/* gprs_rlcmac.cpp
 *
 * Copyright (C) 2012 Ivan Klyuchnikov
 * Copyright (C) 2012 Andreas Eversberg <jolly@eversberg.eu>
 * Copyright (C) 2013 by Holger Hans Peter Freyther
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
 */

#include <gprs_rlcmac.h>
#include <gprs_debug.h>
#include <bts.h>
#include <tbf.h>
#include <tbf_ul.h>
#include <pdch.h>
#include <gprs_ms.h>
#include <pcu_utils.h>

#include <errno.h>
#include <values.h>

extern "C" {
#include "mslot_class.h"
#include <osmocom/core/linuxlist.h>
#include <osmocom/core/logging.h>
#include <osmocom/core/utils.h>
}

/* Consider a PDCH as idle if has at most this number of TBFs assigned to it */
#define PDCH_IDLE_TBF_THRESH	1

#define LOGPSL(tbf, level, fmt, args...) LOGP(DRLCMAC, level, "[%s] " fmt, \
					      (tbf->direction == GPRS_RLCMAC_DL_TBF) ? "DL" : "UL", ## args)

#define LOGPAL(tbf, kind, single, trx_n, level, fmt, args...) LOGPSL(tbf, level, \
								     "algo %s <%s> (suggested TRX: %d): " fmt, \
								     kind, single ? "single" : "multi", trx_n, ## args)

static char *set_flag_chars(char *buf, uint8_t val, char set_char, char unset_char = 0)
{
	int i;

	for (i = 0; i < 8; i += 1, val = val >> 1) {
		if (val & 1)
			buf[i] = set_char;
		else if (unset_char)
			buf[i] = unset_char;
	}

	return buf;
}

static uint8_t find_possible_pdchs(const struct gprs_rlcmac_trx *trx, uint8_t max_slots, uint8_t mask,
				   const char *mask_reason = NULL)
{
	unsigned ts;
	uint8_t valid_ts_set = 0;
	int8_t last_tsc = -1; /* must be signed */

	for (ts = 0; ts < ARRAY_SIZE(trx->pdch); ts++) {
		const struct gprs_rlcmac_pdch *pdch;

		pdch = &trx->pdch[ts];
		if (!pdch->is_enabled()) {
			LOGP(DRLCMAC, LOGL_DEBUG, "- Skipping TS %d, because "
				"not enabled\n", ts);
			continue;
		}

		if (((1 << ts) & mask) == 0) {
			if (mask_reason)
				LOGP(DRLCMAC, LOGL_DEBUG,
					"- Skipping TS %d, because %s\n",
					ts, mask_reason);
			continue;
		}

		if (max_slots > 1) {
			/* check if TSC changes, see TS 45.002, 6.4.2 */
			if (last_tsc < 0)
				last_tsc = pdch->tsc;
			else if (last_tsc != pdch->tsc) {
				LOGP(DRLCMAC, LOGL_ERROR,
					"Skipping TS %d of TRX=%d, because it "
					"has different TSC than lower TS of TRX. "
					"In order to allow multislot, all "
					"slots must be configured with the same "
					"TSC!\n", ts, trx->trx_no);
				continue;
			}
		}

		valid_ts_set |= 1 << ts;
	}

	return valid_ts_set;
}

static int compute_usage_by_num_tbfs(const struct gprs_rlcmac_pdch *pdch, enum gprs_rlcmac_tbf_direction dir)
{
	return pdch->num_tbfs(dir);
}

static int compute_usage_by_reservation(const struct gprs_rlcmac_pdch *pdch, enum gprs_rlcmac_tbf_direction)
{
	return
		pdch->num_reserved(GPRS_RLCMAC_DL_TBF) +
		pdch->num_reserved(GPRS_RLCMAC_UL_TBF);
}

static int compute_usage_for_algo_a(const struct gprs_rlcmac_pdch *pdch, enum gprs_rlcmac_tbf_direction dir)
{
	int usage =
		pdch->num_tbfs(GPRS_RLCMAC_DL_TBF) +
		pdch->num_tbfs(GPRS_RLCMAC_UL_TBF) +
		compute_usage_by_reservation(pdch, dir);

	if (pdch->assigned_tfi(reverse(dir)) == NO_FREE_TFI)
		/* No TFI in the opposite direction, avoid it */
		usage += 32;

	return usage;

