LZMS compression: use position instead of pointer for delta hash

This gives predictable results regardless of how the buffer is aligned.

diff --git a/src/lzms_compress.c b/src/lzms_compress.c
index 8db49668d296bf8d0340235ae78a4bc78aa372cf..88f39b300a9a16458451de80b5bf8729284c2f76 100644 (file)
--- a/src/lzms_compress.c
+++ b/src/lzms_compress.c
@@ -1202,7 +1202,7 @@ lzms_init_delta_matchfinder(struct lzms_compressor *c)
  * delta context with the specified @span.
  */
 static inline u32
-lzms_delta_hash(const u8 *p, u32 span)
+lzms_delta_hash(const u8 *p, const u32 pos, u32 span)
 {
        /* A delta match has a certain span and an offset that is a multiple of
         * that span.  To reduce wasted space we use a single combined hash
@@ -1214,7 +1214,7 @@ lzms_delta_hash(const u8 *p, u32 span)
        u8 d0 = *(p + 0) - *(p + 0 - span);
        u8 d1 = *(p + 1) - *(p + 1 - span);
        u8 d2 = *(p + 2) - *(p + 2 - span);
-       u32 v = ((span + ((u32)(uintptr_t)p & (span - 1))) << 24) |
+       u32 v = ((span + (pos & (span - 1))) << 24) |
                ((u32)d2 << 16) | ((u32)d1 << 8) | d0;
        return lz_hash(v, DELTA_HASH_ORDER);
 }
@@ -1250,7 +1250,7 @@ lzms_delta_matchfinder_skip_bytes(struct lzms_compressor *c,
                        const u32 span = (u32)1 << power;
                        if (unlikely(pos < span))
                                continue;
-                       const u32 next_hash = lzms_delta_hash(in_next + 1, span);
+                       const u32 next_hash = lzms_delta_hash(in_next + 1, pos + 1, span);
                        const u32 hash = c->next_delta_hashes[power];
                        c->delta_hash_table[hash] =
                                (power << DELTA_SOURCE_POWER_SHIFT) | pos;
@@ -1727,7 +1727,7 @@ begin:
                                if (unlikely(pos < span))
                                        continue;
 
-                               const u32 next_hash = lzms_delta_hash(in_next + 1, span);
+                               const u32 next_hash = lzms_delta_hash(in_next + 1, pos + 1, span);
                                const u32 hash = c->next_delta_hashes[power];
                                const u32 cur_match = c->delta_hash_table[hash];