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authorDarrick J. Wong <djwong@us.ibm.com>2012-03-23 15:02:26 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2012-03-23 16:58:38 -0700
commit5cde7656d0dd222170eb0250bd1f70c9018fd438 (patch)
tree6ebd5b76968f84d5fd8545cfe3400162d76d222c
parent577eba9e22e872574c466648b46eeb3e0d04372e (diff)
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@us.ibm.com> Cc: Bob Pearson <rpearson@systemfabricworks.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--lib/Kconfig43
-rw-r--r--lib/crc32defs.h18
2 files changed, 61 insertions, 0 deletions
diff --git a/lib/Kconfig b/lib/Kconfig
index 6d7ce4b138c4..43359bb1ca90 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -80,6 +80,49 @@ 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 to hold this table without
+ thrashing the cache.
+
+ This is the default implementation choice. Choose this one unless
+ you have a good reason not to.
+
+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.
+
+ Only choose this option if you know what you are doing.
+
+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.
+
+ Only choose this option if you know what you are doing.
+
+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.
+
+ Only choose this option if you are debugging crc32.
+
+endchoice
+
config CRC7
tristate "CRC7 functions"
help
diff --git a/lib/crc32defs.h b/lib/crc32defs.h
index 6fd191732fec..64cba2c3c700 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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