}

/*! Return the TS which corresponds to least busy PDCH
 *
 *  \param[in] trx Pointer to TRX object
 *  \param[in] dir TBF direction
 *  \param[in] mask set of available timeslots
 *  \param[in] fn Function pointer to function which computes number of associated TBFs
 *  \param[out] free_tfi Free TFI
 *  \param[out] free_usf Free USF
 *  \returns TS number or -1 if unable to find
 */
static int find_least_busy_pdch(const struct gprs_rlcmac_trx *trx, enum gprs_rlcmac_tbf_direction dir, uint8_t mask,
				int (*fn)(const struct gprs_rlcmac_pdch *, enum gprs_rlcmac_tbf_direction dir),
				int *free_tfi = 0, int *free_usf = 0)
{
	unsigned ts;
	int min_used = INT_MAX;
	int min_ts = -1;
	int min_tfi = -1;
	int min_usf = -1;

	for (ts = 0; ts < ARRAY_SIZE(trx->pdch); ts++) {
		const struct gprs_rlcmac_pdch *pdch = &trx->pdch[ts];
		int num_tbfs;
		int usf = -1; /* must be signed */
		int tfi = -1;

		if (((1 << ts) & mask) == 0)
			continue;

		num_tbfs = fn(pdch, dir);

		if (num_tbfs < min_used) {
			/* We have found a candidate */
			/* Make sure that a TFI is available */
			if (free_tfi) {
				tfi = find_free_tfi(pdch->assigned_tfi(dir));
				if (tfi < 0) {
					LOGP(DRLCMAC, LOGL_DEBUG,
						"- Skipping TS %d, because "
						"no TFI available\n", ts);
					continue;
				}
			}
			/* Make sure that an USF is available */
			if (dir == GPRS_RLCMAC_UL_TBF) {
				usf = find_free_usf(pdch->assigned_usf());
				if (usf < 0) {
					LOGP(DRLCMAC, LOGL_DEBUG,
						"- Skipping TS %d, because "
						"no USF available\n", ts);
					continue;
				}
			}
			if (min_ts >= 0)
				LOGP(DRLCMAC, LOGL_DEBUG,
					"- Skipping TS %d, because "
					"num TBFs %d > %d\n",
					min_ts, min_used, num_tbfs);
			min_used = num_tbfs;
			min_ts = ts;
			min_tfi = tfi;
			min_usf = usf;
		} else {
			LOGP(DRLCMAC, LOGL_DEBUG,
				"- Skipping TS %d, because "
				"num TBFs %d >= %d\n",
				ts, num_tbfs, min_used);
		}
	}

	if (min_ts < 0)
		return -1;

	if (free_tfi)
		*free_tfi = min_tfi;
	if (free_usf)
		*free_usf = min_usf;

	return min_ts;
}

static void attach_tbf_to_pdch(struct gprs_rlcmac_pdch *pdch,
	struct gprs_rlcmac_tbf *tbf)
{
	if (tbf->pdch[pdch->ts_no])
		tbf->pdch[pdch->ts_no]->detach_tbf(tbf);

	tbf->pdch[pdch->ts_no] = pdch;
	pdch->attach_tbf(tbf);
}

static void assign_uplink_tbf_usf(struct gprs_rlcmac_pdch *pdch, struct gprs_rlcmac_ul_tbf *tbf, uint8_t tfi, int8_t usf)
{
	tbf->m_tfi = tfi;
	tbf->m_usf[pdch->ts_no] = usf;
	attach_tbf_to_pdch(pdch, tbf);
}

static void assign_dlink_tbf(struct gprs_rlcmac_pdch *pdch, struct gprs_rlcmac_dl_tbf *tbf, uint8_t tfi)
{
	tbf->m_tfi = tfi;
	attach_tbf_to_pdch(pdch, tbf);
}

static int find_trx(const struct gprs_rlcmac_bts *bts_data, const GprsMs *ms, int8_t use_trx)
{
	unsigned trx_no;
	unsigned ts;

	/* We must use the TRX currently actively used by an MS */
	if (ms && ms_current_trx(ms))
		return ms_current_trx(ms)->trx_no;

	if (use_trx >= 0 && use_trx < 8)
		return use_trx;

	/* Find the first TRX that has a PDCH with a free UL and DL TFI */
	for (trx_no = 0; trx_no < ARRAY_SIZE(bts_data->trx); trx_no += 1) {
		const struct gprs_rlcmac_trx *trx = &bts_data->trx[trx_no];
		for (ts = 0; ts < ARRAY_SIZE(trx->pdch); ts++) {
			const struct gprs_rlcmac_pdch *pdch = &trx->pdch[ts];
			if (!pdch->is_enabled())
				continue;

			if (pdch->assigned_tfi(GPRS_RLCMAC_UL_TBF) == NO_FREE_TFI)
				continue;

			if (pdch->assigned_tfi(GPRS_RLCMAC_DL_TBF) == NO_FREE_TFI)
				continue;

			return trx_no;
		}
	}

	return -EBUSY;
}

static bool idle_pdch_avail(const struct gprs_rlcmac_bts *bts_data)
{
	unsigned trx_no;
	unsigned ts;

