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>

diff --git a/lib/Kconfig b/lib/Kconfig
index 6d7ce4b138c4308063285e39a5ba660e51ae7188..43359bb1ca9087510a13e04f052082c45ade967e 100644 (file)
--- 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 6fd191732feccde28220497240050f7b20ef72de..64cba2c3c7008fa1341cc28129c2c0796b935d25 100644 (file)
--- 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.