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lib/crc7: Shift crc7() output left 1 bit
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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 <[email protected]>
Reviewed-by: Pavel Machek <[email protected]>
Acked-by: Ulf Hansson <[email protected]>
Signed-off-by: John W. Linville <[email protected]>
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@linvjw
George Spelvin authored and linvjw committed May 16, 2014
1 parent d91a48c commit 1836eea
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Showing 7 changed files with 53 additions and 49 deletions.
2 changes: 1 addition & 1 deletion drivers/mmc/host/mmc_spi.c
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Expand Up @@ -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
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1 change: 0 additions & 1 deletion drivers/net/wireless/ti/wl1251/acx.c
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Expand Up @@ -2,7 +2,6 @@

#include <linux/module.h>
#include <linux/slab.h>
#include <linux/crc7.h>

#include "wl1251.h"
#include "reg.h"
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1 change: 0 additions & 1 deletion drivers/net/wireless/ti/wl1251/cmd.c
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Expand Up @@ -2,7 +2,6 @@

#include <linux/module.h>
#include <linux/slab.h>
#include <linux/crc7.h>
#include <linux/etherdevice.h>

#include "wl1251.h"
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3 changes: 1 addition & 2 deletions drivers/net/wireless/ti/wl1251/spi.c
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Expand Up @@ -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;
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3 changes: 1 addition & 2 deletions drivers/net/wireless/ti/wlcore/spi.c
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Expand Up @@ -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;
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8 changes: 4 additions & 4 deletions include/linux/crc7.h
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Expand Up @@ -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
84 changes: 46 additions & 38 deletions lib/crc7.c
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Expand Up @@ -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
Expand All @@ -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");

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