	/* Find the first PDCH with an unused DL TS */
	for (trx_no = 0; trx_no < ARRAY_SIZE(bts_data->trx); trx_no += 1) {
		const struct gprs_rlcmac_trx *trx = &bts_data->trx[trx_no];
		for (ts = 0; ts < ARRAY_SIZE(trx->pdch); ts++) {
			const struct gprs_rlcmac_pdch *pdch = &trx->pdch[ts];
			if (!pdch->is_enabled())
				continue;

			if (pdch->num_tbfs(GPRS_RLCMAC_DL_TBF) > PDCH_IDLE_TBF_THRESH)
				continue;

			return true;
		}
	}

	return false;
}

/*! Return free TFI
 *
 *  \param[in] bts Pointer to BTS struct
 *  \param[in] trx Optional pointer to TRX struct
 *  \param[in] ms Pointer to MS object
 *  \param[in] dir DL or UL direction
 *  \param[in] use_trx which TRX to use or -1 if it should be selected based on what MS uses
 *  \param[out] trx_no_ TRX number on which TFI was found
 *  \returns negative error code or 0 on success
 */
static int tfi_find_free(const BTS *bts, const gprs_rlcmac_trx *trx, const GprsMs *ms,
			 enum gprs_rlcmac_tbf_direction dir, int8_t use_trx, uint8_t *trx_no_)
{
	int tfi;
	uint8_t trx_no;

	if (trx) {
		if (use_trx >= 0 && use_trx != trx->trx_no) {
			LOGP(DRLCMAC, LOGL_ERROR, "- Requested incompatible TRX %d (current is %d)\n",
			     use_trx, trx->trx_no);
			return -EINVAL;
		}
		use_trx = trx->trx_no;
	}

	if (use_trx == -1 && ms_current_trx(ms))
		use_trx = ms_current_trx(ms)->trx_no;

	tfi = bts->tfi_find_free(dir, &trx_no, use_trx);
	if (tfi < 0)
		return -EBUSY;

	if (trx_no_)
		*trx_no_ = trx_no;

	return tfi;
}

/*! Slot Allocation: Algorithm A
 *
 * Assign single slot for uplink and downlink
 *
 *  \param[in,out] bts Pointer to BTS struct
 *  \param[in,out] ms_ Pointer to MS object
 *  \param[in,out] tbf_ Pointer to TBF struct
 *  \param[in] single flag indicating if we should force single-slot allocation
 *  \param[in] use_trx which TRX to use or -1 if it should be selected during allocation
 *  \returns negative error code or 0 on success
 */
int alloc_algorithm_a(struct gprs_rlcmac_bts *bts, GprsMs *ms_, struct gprs_rlcmac_tbf *tbf_, bool single,
		      int8_t use_trx)
{
	struct gprs_rlcmac_pdch *pdch;
	int ts = -1;
	uint8_t ul_slots, dl_slots;
	int trx_no;
	int tfi = -1;
	int usf = -1;
	uint8_t mask = 0xff;
	const char *mask_reason = NULL;
	const GprsMs *ms = ms_;
	const gprs_rlcmac_tbf *tbf = tbf_;
	gprs_rlcmac_trx *trx = ms_current_trx(ms);

	LOGPAL(tbf, "A", single, use_trx, LOGL_DEBUG, "Alloc start\n");

	trx_no = find_trx(bts, ms, use_trx);
	if (trx_no < 0) {
		LOGPAL(tbf, "A", single, use_trx, LOGL_NOTICE,
		       "failed to find a usable TRX (TFI exhausted)\n");
		return trx_no;
	}
	if (!trx)
		trx = &bts->trx[trx_no];

	dl_slots = ms_reserved_dl_slots(ms);
	ul_slots = ms_reserved_ul_slots(ms);

	ts = ms_first_common_ts(ms);

	if (ts >= 0) {
		mask_reason = "need to reuse TS";
		mask = 1 << ts;
	} else if (dl_slots || ul_slots) {
		mask_reason = "need to use a reserved common TS";
		mask = dl_slots & ul_slots;
	}

	mask = find_possible_pdchs(trx, 1, mask, mask_reason);
	if (!mask)
		return -EINVAL;

	ts = find_least_busy_pdch(trx, tbf->direction, mask,
		compute_usage_for_algo_a,
		&tfi, &usf);

	if (tbf->direction == GPRS_RLCMAC_UL_TBF && usf < 0) {
		LOGPAL(tbf, "A", single, use_trx, LOGL_NOTICE,
		       "failed to allocate a TS, no USF available\n");
		return -EBUSY;
	}

	if (ts < 0) {
		LOGPAL(tbf, "A", single, use_trx, LOGL_NOTICE,
		       "failed to allocate a TS, no TFI available\n");
		return -EBUSY;
	}

	pdch = &trx->pdch[ts];

