26 lines
494 B
C
26 lines
494 B
C
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#include <stdio.h>
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#include "whitening.h"
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void whitening_apply_in_place(uint8_t *data, size_t length)
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{
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/* 9-bit LFSR according to CCITT data whitening procedure. */
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uint16_t lfsr = 0x1FF;
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for(size_t i = 0; i < length; i++) {
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uint8_t byte = 0;
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// advance the LFSR and collect the output in a byte.
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for(int k = 0; k < 8; k++) {
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byte <<= 1;
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byte |= lfsr & 0x001;
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uint16_t tmp = lfsr ^ (lfsr >> 5);
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lfsr >>= 1;
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lfsr |= (tmp & 0x001) << 8;
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}
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data[i] ^= byte;
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}
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}
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