[PATCH v2 1/3] lib/crc7: Shift crc7() output left 1 bit

["George Spelvin" <linux@horizon.com>]

>From 770aa22e6c9c92027e3e21797192ccabb3e7c70e Mon Sep 17 00:00:00 2001
From: George Spelvin <linux@horizon.com>
Date: Sat, 10 May 2014 10:32:57 -0400
Subject: [PATCH v2 1/3] 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>
---
v2: Functions renamed to reflect different results; Pavel Machek
prompted me to think of something not too ugly.

Since all of the affected drivers are officially orphaned, this is
being sent to a hodge-podge of people who touched the files recently.
Assuming the MMC people don't complain, is it okay to send this through
the wireless tree?

 drivers/mmc/host/mmc_spi.c           |  2 +-
 drivers/net/wireless/ti/wl1251/acx.c |  1 -
 drivers/net/wireless/ti/wl1251/cmd.c |  1 -
 drivers/net/wireless/ti/wl1251/spi.c |  3 +-
 drivers/net/wireless/ti/wlcore/spi.c |  3 +-
 include/linux/crc7.h                 |  8 ++--
 lib/crc7.c                           | 84 ++++++++++++++++++++----------------
 7 files changed, 53 insertions(+), 49 deletions(-)

diff --git a/drivers/mmc/host/mmc_spi.c b/drivers/mmc/host/mmc_spi.c
index 0a87e56913..338e2202ea 100644
--- a/drivers/mmc/host/mmc_spi.c
+++ b/drivers/mmc/host/mmc_spi.c
@@ -472,7 +472,7 @@ mmc_spi_command_send(struct mmc_spi_host *host,
 	*cp++ = (u8)(arg >> 16);
 	*cp++ = (u8)(arg >> 8);
 	*cp++ = (u8)arg;
-	*cp++ = (crc7(0, &data->status[1], 5) << 1) | 0x01;
+	*cp++ = crc7_be(0, &data->status[1], 5) | 0x01;
 
 	/* Then, read up to 13 bytes (while writing all-ones):
 	 *  - N(CR) (== 1..8) bytes of all-ones
diff --git a/drivers/net/wireless/ti/wl1251/acx.c b/drivers/net/wireless/ti/wl1251/acx.c
index 5a4ec56c83..5695628757 100644
--- a/drivers/net/wireless/ti/wl1251/acx.c
+++ b/drivers/net/wireless/ti/wl1251/acx.c
@@ -2,7 +2,6 @@
 
 #include <linux/module.h>
 #include <linux/slab.h>
-#include <linux/crc7.h>
 
 #include "wl1251.h"
 #include "reg.h"
diff --git a/drivers/net/wireless/ti/wl1251/cmd.c b/drivers/net/wireless/ti/wl1251/cmd.c
index bf1fa18b97..ede31f048e 100644
--- a/drivers/net/wireless/ti/wl1251/cmd.c
+++ b/drivers/net/wireless/ti/wl1251/cmd.c
@@ -2,7 +2,6 @@
 
 #include <linux/module.h>
 #include <linux/slab.h>
-#include <linux/crc7.h>
 #include <linux/etherdevice.h>
 
 #include "wl1251.h"
diff --git a/drivers/net/wireless/ti/wl1251/spi.c b/drivers/net/wireless/ti/wl1251/spi.c
index b06d36d993..e94b57cd5a 100644
--- a/drivers/net/wireless/ti/wl1251/spi.c
+++ b/drivers/net/wireless/ti/wl1251/spi.c
@@ -122,8 +122,7 @@ static void wl1251_spi_wake(struct wl1251 *wl)
 	crc[3] = cmd[6];
 	crc[4] = cmd[5];
 
-	cmd[4] |= crc7(0, crc, WSPI_INIT_CMD_CRC_LEN) << 1;
-	cmd[4] |= WSPI_INIT_CMD_END;
+	cmd[4] = crc7_be(0, crc, WSPI_INIT_CMD_CRC_LEN) | WSPI_INIT_CMD_END;
 
 	t.tx_buf = cmd;
 	t.len = WSPI_INIT_CMD_LEN;
diff --git a/drivers/net/wireless/ti/wlcore/spi.c b/drivers/net/wireless/ti/wlcore/spi.c
index dbe826dd7c..0497353c4a 100644
--- a/drivers/net/wireless/ti/wlcore/spi.c
+++ b/drivers/net/wireless/ti/wlcore/spi.c
@@ -151,8 +151,7 @@ static void wl12xx_spi_init(struct device *child)
 	crc[3] = cmd[6];
 	crc[4] = cmd[5];
 
-	cmd[4] |= crc7(0, crc, WSPI_INIT_CMD_CRC_LEN) << 1;
-	cmd[4] |= WSPI_INIT_CMD_END;
+	cmd[4] = crc7_be(0, crc, WSPI_INIT_CMD_CRC_LEN) | WSPI_INIT_CMD_END;
 
 	t.tx_buf = cmd;
 	t.len = WSPI_INIT_CMD_LEN;
diff --git a/include/linux/crc7.h b/include/linux/crc7.h
index 1786e772d5..d590765106 100644
--- a/include/linux/crc7.h
+++ b/include/linux/crc7.h
@@ -2,13 +2,13 @@
 #define _LINUX_CRC7_H
 #include <linux/types.h>
 
-extern const u8 crc7_syndrome_table[256];
+extern const u8 crc7_be_syndrome_table[256];
 
-static inline u8 crc7_byte(u8 crc, u8 data)
+static inline u8 crc7_be_byte(u8 crc, u8 data)
 {
-	return crc7_syndrome_table[(crc << 1) ^ data];
+	return crc7_be_syndrome_table[crc ^ data];
 }
 
-extern u8 crc7(u8 crc, const u8 *buffer, size_t len);
+extern u8 crc7_be(u8 crc, const u8 *buffer, size_t len);
 
 #endif
diff --git a/lib/crc7.c b/lib/crc7.c
index f1c3a144ce..bf6255e239 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 @@ EXPORT_SYMBOL(crc7_syndrome_table);
  * 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");
-- 
1.9.2