	/* The allocation will be successful, so the system state and tbf_/ms_
	 * may be modified from now on. */
	if (tbf->direction == GPRS_RLCMAC_UL_TBF) {
		struct gprs_rlcmac_ul_tbf *ul_tbf = as_ul_tbf(tbf_);
		LOGPSL(tbf, LOGL_DEBUG, "Assign uplink TS=%d TFI=%d USF=%d\n", ts, tfi, usf);
		assign_uplink_tbf_usf(pdch, ul_tbf, tfi, usf);
	} else {
		struct gprs_rlcmac_dl_tbf *dl_tbf = as_dl_tbf(tbf_);
		LOGPSL(tbf, LOGL_DEBUG, "Assign downlink TS=%d TFI=%d\n", ts, tfi);
		assign_dlink_tbf(pdch, dl_tbf, tfi);
	}

	tbf_->trx = trx;
	/* the only one TS is the common TS */
	tbf_->first_ts = tbf_->first_common_ts = ts;
	ms_set_reserved_slots(ms_, trx, 1 << ts, 1 << ts);

	tbf_->upgrade_to_multislot = 0;
	bts->bts->do_rate_ctr_inc(CTR_TBF_ALLOC_ALGO_A);
	return 0;
}

/*! Compute capacity of a given TRX
 *
 *  \param[in] trx Pointer to TRX object
 *  \param[in] rx_window Receive window
 *  \param[in] tx_window Transmit window
 *  \returns non-negative capacity
 */
static inline unsigned compute_capacity(const struct gprs_rlcmac_trx *trx, int rx_window, int tx_window)
{
	const struct gprs_rlcmac_pdch *pdch;
	unsigned ts, capacity = 0;

	for (ts = 0; ts < ARRAY_SIZE(trx->pdch); ts++) {
		pdch = &trx->pdch[ts];
		if (rx_window & (1 << ts))
			capacity += OSMO_MAX(32 - pdch->num_reserved(GPRS_RLCMAC_DL_TBF), 1);

		/* Only consider common slots for UL */
		if (tx_window & rx_window & (1 << ts)) {
			if (find_free_usf(pdch->assigned_usf()) >= 0)
				capacity += OSMO_MAX(32 - pdch->num_reserved(GPRS_RLCMAC_UL_TBF), 1);
		}
	}

	return capacity;
}

/*! Decide if a given slot should be skipped by multislot allocator
 *
 *  \param[in] ms_class Pointer to MS Class object
 *  \param[in] check_tr Flag indicating whether we should check for Tra or Tta parameters for a given MS class
 *  \param[in] rx_window Receive window
 *  \param[in] tx_window Transmit window
 *  \param[in,out] checked_rx array with already checked RX timeslots
 *  \returns true if the slot should be skipped, false otherwise
 */
static bool skip_slot(uint8_t mslot_class, bool check_tr,
		      int16_t rx_window, int16_t tx_window,
		      uint32_t *checked_rx)
{
	uint8_t common_slot_count, req_common_slots,
		rx_slot_count = pcu_bitcount(rx_window),
		tx_slot_count = pcu_bitcount(tx_window);

	/* Check compliance with TS 45.002, table 6.4.2.2.1 */
	/* Whether to skip this round doesn not only depend on the bit
	 * sets but also on check_tr. Therefore this check must be done
	 * before doing the mslot_test_and_set_bit shortcut. */
	if (mslot_class_get_type(mslot_class) == 1) {
		uint16_t slot_sum = rx_slot_count + tx_slot_count;
		/* Assume down + up / dynamic.
		 * TODO: For ext-dynamic, down only, up only add more cases.
		 */
		if (slot_sum <= 6 && tx_slot_count < 3) {
			if (!check_tr)
				return true; /* Skip Tta */
		} else if (slot_sum > 6 && tx_slot_count < 3) {
			if (check_tr)
				return true; /* Skip Tra */
		} else
			return true; /* No supported row in TS 45.002, table 6.4.2.2.1. */
	}

	/* Avoid repeated RX combination check */
	if (mslot_test_and_set_bit(checked_rx, rx_window))
		return true;

