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Date: Wed, 18 Aug 2010 18:10:11 +0200
From: Matthieu CASTET <matthieu.castet@parrot.com>
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To: Joakim Tjernlund <joakim.tjernlund@transmode.se>
Subject: Re: [PATCH 3/4 v2] lib: add crc16_le helper
References: <201008181401.15328.florian@openwrt.org>
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Cc: Artem Bityutskiy <dedekind1@gmail.com>,
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	Maxime Bizon <mbizon@freebox.fr>, David Woodhouse <dwmw2@infradead.org>,
	Florian Fainelli <florian@openwrt.org>, Brian Norris <norris@broadcom.com>
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Hi,

thanks for the review.

Joakim Tjernlund a écrit :
>> This patch adds a crc16_le helper function to lib/crc16.c
>>
>> Signed-off-by: Matthieu CASTET <matthieu.castet@parrot.com>
>> Signed-off-by: Florian Fainelli <ffainelli@freebox.fr>
>> --
>> diff --git a/include/linux/crc16.h b/include/linux/crc16.h
>> index 9443c08..6c1c61f 100644
>> --- a/include/linux/crc16.h
>> +++ b/include/linux/crc16.h
>> @@ -26,5 +26,7 @@ static inline u16 crc16_byte(u16 crc, const u8 data)
>>     return (crc >> 8) ^ crc16_table[(crc ^ data) & 0xff];
>>  }
>>
>> +extern u16 crc16_le(u16 crc, const u8 *buffer, size_t len);
>> +
>>  #endif /* __CRC16_H */
>>
>> diff --git a/lib/crc16.c b/lib/crc16.c
>> index 8737b08..ec4a95c 100644
>> --- a/lib/crc16.c
>> +++ b/lib/crc16.c
>> @@ -62,6 +62,18 @@ u16 crc16(u16 crc, u8 const *buffer, size_t len)
>>  }
>>  EXPORT_SYMBOL(crc16);
>>
>> +u16 crc16_le(u16 crc, u8 const *p, size_t len)
>> +{
>> +   int i;
>> +   while (len--) {
>> +      crc ^= *p++ << 8;
>> +      for (i = 0; i < 8; i++)
>> +         crc = (crc << 1) ^ ((crc & 0x8000) ? 0x8005 : 0);
>> +   }
>> +   return crc;
>> +}
>> +EXPORT_SYMBOL(crc16_le);
>> +
>>  MODULE_DESCRIPTION("CRC16 calculations");
>>  MODULE_LICENSE("GPL");
> 
> Don't recall much of my earlier crc32 work but the above looks wrong.
> crc & 0x8000 suggests this is a big endian crc. 
yes it is a be crc while crc16 is a le one. So we should rename it to 
crc16_be.


>if so, 0x8005 looks
> wrong too. see CRCPOLY_LE resp. CRCPOLY_BE for an idea.
Why ?

> What is this crc sum used for?
Onfi flash parsing in mtd.


Matthieu