
        if (ctx->matches_cached) {
-               while (n--)
+               while (n-- && cache_ptr <= ctx->cache_limit)
                        cache_ptr += 1 + cache_ptr->len;
        } else {
                lz_bt_skip_positions(&ctx->mf, n);
-               while (n--) {
+               while (n-- && cache_ptr <= ctx->cache_limit) {
                        cache_ptr->len = 0;
                        cache_ptr += 1;
                }