	/* Check number of common slots according to TS 45.002, §6.4.2.2 */
	common_slot_count = pcu_bitcount(tx_window & rx_window);
	req_common_slots = OSMO_MIN(tx_slot_count, rx_slot_count);
	if (mslot_class_get_type(mslot_class) == 1)
		req_common_slots = OSMO_MIN(req_common_slots, 2);

	if (req_common_slots != common_slot_count)
		return true;

	return false;
}

/*! Find set of slots available for allocation while taking MS class into account
 *
 *  \param[in] trx Pointer to TRX object
 *  \param[in] mslot_class The multislot class
 *  \param[in,out] ul_slots set of UL timeslots
 *  \param[in,out] dl_slots set of DL timeslots
 *  \returns negative error code or 0 on success
 */
int find_multi_slots(struct gprs_rlcmac_trx *trx, uint8_t mslot_class, uint8_t *ul_slots, uint8_t *dl_slots)
{
	uint8_t Tx = mslot_class_get_tx(mslot_class),   /* Max number of Tx slots */
		Sum = mslot_class_get_sum(mslot_class), /* Max number of Tx + Rx slots */
		max_slots, num_tx, mask_sel, pdch_slots, ul_ts, dl_ts;
	int16_t rx_window, tx_window;
	char slot_info[9] = {0};
	int max_capacity = -1;
	uint8_t max_ul_slots = 0, max_dl_slots = 0;

	if (mslot_class)
		LOGP(DRLCMAC, LOGL_DEBUG, "Slot Allocation (Algorithm B) for class %d\n",
		     mslot_class);

	if (Tx == MS_NA) {
		LOGP(DRLCMAC, LOGL_NOTICE, "Multislot class %d not applicable.\n",
		     mslot_class);
		return -EINVAL;
	}

	max_slots = OSMO_MAX(mslot_class_get_rx(mslot_class), Tx);

	if (*dl_slots == 0)
		*dl_slots = 0xff;

	if (*ul_slots == 0)
		*ul_slots = 0xff;

	pdch_slots = find_possible_pdchs(trx, max_slots, 0xff);

	*dl_slots &= pdch_slots;
	*ul_slots &= pdch_slots;

	LOGP(DRLCMAC, LOGL_DEBUG, "- Possible DL/UL slots: (TS=0)\"%s\"(TS=7)\n",
		set_flag_chars(set_flag_chars(set_flag_chars(slot_info,
				*dl_slots, 'D', '.'),
				*ul_slots, 'U'),
				*ul_slots & *dl_slots, 'C'));

	/* Check for each UL (TX) slot */

	/* Iterate through possible numbers of TX slots */
	for (num_tx = 1; num_tx <= mslot_class_get_tx(mslot_class); num_tx += 1) {
		uint16_t tx_valid_win = (1 << num_tx) - 1;
		uint8_t rx_mask[MASK_TR + 1];

		mslot_fill_rx_mask(mslot_class, num_tx, rx_mask);

		/* Rotate group of TX slots: UUU-----, -UUU----, ..., UU-----U */
		for (ul_ts = 0; ul_ts < 8; ul_ts += 1, tx_valid_win <<= 1) {
			uint16_t rx_valid_win;
			uint32_t checked_rx[256/32] = {0};

			/* Wrap valid window */
			tx_valid_win = mslot_wrap_window(tx_valid_win);

			tx_window = tx_valid_win;

			/* Filter out unavailable slots */
			tx_window &= *ul_slots;

			/* Skip if the the first TS (ul_ts) is not in the set */
			if ((tx_window & (1 << ul_ts)) == 0)
				continue;

			/* Skip if the the last TS (ul_ts+num_tx-1) is not in the set */
			if ((tx_window & (1 << ((ul_ts+num_tx-1) % 8))) == 0)
				continue;

			rx_valid_win = (1 << OSMO_MIN(mslot_class_get_rx(mslot_class), Sum - num_tx)) - 1;

			/* Rotate group of RX slots: DDD-----, -DDD----, ..., DD-----D */
			for (dl_ts = 0; dl_ts < 8; dl_ts += 1, rx_valid_win <<= 1) {
				/* Wrap valid window */
				rx_valid_win = (rx_valid_win | rx_valid_win >> 8) & 0xff;

				/* Validate with both Tta/Ttb/Trb and Ttb/Tra/Trb */
				for (mask_sel = MASK_TT; mask_sel <= MASK_TR; mask_sel += 1) {
					int capacity;

					rx_window = mslot_filter_bad(rx_mask[mask_sel], ul_ts, *dl_slots, rx_valid_win);
					if (rx_window < 0)
						continue;

					if (skip_slot(mslot_class, mask_sel != MASK_TT, rx_window, tx_window, checked_rx))
						continue;

					/* Compute capacity */
					capacity = compute_capacity(trx, rx_window, tx_window);

