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