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

From: Pavel Machek
Date: Sun May 11 2014 - 04:28:41 EST

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In reply to: George Spelvin: "[PATCH] lib/crc7: Shift crc7() output left 1 bit"
Next in thread: George Spelvin: "Re: [PATCH] lib/crc7: Shift crc7() output left 1 bit"
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On Sun 2014-05-11 00:35:26, George Spelvin wrote:
> This eliminates a 1-bit left shift in every single caller,
> and also makes the inner loop of the CRC computation more efficient.
>
> And purged #include <linux/crc7.h> from files that don't use it at all.

Looks good, but should not function name change when functionality got
completely different?

Pavel

>
> Signed-off-by: George Spelvin <linux@xxxxxxxxxxx>
> ---
> 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 | 2 +-
> lib/crc7.c | 74 ++++++++++++++++++++----------------
> 7 files changed, 45 insertions(+), 41 deletions(-)
>
> diff --git a/drivers/mmc/host/mmc_spi.c b/drivers/mmc/host/mmc_spi.c
> index 0a87e56913..2c9e879c09 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(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..47875fc6be 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(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..8b3e38e453 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(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..d2155dc953 100644
> --- a/include/linux/crc7.h
> +++ b/include/linux/crc7.h
> @@ -6,7 +6,7 @@ extern const u8 crc7_syndrome_table[256];
>
> static inline u8 crc7_byte(u8 crc, u8 data)
> {
> - return crc7_syndrome_table[(crc << 1) ^ data];
> + return crc7_syndrome_table[crc ^ data];
> }
>
> extern u8 crc7(u8 crc, const u8 *buffer, size_t len);
> diff --git a/lib/crc7.c b/lib/crc7.c
> index f1c3a144ce..4a73b26e7a 100644
> --- a/lib/crc7.c
> +++ b/lib/crc7.c
> @@ -10,40 +10,45 @@
> #include <linux/crc7.h>
>
>
> -/* Table for CRC-7 (polynomial x^7 + x^3 + 1) */
> +/*
> + * 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_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
> + 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);
>
> @@ -55,6 +60,9 @@ 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)
> {
> --
> 1.9.2

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In reply to: George Spelvin: "[PATCH] lib/crc7: Shift crc7() output left 1 bit"
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