#ifdef ENABLE_TS_ALLOC_DEBUG
					LOGP(DRLCMAC, LOGL_DEBUG,
						"- Considering DL/UL slots: (TS=0)\"%s\"(TS=7), "
						"capacity = %d\n",
						set_flag_chars(set_flag_chars(set_flag_chars(set_flag_chars(
								slot_info,
								rx_bad, 'x', '.'),
								rx_window, 'D'),
								tx_window, 'U'),
								rx_window & tx_window, 'C'),
						capacity);
#endif

					if (capacity <= max_capacity)
						continue;

					max_capacity = capacity;
					max_ul_slots = tx_window;
					max_dl_slots = rx_window;
				}
			}
		}
	}

	if (!max_ul_slots || !max_dl_slots) {
		LOGP(DRLCMAC, LOGL_NOTICE,
			"No valid UL/DL slot combination found\n");
		return -EINVAL;
	}

	*ul_slots = max_ul_slots;
	*dl_slots = max_dl_slots;

	return 0;
}

/*! Count used bits in slots and reserved_slots bitmasks
 *
 *  \param[in] slots Timeslots in use
 *  \param[in] reserved_slots Reserved timeslots
 *  \param[out] slotcount Number of TS in use
 *  \param[out] avail_count Number of reserved TS
 */
static void update_slot_counters(uint8_t slots, uint8_t reserved_slots, uint8_t *slotcount, uint8_t *avail_count)
{
	(*slotcount) = pcu_bitcount(slots);
	(*avail_count) = pcu_bitcount(reserved_slots);
}

/*! Return slot mask with single TS from a given UL/DL set according to TBF's direction, ts pointer is set to that TS
 * number or to negative value on error
 *
 *  \param[in] trx Pointer to TRX object
 *  \param[in] tbf Pointer to TBF object
 *  \param[in] dl_slots set of DL timeslots
 *  \param[in] ul_slots set of UL timeslots
 *  \param[in] ts corresponding TS or -1 for autoselection
 *  \returns slot mask with single UL or DL timeslot number if possible
 */
static uint8_t get_single_ts(const gprs_rlcmac_trx *trx, const gprs_rlcmac_tbf *tbf, uint8_t dl_slots, uint8_t ul_slots,
			     int ts)
{
	uint8_t ret = dl_slots & ul_slots; /* Make sure to consider the first common slot only */

	if (ts < 0)
		ts = find_least_busy_pdch(trx, tbf->direction, ret, compute_usage_by_num_tbfs, NULL, NULL);

	if (ts < 0)
		return ffs(ret);

	return ret & (1 << ts);
}

/*! Find set of timeslots available for allocation
 *
 *  \param[in] trx Pointer to TRX object
 *  \param[in] tbf Pointer to TBF object
 *  \param[in] single Flag to force the single TS allocation
 *  \param[in] ul_slots set of UL timeslots
 *  \param[in] dl_slots set of DL timeslots
 *  \param[in] reserved_ul_slots set of reserved UL timeslots
 *  \param[in] reserved_dl_slots set of reserved DL timeslots
 *  \param[in] first_common_ts First TS common for both UL and DL or -1 if unknown
 *  \returns negative error code or selected TS on success
 */
static int tbf_select_slot_set(const gprs_rlcmac_tbf *tbf, const gprs_rlcmac_trx *trx, bool single,
			       uint8_t ul_slots, uint8_t dl_slots,
			       uint8_t reserved_ul_slots, uint8_t reserved_dl_slots,
			       int8_t first_common_ts)
{
	uint8_t sl = tbf->direction != GPRS_RLCMAC_DL_TBF ? ul_slots : dl_slots;
	char slot_info[9] = { 0 };

	if (single)
		sl = get_single_ts(trx, tbf, dl_slots, ul_slots, first_common_ts);

	if (!sl) {
		LOGP(DRLCMAC, LOGL_NOTICE, "No %s slots available\n",
		     tbf->direction != GPRS_RLCMAC_DL_TBF ? "uplink" : "downlink");
		return -EINVAL;
	}

	if (tbf->direction != GPRS_RLCMAC_DL_TBF) {
		snprintf(slot_info, 9, OSMO_BIT_SPEC, OSMO_BIT_PRINT_EX(reserved_ul_slots, 'u'));
		masked_override_with(slot_info, sl, 'U');
		LOGP(DRLCMAC, LOGL_DEBUG, "- Selected UL");
	} else {
		snprintf(slot_info, 9, OSMO_BIT_SPEC, OSMO_BIT_PRINT_EX(reserved_dl_slots, 'd'));
		masked_override_with(slot_info, sl, 'D');
		LOGP(DRLCMAC, LOGL_DEBUG, "- Selected DL");
	}

