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/* Osmocom implementation of pseudo-random bit sequence generation */
/* (C) 2017 by Harald Welte <laforge@gnumonks.org>
* All Rights Reserved
*
* SPDX-License-Identifier: GPL-2.0+
* */
#include <stdint.h>
#include <string.h>
#include <osmocom/core/bits.h>
#include <osmocom/core/prbs.h>
/*! \brief PRBS-7 according ITU-T O.150 */
const struct osmo_prbs osmo_prbs7 = {
/* x^7 + x^6 + 1 */
.name = "PRBS-7",
.len = 7,
.coeff = (1<<6) | (1<<5),
};
/*! \brief PRBS-9 according ITU-T O.150 */
const struct osmo_prbs osmo_prbs9 = {
/* x^9 + x^5 + 1 */
.name = "PRBS-9",
.len = 9,
.coeff = (1<<8) | (1<<4),
};
/*! \brief PRBS-11 according ITU-T O.150 */
const struct osmo_prbs osmo_prbs11 = {
/* x^11 + x^9 + 1 */
.name = "PRBS-11",
.len = 11,
.coeff = (1<<10) | (1<<8),
};
/*! \brief PRBS-15 according ITU-T O.150 */
const struct osmo_prbs osmo_prbs15 = {
/* x^15 + x^14+ 1 */
.name = "PRBS-15",
.len = 15,
.coeff = (1<<14) | (1<<13),
};
/*! \brief Initialize the given caller-allocated PRBS state */
void osmo_prbs_state_init(struct osmo_prbs_state *st, const struct osmo_prbs *prbs)
{
memset(st, 0, sizeof(*st));
st->prbs = prbs;
st->state = 1;
}
static void osmo_prbs_process_bit(struct osmo_prbs_state *state, ubit_t bit)
{
state->state >>= 1;
if (bit)
state->state ^= state->prbs->coeff;
}
/*! \brief Get the next bit out of given PRBS instance */
ubit_t osmo_prbs_get_ubit(struct osmo_prbs_state *state)
{
ubit_t result = state->state & 0x1;
osmo_prbs_process_bit(state, result);
return result;
}
/*! \brief Fill buffer of unpacked bits with next bits out of given PRBS instance */
int osmo_prbs_get_ubits(ubit_t *out, unsigned int out_len, struct osmo_prbs_state *state)
{
unsigned int i;
for (i = 0; i < out_len; i++)
out[i] = osmo_prbs_get_ubit(state);
return i;
}
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