X-Git-Url: https://wimlib.net/git/?a=blobdiff_plain;f=include%2Fwimlib%2Flz_hash.h;h=5aa4eff5d34319677f1a42e4bca6bf6ff132fd6d;hb=acb5c41d2c9be655eca863a0315a22d1f54889e2;hp=9d097ae668e0ec1b0b1baffae76c976125f3d17e;hpb=e940fda88a92ff9e931ec88fb4c0e1ebd6fa2dfb;p=wimlib

diff --git a/include/wimlib/lz_hash.h b/include/wimlib/lz_hash.h
index 9d097ae6..5aa4eff5 100644
--- a/include/wimlib/lz_hash.h
+++ b/include/wimlib/lz_hash.h
@@ -1,30 +1,60 @@
-#ifndef _WIMLIB_LZ_HASH_H
-#define _WIMLIB_LZ_HASH_H
+/*
+ * lz_hash.h
+ *
+ * Hashing for Lempel-Ziv matchfinding.
+ *
+ * Author:	Eric Biggers
+ * Year:	2014, 2015
+ *
+ * The author dedicates this file to the public domain.
+ * You can do whatever you want with this file.
+ */
 
-#include "wimlib/compress_common.h"
+#ifndef _LZ_HASH_H
+#define _LZ_HASH_H
 
-struct lz_params {
-	unsigned min_match;
-	unsigned max_match;
-	unsigned max_offset;
-	unsigned nice_match;
-	unsigned good_match;
-	unsigned max_chain_len;
-	unsigned max_lazy_match;
-	unsigned too_far;
-};
+#include "wimlib/unaligned.h"
 
-typedef void (*lz_record_match_t)(unsigned len, unsigned offset, void *ctx);
-typedef void (*lz_record_literal_t)(u8 lit, void *ctx);
+/*
+ * The hash function: given a sequence prefix held in the low-order bits of a
+ * 32-bit value, multiply by a carefully-chosen large constant.  Discard any
+ * bits of the product that don't fit in a 32-bit value, but take the
+ * next-highest @num_bits bits of the product as the hash value, as those have
+ * the most randomness.
+ */
+static inline u32
+lz_hash(u32 seq, unsigned num_bits)
+{
+	return (u32)(seq * 0x1E35A7BD) >> (32 - num_bits);
+}
 
-extern void
-lz_analyze_block(const u8 window[restrict],
-		 input_idx_t window_size,
-		 lz_record_match_t record_match,
-		 lz_record_literal_t record_literal,
-		 void *record_ctx,
-		 const struct lz_params *params,
-		 input_idx_t prev_tab[restrict]);
+/*
+ * Hash the 2-byte sequence beginning at @p, producing a hash of length
+ * @num_bits bits.  At least 2 bytes of data must be available at @p.
+ */
+static inline u32
+lz_hash_2_bytes(const u8 *p, unsigned num_bits)
+{
+	u32 seq = load_u16_unaligned(p);
+	if (num_bits >= 16)
+		return seq;
+	return lz_hash(seq, num_bits);
+}
 
+/*
+ * Hash the 3-byte sequence beginning at @p, producing a hash of length
+ * @num_bits bits.  At least LZ_HASH3_REQUIRED_NBYTES bytes of data must be
+ * available at @p; note that this may be more than 3.
+ */
+static inline u32
+lz_hash_3_bytes(const u8 *p, unsigned num_bits)
+{
+	u32 seq = load_u24_unaligned(p);
+	if (num_bits >= 24)
+		return seq;
+	return lz_hash(seq, num_bits);
+}
 
-#endif /* _WIMLIB_LZ_HASH_H  */
+#define LZ_HASH3_REQUIRED_NBYTES LOAD_U24_REQUIRED_NBYTES
+
+#endif /* _LZ_HASH_H */