From: Michihiro NAKAJIMA <ggcueroad@gmail.com>
Date: Mon, 15 Aug 2011 02:03:10 +0000 (-0400)
Subject: Improve crc32 in archive_crc32.h for its performance.
X-Git-Tag: v3.0.0a~138
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=8ecd7359d3f04be8e421d096b3a9b2b7ee05f2d8;p=thirdparty%2Flibarchive.git

Improve crc32 in archive_crc32.h for its performance.
A use of expansion code can make crc32 fast about 20% -30%
in any gcc optimization option(-O0,-O1,-O2 and -O3).

SVN-Revision: 3604
---

diff --git a/libarchive/archive_crc32.h b/libarchive/archive_crc32.h
index 103e5df35..cd633af89 100644
--- a/libarchive/archive_crc32.h
+++ b/libarchive/archive_crc32.h
@@ -60,6 +60,18 @@ crc32(unsigned long crc, const void *_p, size_t len)
 	}
 
 	crc = crc ^ 0xffffffffUL;
+	/* A use of this loop is about 20% - 30% faster than
+	 * no use version in any optimization option of gcc.  */
+	for (;len >= 8; len -= 8) {
+		crc = crc_tbl[(crc ^ *p++) & 0xff] ^ (crc >> 8);
+		crc = crc_tbl[(crc ^ *p++) & 0xff] ^ (crc >> 8);
+		crc = crc_tbl[(crc ^ *p++) & 0xff] ^ (crc >> 8);
+		crc = crc_tbl[(crc ^ *p++) & 0xff] ^ (crc >> 8);
+		crc = crc_tbl[(crc ^ *p++) & 0xff] ^ (crc >> 8);
+		crc = crc_tbl[(crc ^ *p++) & 0xff] ^ (crc >> 8);
+		crc = crc_tbl[(crc ^ *p++) & 0xff] ^ (crc >> 8);
+		crc = crc_tbl[(crc ^ *p++) & 0xff] ^ (crc >> 8);
+	}
 	while (len--)
 		crc = crc_tbl[(crc ^ *p++) & 0xff] ^ (crc >> 8);
 	return (crc ^ 0xffffffffUL);