From: Eric Biggers <ebiggers3@gmail.com>
Date: Wed, 22 Jun 2016 01:01:57 +0000 (-0500)
Subject: lz_extend: simplify lz_extend() slightly
X-Git-Tag: v1.10.0~40
X-Git-Url: https://wimlib.net/git/?p=wimlib;a=commitdiff_plain;h=0ec3ead8ebd29703e12342c56b282ae37b188e6d;hp=76689b1cac26c545260568997ae7fb949846f302

lz_extend: simplify lz_extend() slightly

Unrolling the first four word copies does not seem give noticably better
performance anymore, and on a recent Intel processor actually appears to
decrease the performance slightly.
---

diff --git a/include/wimlib/lz_extend.h b/include/wimlib/lz_extend.h
index 858cb9a3..2fb76bc9 100644
--- a/include/wimlib/lz_extend.h
+++ b/include/wimlib/lz_extend.h
@@ -3,7 +3,7 @@
  *
  * The following copying information applies to this specific source code file:
  *
- * Written in 2014-2015 by Eric Biggers <ebiggers3@gmail.com>
+ * Written in 2014-2016 by Eric Biggers <ebiggers3@gmail.com>
  *
  * To the extent possible under law, the author(s) have dedicated all copyright
  * and related and neighboring rights to this software to the public domain
@@ -24,52 +24,30 @@
 #include "wimlib/bitops.h"
 #include "wimlib/unaligned.h"
 
-/* Return the number of bytes at @matchptr that match the bytes at @strptr, up
- * to a maximum of @max_len.  Initially, @start_len bytes are matched.  */
+/*
+ * Return the number of bytes at @matchptr that match the bytes at @strptr, up
+ * to a maximum of @max_len.  Initially, @len bytes are matched.
+ */
 static inline u32
 lz_extend(const u8 * const strptr, const u8 * const matchptr,
-	  const u32 start_len, const u32 max_len)
+	  u32 len, const u32 max_len)
 {
-	u32 len = start_len;
-	machine_word_t v_word;
-
-	if (UNALIGNED_ACCESS_IS_FAST) {
-
-		if (likely(max_len - len >= 4 * WORDSIZE)) {
-
-		#define COMPARE_WORD_STEP					\
-			v_word = load_word_unaligned(&matchptr[len]) ^		\
-				 load_word_unaligned(&strptr[len]);		\
-			if (v_word != 0)					\
-				goto word_differs;				\
-			len += WORDSIZE;					\
-
-			COMPARE_WORD_STEP
-			COMPARE_WORD_STEP
-			COMPARE_WORD_STEP
-			COMPARE_WORD_STEP
-		#undef COMPARE_WORD_STEP
-		}
-
-		while (len + WORDSIZE <= max_len) {
-			v_word = load_word_unaligned(&matchptr[len]) ^
-				 load_word_unaligned(&strptr[len]);
-			if (v_word != 0)
-				goto word_differs;
-			len += WORDSIZE;
+	while (UNALIGNED_ACCESS_IS_FAST && len + WORDSIZE <= max_len) {
+		machine_word_t v = load_word_unaligned(matchptr + len) ^
+				   load_word_unaligned(strptr + len);
+		if (v != 0) {
+			if (CPU_IS_LITTLE_ENDIAN)
+				len += ffsw(v) >> 3;
+			else
+				len += (8 * WORDSIZE - 1 - flsw(v)) >> 3;
+			return len;
 		}
+		len += WORDSIZE;
 	}
 
 	while (len < max_len && matchptr[len] == strptr[len])
 		len++;
 	return len;
-
-word_differs:
-	if (CPU_IS_LITTLE_ENDIAN)
-		len += (ffsw(v_word) >> 3);
-	else
-		len += (8 * WORDSIZE - 1 - flsw(v_word)) >> 3;
-	return len;
 }
 
 #endif /* _WIMLIB_LZ_EXTEND_H */