crc32: make CRC_*_BITS definition correspond to actual bit counts

crc32.c provides a choice of one of several algorithms for computing the
LSB and LSB versions of the CRC32 checksum based on the parameters
CRC_LE_BITS and CRC_BE_BITS.

In the original version the values 1, 2, 4 and 8 respectively selected
versions of the alrogithm that computed the crc 1, 2, 4 and 32 bits as a
time.

This patch series adds a new version that computes the CRC 64 bits at a
time.  To make things easier to understand the parameter has been
reinterpreted to actually stand for the number of bits processed in each
step of the algorithm so that the old value 8 has been replaced with the
value 32.

This also allows us to add in a widely used crc algorithm that computes
the crc 8 bits at a time called the Sarwate algorithm.

[[email protected]: Minor changelog tweaks]
Signed-off-by: Bob Pearson <[email protected]>
Signed-off-by: Darrick J. Wong <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

lib/crc32.c

@@ -27,13 +27,13 @@
 #include <linux/types.h>
 #include "crc32defs.h"
 
-#if CRC_LE_BITS == 8
+#if CRC_LE_BITS > 8
 # define tole(x) ((__force u32) __constant_cpu_to_le32(x))
 #else
 # define tole(x) (x)
 #endif
 
-#if CRC_BE_BITS == 8
+#if CRC_BE_BITS > 8
 # define tobe(x) ((__force u32) __constant_cpu_to_be32(x))
 #else
 # define tobe(x) (x)
@@ -45,7 +45,7 @@ MODULE_AUTHOR("Matt Domsch <[email protected]>");
 MODULE_DESCRIPTION("Ethernet CRC32 calculations");
 MODULE_LICENSE("GPL");
 
-#if CRC_LE_BITS == 8 || CRC_BE_BITS == 8
+#if CRC_LE_BITS > 8 || CRC_BE_BITS > 8
 
 static inline u32
 crc32_body(u32 crc, unsigned char const *buf, size_t len, const u32 (*tab)[256])
@@ -126,6 +126,12 @@ u32 __pure crc32_le(u32 crc, unsigned char const *p, size_t len)
 		crc = (crc >> 4) ^ crc32table_le[0][crc & 15];
 	}
 # elif CRC_LE_BITS == 8
+	/* aka Sarwate algorithm */
+	while (len--) {
+		crc ^= *p++;
+		crc = (crc >> 8) ^ crc32table_le[0][crc & 255];
+	}
+# else
 	const u32      (*tab)[] = crc32table_le;
 
 	crc = (__force u32) __cpu_to_le32(crc);
@@ -169,6 +175,11 @@ u32 __pure crc32_be(u32 crc, unsigned char const *p, size_t len)
 		crc = (crc << 4) ^ crc32table_be[0][crc >> 28];
 	}
 # elif CRC_BE_BITS == 8
+	while (len--) {
+		crc ^= *p++ << 24;
+		crc = (crc << 8) ^ crc32table_be[0][crc >> 24];
+	}
+# else
 	const u32      (*tab)[] = crc32table_be;
 
 	crc = (__force u32) __cpu_to_be32(crc);

lib/crc32defs.h

@@ -6,27 +6,29 @@
 #define CRCPOLY_LE 0xedb88320
 #define CRCPOLY_BE 0x04c11db7
 
-/* How many bits at a time to use.  Requires a table of 4<<CRC_xx_BITS bytes. */
-/* For less performance-sensitive, use 4 */
+/* How many bits at a time to use.  Valid values are 1, 2, 4, 8, and 32. */
+/* For less performance-sensitive, use 4 or 8 */
 #ifndef CRC_LE_BITS
-# define CRC_LE_BITS 8
+# define CRC_LE_BITS 32
 #endif
 #ifndef CRC_BE_BITS
-# define CRC_BE_BITS 8
+# define CRC_BE_BITS 32
 #endif
 
 /*
  * Little-endian CRC computation.  Used with serial bit streams sent
  * lsbit-first.  Be sure to use cpu_to_le32() to append the computed CRC.
  */
-#if CRC_LE_BITS > 8 || CRC_LE_BITS < 1 || CRC_LE_BITS & CRC_LE_BITS-1
-# error CRC_LE_BITS must be a power of 2 between 1 and 8
+#if CRC_LE_BITS > 32 || CRC_LE_BITS < 1 || CRC_LE_BITS == 16 || \
+	CRC_LE_BITS & CRC_LE_BITS-1
+# error "CRC_LE_BITS must be one of {1, 2, 4, 8, 32}"
 #endif
 
 /*
  * Big-endian CRC computation.  Used with serial bit streams sent
  * msbit-first.  Be sure to use cpu_to_be32() to append the computed CRC.
  */
-#if CRC_BE_BITS > 8 || CRC_BE_BITS < 1 || CRC_BE_BITS & CRC_BE_BITS-1
-# error CRC_BE_BITS must be a power of 2 between 1 and 8
+#if CRC_BE_BITS > 32 || CRC_BE_BITS < 1 || CRC_BE_BITS == 16 || \
+	CRC_BE_BITS & CRC_BE_BITS-1
+# error "CRC_BE_BITS must be one of {1, 2, 4, 8, 32}"
 #endif

lib/gen_crc32table.c

@@ -4,8 +4,17 @@
 
 #define ENTRIES_PER_LINE 4
 
+#if CRC_LE_BITS <= 8
 #define LE_TABLE_SIZE (1 << CRC_LE_BITS)
+#else
+#define LE_TABLE_SIZE 256
+#endif
+
+#if CRC_BE_BITS <= 8
 #define BE_TABLE_SIZE (1 << CRC_BE_BITS)
+#else
+#define BE_TABLE_SIZE 256
+#endif
 
 static uint32_t crc32table_le[4][256];
 static uint32_t crc32table_be[4][256];
@@ -24,7 +33,7 @@ static void crc32init_le(void)
 
 	crc32table_le[0][0] = 0;
 
-	for (i = 1 << (CRC_LE_BITS - 1); i; i >>= 1) {
+	for (i = LE_TABLE_SIZE >> 1; i; i >>= 1) {
 		crc = (crc >> 1) ^ ((crc & 1) ? CRCPOLY_LE : 0);
 		for (j = 0; j < LE_TABLE_SIZE; j += 2 * i)
 			crc32table_le[0][i + j] = crc ^ crc32table_le[0][j];