linux-ext4 - [PATCH 14/14] crc32: Select an algorithm via kconfig

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Message-ID: <20111201201517.5876.39207.stgit@elm3c44.beaverton.ibm.com>
Date:	Thu, 01 Dec 2011 12:15:17 -0800
From:	"Darrick J. Wong" <djwong@...ibm.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Theodore Tso <tytso@....edu>,
	Joakim Tjernlund <joakim.tjernlund@...nsmode.se>,
	Bob Pearson <rpearson@...temfabricworks.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Andreas Dilger <adilger.kernel@...ger.ca>,
	linux-crypto <linux-crypto@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Mingming Cao <cmm@...ibm.com>, linux-ext4@...r.kernel.org,
	Herbert Xu <herbert@...dor.apana.org.au>
Subject: [PATCH 14/14] crc32: Select an algorithm via kconfig

Allow the kernel builder to choose a crc32* algorithm for the kernel.

Signed-off-by: Darrick J. Wong <djwong@...ibm.com>
---
 lib/Kconfig     |   36 ++++++++++++++++++++++++++++++++++++
 lib/crc32defs.h |   18 ++++++++++++++++++
 2 files changed, 54 insertions(+), 0 deletions(-)


diff --git a/lib/Kconfig b/lib/Kconfig
index cfddafc..e9b9134 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -70,6 +70,42 @@ config CRC32_SELFTEST
 	  and crc32_be over byte strings with random alignment and length
 	  and computes the total elapsed time and number of bytes processed.
 
+choice
+	prompt "CRC32 implementation"
+	depends on CRC32
+	default CRC32_SLICEBY8
+
+config CRC32_SLICEBY8
+	bool "Slice by 8 bytes"
+	help
+	  Calculate checksum 8 bytes at a time with a clever slicing algorithm.
+	  This is the fastest algorithm, but comes with a 8KiB lookup table.
+	  Most modern processors have enough cache that this shouldn't be
+	  a problem.
+
+	  If you don't know which to choose, choose this one.
+
+config CRC32_SLICEBY4
+	bool "Slice by 4 bytes"
+	help
+	  Calculate checksum 4 bytes at a time with a clever slicing algorithm.
+	  This is a bit slower than slice by 8, but has a smaller 4KiB lookup
+	  table.
+
+config CRC32_SARWATE
+	bool "Sarwate's Algorithm (one byte at a time)"
+	help
+	  Calculate checksum a byte at a time using Sarwate's algorithm.  This
+	  is not particularly fast, but has a small 256 byte lookup table.
+
+config CRC32_BIT
+	bool "Classic Algorithm (one bit at a time)"
+	help
+	  Calculate checksum one bit at a time.  This is VERY slow, but has
+	  no lookup table.  This is provided as a debugging option.
+
+endchoice
+
 config CRC7
 	tristate "CRC7 functions"
 	help
diff --git a/lib/crc32defs.h b/lib/crc32defs.h
index 6fd1917..64cba2c 100644
--- a/lib/crc32defs.h
+++ b/lib/crc32defs.h
@@ -13,6 +13,24 @@
  */
 #define CRC32C_POLY_LE 0x82F63B78
 
+/* Try to choose an implementation variant via Kconfig */
+#ifdef CONFIG_CRC32_SLICEBY8
+# define CRC_LE_BITS 64
+# define CRC_BE_BITS 64
+#endif
+#ifdef CONFIG_CRC32_SLICEBY4
+# define CRC_LE_BITS 32
+# define CRC_BE_BITS 32
+#endif
+#ifdef CONFIG_CRC32_SARWATE
+# define CRC_LE_BITS 8
+# define CRC_BE_BITS 8
+#endif
+#ifdef CONFIG_CRC32_BIT
+# define CRC_LE_BITS 1
+# define CRC_BE_BITS 1
+#endif
+
 /*
  * How many bits at a time to use.  Valid values are 1, 2, 4, 8, 32 and 64.
  * For less performance-sensitive, use 4 or 8 to save table size.

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