dedup

commit d60ace395a74a5efe067ee9cd5d85446c7facf43
parent d8bfc3a69ce4c3c35dfa8c0d5cef3ce10e424300
Author: sin <sin@2f30.org>
Date:   Tue, 26 Feb 2019 09:48:57 +0000

When matching a pattern check if bottom bits of hash are 0

This approach is more efficient and easier to understand.

Diffstat:
M
chunker.c
 | 
10
+---------
M
config.h
 | 
1
+

2 files changed, 2 insertions(+), 9 deletions(-)
diff --git a/chunker.c b/chunker.c
@@ -14,7 +14,6 @@ struct chunker {
 	size_t cap;
 	size_t rpos;
 	size_t wpos;
-	size_t discr;
 	int fd;
 };
 
@@ -88,7 +87,7 @@ match_pattern(struct chunker *chunker, size_t chunk_size, uint32_t fp)
 		return 1;
 	if (chunk_size < BLKSIZE_MIN)
 		return 0;
-	return (fp % chunker->discr) == chunker->discr - 1;
+	return (fp & HASHMASK_BITS) == 0;
 }
 
 static size_t
@@ -123,12 +122,6 @@ get_chunk_size(struct chunker *chunker)
 	return chunk_size;
 }
 
-static size_t
-calc_discr(size_t avg)
-{
-	return avg / (-1.42888852e-7 * avg + 1.33237515);
-}
-
 struct chunker *
 alloc_chunker(size_t cap, int fd)
 {
@@ -145,7 +138,6 @@ alloc_chunker(size_t cap, int fd)
 	chunker->rpos = 0;
 	chunker->wpos = 0;
 	chunker->fd = fd;
-	chunker->discr = calc_discr(BLKSIZE_AVG);
 
 	return chunker;
 }
diff --git a/config.h b/config.h
@@ -1,4 +1,5 @@
 #define BLKSIZE_AVG ((size_t)524288)
 #define BLKSIZE_MIN ((BLKSIZE_AVG) / 4)
 #define BLKSIZE_MAX ((BLKSIZE_AVG) * 4)
+#define HASHMASK_BITS (BLKSIZE_AVG - 1)
 #define WINSIZE 32