	LOGPC(DRLCMAC, LOGL_DEBUG, " slots: (TS=0)\"%s\"(TS=7), %s\n", slot_info, single ? "single" : "multi");

	return sl;
}

/*! Allocate USF according to a given UL TS mapping
 *
 * N. B: this is legacy implementation which ignores given selected_ul_slots
 *  \param[in] trx Pointer to TRX object
 *  \param[in] tbf Pointer to TBF object
 *  \param[in] first_common_ts First TS which is common to both UL and DL
 *  \param[in] selected_ul_slots set of UL timeslots selected for allocation
 *  \param[in] dl_slots set of DL timeslots
 *  \param[out] usf array for allocated USF
 *  \returns updated UL TS or negative on error
 */
static int allocate_usf(const gprs_rlcmac_trx *trx, int8_t first_common_ts, uint8_t selected_ul_slots, uint8_t dl_slots,
			int *usf)
{
	int free_usf = -1, ts;
	uint8_t ul_slots = selected_ul_slots;

	if (first_common_ts >= 0)
		ul_slots = 1 << first_common_ts;
	else
		ul_slots = ul_slots & dl_slots;

	ts = find_least_busy_pdch(trx, GPRS_RLCMAC_UL_TBF, ul_slots, compute_usage_by_num_tbfs, NULL, &free_usf);

	if (free_usf < 0 || ts < 0) {
		LOGP(DRLCMAC, LOGL_NOTICE, "No USF available\n");
		return -EBUSY;
	}

	OSMO_ASSERT(ts >= 0 && ts <= 8);

	/* We will stick to that single UL slot, unreserve the others */
	ul_slots = 1 << ts;
	usf[ts] = free_usf;

	return ul_slots;
}

/*! Update MS' reserved timeslots
 *
 *  \param[in,out] trx Pointer to TRX struct
 *  \param[in,out] ms_ Pointer to MS object
 *  \param[in] tbf_ Pointer to TBF struct
 *  \param[in] res_ul_slots Newly reserved UL slots
 *  \param[in] res_dl_slots Newly reserved DL slots
 *  \param[in] ul_slots available UL slots (for logging only)
 *  \param[in] dl_slots available DL slots (for logging only)
 */
static void update_ms_reserved_slots(gprs_rlcmac_trx *trx, GprsMs *ms, uint8_t res_ul_slots, uint8_t res_dl_slots,
				     uint8_t ul_slots, uint8_t dl_slots)
{
	char slot_info[9] = { 0 };

	if (res_ul_slots == ms_reserved_ul_slots(ms) && res_dl_slots == ms_reserved_dl_slots(ms))
		return;

	/* The reserved slots have changed, update the MS */
	ms_set_reserved_slots(ms, trx, res_ul_slots, res_dl_slots);

	ts_format(slot_info, dl_slots, ul_slots);
	LOGP(DRLCMAC, LOGL_DEBUG, "- Reserved DL/UL slots: (TS=0)\"%s\"(TS=7)\n", slot_info);
}

/*! Assign given UL timeslots to UL TBF
 *
 *  \param[in,out] ul_tbf Pointer to UL TBF struct
 *  \param[in,out] trx Pointer to TRX object
 *  \param[in] ul_slots Set of slots to be assigned
 *  \param[in] tfi selected TFI
 *  \param[in] usf selected USF
 */
static void assign_ul_tbf_slots(struct gprs_rlcmac_ul_tbf *ul_tbf, gprs_rlcmac_trx *trx, uint8_t ul_slots, int tfi,
				int *usf)
{
	uint8_t ts;

	for (ts = 0; ts < 8; ts++) {
		if (!(ul_slots & (1 << ts)))
			continue;

		OSMO_ASSERT(usf[ts] >= 0);

		LOGP(DRLCMAC, LOGL_DEBUG, "- Assigning UL TS %u\n", ts);
		assign_uplink_tbf_usf(&trx->pdch[ts], ul_tbf, tfi, usf[ts]);
	}
}

/*! Assign given DL timeslots to DL TBF
 *
 *  \param[in,out] dl_tbf Pointer to DL TBF struct
 *  \param[in,out] trx Pointer to TRX object
 *  \param[in] ul_slots Set of slots to be assigned
 *  \param[in] tfi selected TFI
 */
static void assign_dl_tbf_slots(struct gprs_rlcmac_dl_tbf *dl_tbf, gprs_rlcmac_trx *trx, uint8_t dl_slots, int tfi)
{
	uint8_t ts;

	for (ts = 0; ts < 8; ts++) {
		if (!(dl_slots & (1 << ts)))
			continue;

		LOGP(DRLCMAC, LOGL_DEBUG, "- Assigning DL TS %u\n", ts);
		assign_dlink_tbf(&trx->pdch[ts], dl_tbf, tfi);
	}
}

