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7799164595
The code comment says that the polynomial is x^16 + x^12 + x^15 + 1, but the correct polynomial is x^16 + x^12 + x^5 + 1. Quoting from page 2 in the ITU-T V.41 specification [1]: 2 Encoding and checking process The service bits and information bits, taken in conjunction, correspond to the coefficients of a message polynomial having terms from x^(n-1) (n = total number of bits in a block or sequence) down to x^16. This polynomial is divided, modulo 2, by the generating polynomial x^16 + x^12 + x^5 + 1. The hex (truncated) polynomial 0x1021 and CRC code implementation are correct, however. [1] https://www.itu.int/rec/T-REC-V.41-198811-I/en Signed-off-by: Roger Knecht <roger@norberthealth.com> Acked-by: Randy Dunlap <rdunlap@infradead.org> Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
26 lines
530 B
C
26 lines
530 B
C
/* SPDX-License-Identifier: GPL-2.0-only */
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/*
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* crc-itu-t.h - CRC ITU-T V.41 routine
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*
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* Implements the standard CRC ITU-T V.41:
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* Width 16
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* Poly 0x1021 (x^16 + x^12 + x^5 + 1)
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* Init 0
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*/
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#ifndef CRC_ITU_T_H
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#define CRC_ITU_T_H
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#include <linux/types.h>
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extern u16 const crc_itu_t_table[256];
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extern u16 crc_itu_t(u16 crc, const u8 *buffer, size_t len);
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static inline u16 crc_itu_t_byte(u16 crc, const u8 data)
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{
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return (crc << 8) ^ crc_itu_t_table[((crc >> 8) ^ data) & 0xff];
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}
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#endif /* CRC_ITU_T_H */
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