lib/crc7: Shift crc7() output left 1 bit
This eliminates a 1-bit left shift in every single caller,
and makes the inner loop of the CRC computation more efficient.
Renamed crc7 to crc7_be (big-endian) since the interface changed.
Also purged #include <linux/crc7.h> from files that don't use it at all.
Signed-off-by: George Spelvin <linux@horizon.com>
Reviewed-by: Pavel Machek <pavel@ucw.cz>
Acked-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/lib/crc7.c b/lib/crc7.c
index f1c3a14..bf6255e 100644
--- a/lib/crc7.c
+++ b/lib/crc7.c
@@ -10,42 +10,47 @@
#include <linux/crc7.h>
-/* Table for CRC-7 (polynomial x^7 + x^3 + 1) */
-const u8 crc7_syndrome_table[256] = {
- 0x00, 0x09, 0x12, 0x1b, 0x24, 0x2d, 0x36, 0x3f,
- 0x48, 0x41, 0x5a, 0x53, 0x6c, 0x65, 0x7e, 0x77,
- 0x19, 0x10, 0x0b, 0x02, 0x3d, 0x34, 0x2f, 0x26,
- 0x51, 0x58, 0x43, 0x4a, 0x75, 0x7c, 0x67, 0x6e,
- 0x32, 0x3b, 0x20, 0x29, 0x16, 0x1f, 0x04, 0x0d,
- 0x7a, 0x73, 0x68, 0x61, 0x5e, 0x57, 0x4c, 0x45,
- 0x2b, 0x22, 0x39, 0x30, 0x0f, 0x06, 0x1d, 0x14,
- 0x63, 0x6a, 0x71, 0x78, 0x47, 0x4e, 0x55, 0x5c,
- 0x64, 0x6d, 0x76, 0x7f, 0x40, 0x49, 0x52, 0x5b,
- 0x2c, 0x25, 0x3e, 0x37, 0x08, 0x01, 0x1a, 0x13,
- 0x7d, 0x74, 0x6f, 0x66, 0x59, 0x50, 0x4b, 0x42,
- 0x35, 0x3c, 0x27, 0x2e, 0x11, 0x18, 0x03, 0x0a,
- 0x56, 0x5f, 0x44, 0x4d, 0x72, 0x7b, 0x60, 0x69,
- 0x1e, 0x17, 0x0c, 0x05, 0x3a, 0x33, 0x28, 0x21,
- 0x4f, 0x46, 0x5d, 0x54, 0x6b, 0x62, 0x79, 0x70,
- 0x07, 0x0e, 0x15, 0x1c, 0x23, 0x2a, 0x31, 0x38,
- 0x41, 0x48, 0x53, 0x5a, 0x65, 0x6c, 0x77, 0x7e,
- 0x09, 0x00, 0x1b, 0x12, 0x2d, 0x24, 0x3f, 0x36,
- 0x58, 0x51, 0x4a, 0x43, 0x7c, 0x75, 0x6e, 0x67,
- 0x10, 0x19, 0x02, 0x0b, 0x34, 0x3d, 0x26, 0x2f,
- 0x73, 0x7a, 0x61, 0x68, 0x57, 0x5e, 0x45, 0x4c,
- 0x3b, 0x32, 0x29, 0x20, 0x1f, 0x16, 0x0d, 0x04,
- 0x6a, 0x63, 0x78, 0x71, 0x4e, 0x47, 0x5c, 0x55,
- 0x22, 0x2b, 0x30, 0x39, 0x06, 0x0f, 0x14, 0x1d,
- 0x25, 0x2c, 0x37, 0x3e, 0x01, 0x08, 0x13, 0x1a,
- 0x6d, 0x64, 0x7f, 0x76, 0x49, 0x40, 0x5b, 0x52,
- 0x3c, 0x35, 0x2e, 0x27, 0x18, 0x11, 0x0a, 0x03,
- 0x74, 0x7d, 0x66, 0x6f, 0x50, 0x59, 0x42, 0x4b,
- 0x17, 0x1e, 0x05, 0x0c, 0x33, 0x3a, 0x21, 0x28,
- 0x5f, 0x56, 0x4d, 0x44, 0x7b, 0x72, 0x69, 0x60,
- 0x0e, 0x07, 0x1c, 0x15, 0x2a, 0x23, 0x38, 0x31,
- 0x46, 0x4f, 0x54, 0x5d, 0x62, 0x6b, 0x70, 0x79
+/*
+ * Table for CRC-7 (polynomial x^7 + x^3 + 1).
+ * This is a big-endian CRC (msbit is highest power of x),
+ * aligned so the msbit of the byte is the x^6 coefficient
+ * and the lsbit is not used.
