Merge branch 'crc32'

Daniel Borkmann says:

====================
crc32 combine improvements

So almost a month passed, and I don't want this to get lost
somewhere. I have applied the feedback given at that time to
this set, rebased plus tested it against latest net-next. I
decided to route this via netdev as it improves performance
upon library code that provides library bits for SCTP, i.e.
for non-linear skb csum handling in IPVS. Thus, resending
this for George before it gets lost.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/crc32.h

@@ -8,8 +8,8 @@
 #include <linux/types.h>
 #include <linux/bitrev.h>
 
-extern u32  crc32_le(u32 crc, unsigned char const *p, size_t len);
-extern u32  crc32_be(u32 crc, unsigned char const *p, size_t len);
+u32 __pure crc32_le(u32 crc, unsigned char const *p, size_t len);
+u32 __pure crc32_be(u32 crc, unsigned char const *p, size_t len);
 
 /**
  * crc32_le_combine - Combine two crc32 check values into one. For two
@@ -29,9 +29,14 @@ extern u32  crc32_be(u32 crc, unsigned char const *p, size_t len);
  * 	   with the same initializer as crc1, and crc2 seed was 0. See
  * 	   also crc32_combine_test().
  */
-extern u32  crc32_le_combine(u32 crc1, u32 crc2, size_t len2);
+u32 __attribute_const__ crc32_le_shift(u32 crc, size_t len);
 
-extern u32  __crc32c_le(u32 crc, unsigned char const *p, size_t len);
+static inline u32 crc32_le_combine(u32 crc1, u32 crc2, size_t len2)
+{
+	return crc32_le_shift(crc1, len2) ^ crc2;
+}
+
+u32 __pure __crc32c_le(u32 crc, unsigned char const *p, size_t len);
 
 /**
  * __crc32c_le_combine - Combine two crc32c check values into one. For two
@@ -51,7 +56,12 @@ extern u32  __crc32c_le(u32 crc, unsigned char const *p, size_t len);
  * 	   seeded with the same initializer as crc1, and crc2 seed
  * 	   was 0. See also crc32c_combine_test().
  */
-extern u32  __crc32c_le_combine(u32 crc1, u32 crc2, size_t len2);
+u32 __attribute_const__ __crc32c_le_shift(u32 crc, size_t len);
+
+static inline u32 __crc32c_le_combine(u32 crc1, u32 crc2, size_t len2)
+{
+	return __crc32c_le_shift(crc1, len2) ^ crc2;
+}
 
 #define crc32(seed, data, length)  crc32_le(seed, (unsigned char const *)(data), length)
 

lib/crc32.c

@@ -50,34 +50,10 @@ MODULE_AUTHOR("Matt Domsch <Matt_Domsch@dell.com>");
 MODULE_DESCRIPTION("Various CRC32 calculations");
 MODULE_LICENSE("GPL");
 
-#define GF2_DIM		32
-
-static u32 gf2_matrix_times(u32 *mat, u32 vec)
-{
-	u32 sum = 0;
-
-	while (vec) {
-		if (vec & 1)
-			sum ^= *mat;
-		vec >>= 1;
-		mat++;
-	}
-
-	return sum;
-}
-
-static void gf2_matrix_square(u32 *square, u32 *mat)
-{
-	int i;
-
-	for (i = 0; i < GF2_DIM; i++)
-		square[i] = gf2_matrix_times(mat, mat[i]);
-}
-
 #if CRC_LE_BITS > 8 || CRC_BE_BITS > 8
 
 /* implements slicing-by-4 or slicing-by-8 algorithm */
-static inline u32
+static inline u32 __pure
 crc32_body(u32 crc, unsigned char const *buf, size_t len, const u32 (*tab)[256])
 {
 # ifdef __LITTLE_ENDIAN
@@ -155,51 +131,6 @@ crc32_body(u32 crc, unsigned char const *buf, size_t len, const u32 (*tab)[256])
 }
 #endif
 
-/* For conditions of distribution and use, see copyright notice in zlib.h */
-static u32 crc32_generic_combine(u32 crc1, u32 crc2, size_t len2,
-				 u32 polynomial)
-{
-	u32 even[GF2_DIM]; /* Even-power-of-two zeros operator */
-	u32 odd[GF2_DIM];  /* Odd-power-of-two zeros operator  */
-	u32 row;
-	int i;
-
-	if (len2 <= 0)
-		return crc1;
-
-	/* Put operator for one zero bit in odd */
-	odd[0] = polynomial;
-	row = 1;
-	for (i = 1; i < GF2_DIM; i++) {
-		odd[i] = row;
-		row <<= 1;
-	}
-
-	gf2_matrix_square(even, odd); /* Put operator for two zero bits in even */
-	gf2_matrix_square(odd, even); /* Put operator for four zero bits in odd */
-
-	/* Apply len2 zeros to crc1 (first square will put the operator for one
-	 * zero byte, eight zero bits, in even).
-	 */
-	do {
-		/* Apply zeros operator for this bit of len2 */
-		gf2_matrix_square(even, odd);
-		if (len2 & 1)
-			crc1 = gf2_matrix_times(even, crc1);
-		len2 >>= 1;
-		/* If no more bits set, then done */
-		if (len2 == 0)
-			break;
-		/* Another iteration of the loop with odd and even swapped */
-		gf2_matrix_square(odd, even);
-		if (len2 & 1)
-			crc1 = gf2_matrix_times(odd, crc1);
-		len2 >>= 1;
-	} while (len2 != 0);
-
-	crc1 ^= crc2;
-	return crc1;
-}
 
