[PATCHv2 3/7] lib: add rocksoft model crc64

[Keith Busch]

The NVM Express specification extended data integrity fields to 64 bits
using the Rocksoft^TM parameters. Add the poly to the crc64 table
generation, and provide a library routine implementing the algorithm.

The Rocksoft 64-bit CRC model parameters are as follows:
    Poly: 0xAD93D23594C93659
    Initial value: 0xFFFFFFFFFFFFFFFF
    Reflected Input: True
    Reflected Output: True
    Xor Final: 0xFFFFFFFFFFFFFFFF

Since this model used reflected bits, the implementation generates the
reflected table so the result is ordered consistently.

Cc: Eric Biggers <ebiggers at kernel.org>
Signed-off-by: Keith Busch <kbusch at kernel.org>
---
v1->v2:

  Generate a reflected table for the polynomial so that the inputs and
  outputs don't need to be reflected during calculating the CRC

 include/linux/crc64.h |  2 ++
 lib/crc64.c           | 26 ++++++++++++++++++++++
 lib/gen_crc64table.c  | 51 +++++++++++++++++++++++++++++++++----------
 3 files changed, 68 insertions(+), 11 deletions(-)

diff --git a/include/linux/crc64.h b/include/linux/crc64.h
index c756e65a1b58..9f2f20216503 100644
--- a/include/linux/crc64.h
+++ b/include/linux/crc64.h
@@ -8,4 +8,6 @@
 #include <linux/types.h>
 
 u64 __pure crc64_be(u64 crc, const void *p, size_t len);
+u64 __pure crc64_rocksoft(u64 crc, const void *p, size_t len);
+
 #endif /* _LINUX_CRC64_H */
diff --git a/lib/crc64.c b/lib/crc64.c
index 9f852a89ee2a..e223e72be44d 100644
--- a/lib/crc64.c
+++ b/lib/crc64.c
@@ -22,6 +22,13 @@
  * x^24 + x^23 + x^22 + x^21 + x^19 + x^17 + x^13 + x^12 + x^10 + x^9 +
  * x^7 + x^4 + x + 1
  *
+ * crc64rocksoft[256] table is from the Rocksoft specification polynomial
+ * defined as,
+ *
+ * x^64 + x^63 + x^61 + x^59 + x^58 + x^56 + x^55 + x^52 + x^49 + x^48 + x^47 +
+ * x^46 + x^44 + x^41 + x^37 + x^36 + x^34 + x^32 + x^31 + x^28 + x^26 + x^23 +
+ * x^22 + x^19 + x^16 + x^13 + x^12 + x^10 + x^9 + x^6 + x^4 + x^3 + 1
+ *
  * Copyright 2018 SUSE Linux.
  *   Author: Coly Li <colyli at suse.de>
  */
@@ -55,3 +62,22 @@ u64 __pure crc64_be(u64 crc, const void *p, size_t len)
 	return crc;
 }
 EXPORT_SYMBOL_GPL(crc64_be);
+
+/**
+ * crc64_rocksoft - Calculate bitwise Rocksoft CRC64
+ * @crc: seed value for computation. (u64)~0 for a new CRC calculation, or the
+ * 	 previous crc64 value if computing incrementally.
+ * @p: pointer to buffer over which CRC64 is run
+ * @len: length of buffer @p
+ */
+u64 __pure crc64_rocksoft(u64 crc, const void *p, size_t len)
+{
+	const unsigned char *_p = p;
+	size_t i;
+
+	for (i = 0; i < len; i++)
+		crc = (crc >> 8) ^ crc64rocksofttable[(crc & 0xff) ^ *_p++];
+
+	return crc ^ (u64)~0;
+}
+EXPORT_SYMBOL_GPL(crc64_rocksoft);
diff --git a/lib/gen_crc64table.c b/lib/gen_crc64table.c
index 094b43aef8db..55e222acd0b8 100644
--- a/lib/gen_crc64table.c
+++ b/lib/gen_crc64table.c
@@ -17,10 +17,30 @@
 #include <stdio.h>
 
 #define CRC64_ECMA182_POLY 0x42F0E1EBA9EA3693ULL
+#define CRC64_ROCKSOFT_POLY 0x9A6C9329AC4BC9B5ULL
 
 static uint64_t crc64_table[256] = {0};
+static uint64_t crc64_rocksoft_table[256] = {0};
 
-static void generate_crc64_table(void)
+static void generate_reflected_crc64_table(uint64_t table[256], uint64_t poly)
+{
+	uint64_t i, j, c, crc;
+
+	for (i = 0; i < 256; i++) {
+		crc = 0ULL;
+		c = i;
+
+		for (j = 0; j < 8; j++) {
+			if ((crc ^ (c >> j)) & 1)
+				crc = (crc >> 1) ^ poly;
+			else
+				crc >>= 1;
+		}
+		table[i] = crc;
+	}
+}
+
+static void generate_crc64_table(uint64_t table[256], uint64_t poly)
 {
 	uint64_t i, j, c, crc;
 
@@ -30,26 +50,22 @@ static void generate_crc64_table(void)
 
 		for (j = 0; j < 8; j++) {
 			if ((crc ^ c) & 0x8000000000000000ULL)
-				crc = (crc << 1) ^ CRC64_ECMA182_POLY;
+				crc = (crc << 1) ^ poly;
 			else
 				crc <<= 1;
 			c <<= 1;
 		}
 
-		crc64_table[i] = crc;
+		table[i] = crc;
 	}
 }
 
-static void print_crc64_table(void)
+static void output_table(uint64_t table[256])
 {
 	int i;
 
-	printf("/* this file is generated - do not edit */\n\n");
-	printf("#include <linux/types.h>\n");
-	printf("#include <linux/cache.h>\n\n");
-	printf("static const u64 ____cacheline_aligned crc64table[256] = {\n");
 	for (i = 0; i < 256; i++) {
-		printf("\t0x%016" PRIx64 "ULL", crc64_table[i]);
+		printf("\t0x%016" PRIx64 "ULL", table[i]);
 		if (i & 0x1)
 			printf(",\n");
 		else
@@ -58,9 +74,22 @@ static void print_crc64_table(void)
 	printf("};\n");
 }
 
+static void print_crc64_tables(void)
+{
+	printf("/* this file is generated - do not edit */\n\n");
+	printf("#include <linux/types.h>\n");
+	printf("#include <linux/cache.h>\n\n");
+	printf("static const u64 ____cacheline_aligned crc64table[256] = {\n");
+	output_table(crc64_table);
+
+	printf("\nstatic const u64 ____cacheline_aligned crc64rocksofttable[256] = {\n");
+	output_table(crc64_rocksoft_table);
+}
+
 int main(int argc, char *argv[])
 {
-	generate_crc64_table();
-	print_crc64_table();
+	generate_crc64_table(crc64_table, CRC64_ECMA182_POLY);
+	generate_reflected_crc64_table(crc64_rocksoft_table, CRC64_ROCKSOFT_POLY);
+	print_crc64_tables();
 	return 0;
 }
-- 
2.25.4