+ */
+const u8 crc7_be_syndrome_table[256] = {
+ 0x00, 0x12, 0x24, 0x36, 0x48, 0x5a, 0x6c, 0x7e,
+ 0x90, 0x82, 0xb4, 0xa6, 0xd8, 0xca, 0xfc, 0xee,
+ 0x32, 0x20, 0x16, 0x04, 0x7a, 0x68, 0x5e, 0x4c,
+ 0xa2, 0xb0, 0x86, 0x94, 0xea, 0xf8, 0xce, 0xdc,
+ 0x64, 0x76, 0x40, 0x52, 0x2c, 0x3e, 0x08, 0x1a,
+ 0xf4, 0xe6, 0xd0, 0xc2, 0xbc, 0xae, 0x98, 0x8a,
+ 0x56, 0x44, 0x72, 0x60, 0x1e, 0x0c, 0x3a, 0x28,
+ 0xc6, 0xd4, 0xe2, 0xf0, 0x8e, 0x9c, 0xaa, 0xb8,
+ 0xc8, 0xda, 0xec, 0xfe, 0x80, 0x92, 0xa4, 0xb6,
+ 0x58, 0x4a, 0x7c, 0x6e, 0x10, 0x02, 0x34, 0x26,
+ 0xfa, 0xe8, 0xde, 0xcc, 0xb2, 0xa0, 0x96, 0x84,
+ 0x6a, 0x78, 0x4e, 0x5c, 0x22, 0x30, 0x06, 0x14,
+ 0xac, 0xbe, 0x88, 0x9a, 0xe4, 0xf6, 0xc0, 0xd2,
+ 0x3c, 0x2e, 0x18, 0x0a, 0x74, 0x66, 0x50, 0x42,
+ 0x9e, 0x8c, 0xba, 0xa8, 0xd6, 0xc4, 0xf2, 0xe0,
+ 0x0e, 0x1c, 0x2a, 0x38, 0x46, 0x54, 0x62, 0x70,
+ 0x82, 0x90, 0xa6, 0xb4, 0xca, 0xd8, 0xee, 0xfc,
+ 0x12, 0x00, 0x36, 0x24, 0x5a, 0x48, 0x7e, 0x6c,
+ 0xb0, 0xa2, 0x94, 0x86, 0xf8, 0xea, 0xdc, 0xce,
+ 0x20, 0x32, 0x04, 0x16, 0x68, 0x7a, 0x4c, 0x5e,
+ 0xe6, 0xf4, 0xc2, 0xd0, 0xae, 0xbc, 0x8a, 0x98,
+ 0x76, 0x64, 0x52, 0x40, 0x3e, 0x2c, 0x1a, 0x08,
+ 0xd4, 0xc6, 0xf0, 0xe2, 0x9c, 0x8e, 0xb8, 0xaa,
+ 0x44, 0x56, 0x60, 0x72, 0x0c, 0x1e, 0x28, 0x3a,
+ 0x4a, 0x58, 0x6e, 0x7c, 0x02, 0x10, 0x26, 0x34,
+ 0xda, 0xc8, 0xfe, 0xec, 0x92, 0x80, 0xb6, 0xa4,
+ 0x78, 0x6a, 0x5c, 0x4e, 0x30, 0x22, 0x14, 0x06,
+ 0xe8, 0xfa, 0xcc, 0xde, 0xa0, 0xb2, 0x84, 0x96,
+ 0x2e, 0x3c, 0x0a, 0x18, 0x66, 0x74, 0x42, 0x50,
+ 0xbe, 0xac, 0x9a, 0x88, 0xf6, 0xe4, 0xd2, 0xc0,
+ 0x1c, 0x0e, 0x38, 0x2a, 0x54, 0x46, 0x70, 0x62,
+ 0x8c, 0x9e, 0xa8, 0xba, 0xc4, 0xd6, 0xe0, 0xf2
};
-EXPORT_SYMBOL(crc7_syndrome_table);
+EXPORT_SYMBOL(crc7_be_syndrome_table);
/**
* crc7 - update the CRC7 for the data buffer
@@ -55,14 +60,17 @@
* Context: any
*
* Returns the updated CRC7 value.
+ * The CRC7 is left-aligned in the byte (the lsbit is always 0), as that
+ * makes the computation easier, and all callers want it in that form.
+ *
*/
-u8 crc7(u8 crc, const u8 *buffer, size_t len)
+u8 crc7_be(u8 crc, const u8 *buffer, size_t len)
{
while (len--)
- crc = crc7_byte(crc, *buffer++);
+ crc = crc7_be_byte(crc, *buffer++);
return crc;
}
-EXPORT_SYMBOL(crc7);
+EXPORT_SYMBOL(crc7_be);
MODULE_DESCRIPTION("CRC7 calculations");
MODULE_LICENSE("GPL");