 /**
  * crc32_le_generic() - Calculate bitwise little-endian Ethernet AUTODIN II
@@ -271,19 +202,81 @@ u32 __pure __crc32c_le(u32 crc, unsigned char const *p, size_t len)
 			(const u32 (*)[256])crc32ctable_le, CRC32C_POLY_LE);
 }
 #endif
-u32 __pure crc32_le_combine(u32 crc1, u32 crc2, size_t len2)
+EXPORT_SYMBOL(crc32_le);
+EXPORT_SYMBOL(__crc32c_le);
+
+/*
+ * This multiplies the polynomials x and y modulo the given modulus.
+ * This follows the "little-endian" CRC convention that the lsbit
+ * represents the highest power of x, and the msbit represents x^0.
+ */
+static u32 __attribute_const__ gf2_multiply(u32 x, u32 y, u32 modulus)
 {
-	return crc32_generic_combine(crc1, crc2, len2, CRCPOLY_LE);
+	u32 product = x & 1 ? y : 0;
+	int i;
+
+	for (i = 0; i < 31; i++) {
+		product = (product >> 1) ^ (product & 1 ? modulus : 0);
+		x >>= 1;
+		product ^= x & 1 ? y : 0;
+	}
+
+	return product;
 }
 
-u32 __pure __crc32c_le_combine(u32 crc1, u32 crc2, size_t len2)
+/**
+ * crc32_generic_shift - Append len 0 bytes to crc, in logarithmic time
+ * @crc: The original little-endian CRC (i.e. lsbit is x^31 coefficient)
+ * @len: The number of bytes. @crc is multiplied by x^(8*@len)
+ * @polynomial: The modulus used to reduce the result to 32 bits.
+ *
+ * It's possible to parallelize CRC computations by computing a CRC
+ * over separate ranges of a buffer, then summing them.
+ * This shifts the given CRC by 8*len bits (i.e. produces the same effect
+ * as appending len bytes of zero to the data), in time proportional
+ * to log(len).
+ */
+static u32 __attribute_const__ crc32_generic_shift(u32 crc, size_t len,
+						   u32 polynomial)
 {
-	return crc32_generic_combine(crc1, crc2, len2, CRC32C_POLY_LE);
+	u32 power = polynomial;	/* CRC of x^32 */
+	int i;
+
+	/* Shift up to 32 bits in the simple linear way */
+	for (i = 0; i < 8 * (int)(len & 3); i++)
+		crc = (crc >> 1) ^ (crc & 1 ? polynomial : 0);
+
+	len >>= 2;
+	if (!len)
+		return crc;
+
+	for (;;) {
+		/* "power" is x^(2^i), modulo the polynomial */
+		if (len & 1)
+			crc = gf2_multiply(crc, power, polynomial);
+
+		len >>= 1;
+		if (!len)
+			break;
+
+		/* Square power, advancing to x^(2^(i+1)) */
+		power = gf2_multiply(power, power, polynomial);
+	}
+
+	return crc;
 }
-EXPORT_SYMBOL(crc32_le);
-EXPORT_SYMBOL(crc32_le_combine);
-EXPORT_SYMBOL(__crc32c_le);
-EXPORT_SYMBOL(__crc32c_le_combine);
+
+u32 __attribute_const__ crc32_le_shift(u32 crc, size_t len)
+{
+	return crc32_generic_shift(crc, len, CRCPOLY_LE);
+}
+
+u32 __attribute_const__ __crc32c_le_shift(u32 crc, size_t len)
+{
+	return crc32_generic_shift(crc, len, CRC32C_POLY_LE);
+}
+EXPORT_SYMBOL(crc32_le_shift);
+EXPORT_SYMBOL(__crc32c_le_shift);
 
 /**
  * crc32_be_generic() - Calculate bitwise big-endian Ethernet AUTODIN II CRC32
@@ -351,7 +344,7 @@ EXPORT_SYMBOL(crc32_be);
 #ifdef CONFIG_CRC32_SELFTEST
 
 /* 4096 random bytes */
-static u8 __attribute__((__aligned__(8))) test_buf[] =
+static u8 const __aligned(8) test_buf[] __initconst =
 {
 	0x5b, 0x85, 0x21, 0xcb, 0x09, 0x68, 0x7d, 0x30,
 	0xc7, 0x69, 0xd7, 0x30, 0x92, 0xde, 0x59, 0xe4,
@@ -875,7 +868,7 @@ static struct crc_test {
 	u32 crc_le;	/* expected crc32_le result */
 	u32 crc_be;	/* expected crc32_be result */
 	u32 crc32c_le;	/* expected crc32c_le result */
-} test[] =
+} const test[] __initconst =
 {
 	{0x674bf11d, 0x00000038, 0x00000542, 0x0af6d466, 0xd8b6e4c1, 0xf6e93d6c},
 	{0x35c672c6, 0x0000003a, 0x000001aa, 0xc6d3dfba, 0x28aaf3ad, 0x0fe92aca},