#include <stdio.h>

#include "whitening.h"

void whitening_apply_in_place(uint8_t *data, size_t length)
{
	/* 9-bit LFSR according to CCITT data whitening procedure. */
	uint16_t lfsr = 0x1FF;

	for(size_t i = 0; i < length; i++) {
		uint8_t byte = 0;

		// advance the LFSR and collect the output in a byte.
		for(int k = 0; k < 8; k++) {
			byte <<= 1;
			byte |= lfsr & 0x001;

			uint16_t tmp = lfsr ^ (lfsr >> 5);
			lfsr >>= 1;
			lfsr |= (tmp & 0x001) << 8;
		}

		data[i] ^= byte;
	}
}