2 files changed, 82 insertions, 79 deletions

diff --git a/include/linux/crc32.h b/include/linux/crc32.h
index 7d275c4fc011..edf34e876e40 100644
--- a/include/linux/crc32.h
+++ b/include/linux/crc32.h
@@ -29,7 +29,12 @@ 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);
+
+static inline u32 crc32_le_combine(u32 crc1, u32 crc2, size_t len2)
+{
+        return crc32_le_shift(crc1, len2) ^ crc2;
+}
 
 extern u32  __crc32c_le(u32 crc, unsigned char const *p, size_t len);
 
@@ -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)
 
diff --git a/lib/crc32.c b/lib/crc32.c
index 21a7b2135af6..9af30ff334c5 100644
--- a/lib/crc32.c
+++ b/lib/crc32.c
@@ -50,30 +50,6 @@ 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 */
@@ -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