/*! Slot Allocation: Algorithm B
 *
 * Assign as many downlink slots as possible.
 * Assign one uplink slot. (With free USF)
 *
 *  \param[in,out] bts Pointer to BTS struct
 *  \param[in,out] ms_ Pointer to MS object
 *  \param[in,out] tbf_ Pointer to TBF struct
 *  \param[in] single flag indicating if we should force single-slot allocation
 *  \param[in] use_trx which TRX to use or -1 if it should be selected during allocation
 *  \returns negative error code or 0 on success
 */
int alloc_algorithm_b(struct gprs_rlcmac_bts *bts, GprsMs *ms_, struct gprs_rlcmac_tbf *tbf_, bool single,
		      int8_t use_trx)
{
	uint8_t dl_slots;
	uint8_t ul_slots;
	uint8_t reserved_dl_slots;
	uint8_t reserved_ul_slots;
	int8_t first_common_ts;
	uint8_t slotcount = 0;
	uint8_t avail_count = 0, trx_no;
	int first_ts = -1;
	int usf[8] = {-1, -1, -1, -1, -1, -1, -1, -1};
	int rc;
	int tfi;
	const GprsMs *ms = ms_;
	const gprs_rlcmac_tbf *tbf = tbf_;
	gprs_rlcmac_trx *trx;

	LOGPAL(tbf, "B", single, use_trx, LOGL_DEBUG, "Alloc start\n");

	/* Step 1: Get current state from the MS object */

	if (!ms) {
		LOGP(DRLCMAC, LOGL_ERROR, "MS not set\n");
		return -EINVAL;
	}

	dl_slots = ms_reserved_dl_slots(ms);
	ul_slots = ms_reserved_ul_slots(ms);
	first_common_ts = ms_first_common_ts(ms);
	trx = ms_current_trx(ms);

	/* Step 2a: Find usable TRX and TFI */
	tfi = tfi_find_free(bts->bts, trx, ms, tbf->direction, use_trx, &trx_no);
	if (tfi < 0) {
		LOGPAL(tbf, "B", single, use_trx, LOGL_NOTICE, "failed to allocate a TFI\n");
		return tfi;
	}

	/* Step 2b: Reserve slots on the TRX for the MS */
	if (!trx)
		trx = &bts->trx[trx_no];

	if (!dl_slots || !ul_slots) {
		rc = find_multi_slots(trx, ms_ms_class(ms), &ul_slots, &dl_slots);
		if (rc < 0)
			return rc;
	}

	reserved_dl_slots = dl_slots;
	reserved_ul_slots = ul_slots;

	/* Step 3a: Derive the slot set for the current TBF */
	rc = tbf_select_slot_set(tbf, trx, single, ul_slots, dl_slots, reserved_ul_slots, reserved_dl_slots,
				 first_common_ts);
	if (rc < 0)
		return -EINVAL;

	/* Step 3b: Derive the slot set for a given direction */
	if (tbf->direction == GPRS_RLCMAC_DL_TBF) {
		dl_slots = rc;
		update_slot_counters(dl_slots, reserved_dl_slots, &slotcount, &avail_count);
	} else {
		rc = allocate_usf(trx, first_common_ts, rc, dl_slots, usf);
		if (rc < 0)
			return rc;

		/* We will stick to that single UL slot, unreserve the others */
		ul_slots = rc;
		reserved_ul_slots = ul_slots;

		update_slot_counters(ul_slots, reserved_ul_slots, &slotcount, &avail_count);
	}

	first_ts = ffs(rc) - 1;
	first_common_ts = ffs(dl_slots & ul_slots) - 1;

	if (first_common_ts < 0) {
		LOGPAL(tbf, "B", single, use_trx, LOGL_NOTICE, "first common slot unavailable\n");
		return -EINVAL;
	}

	if (first_ts < 0) {
		LOGPAL(tbf, "B", single, use_trx, LOGL_NOTICE, "first slot unavailable\n");
		return -EINVAL;
	}

	if (single && slotcount) {
		tbf_->upgrade_to_multislot = (avail_count > slotcount);
		LOGPAL(tbf, "B", single, use_trx, LOGL_INFO, "using single slot at TS %d\n", first_ts);
	} else {
		tbf_->upgrade_to_multislot = 0;
		LOGPAL(tbf, "B", single, use_trx, LOGL_INFO, "using %d slots\n", slotcount);
	}

	/* The allocation will be successful, so the system state and tbf_/ms_
	 * may be modified from now on. */

	/* Step 4: Update MS and TBF and really allocate the resources */

	update_ms_reserved_slots(trx, ms_, reserved_ul_slots, reserved_dl_slots, ul_slots, dl_slots);

	tbf_->trx = trx;
	tbf_->first_common_ts = first_common_ts;
	tbf_->first_ts = first_ts;

	if (tbf->direction == GPRS_RLCMAC_DL_TBF)
		assign_dl_tbf_slots(as_dl_tbf(tbf_), trx, dl_slots, tfi);
	else
		assign_ul_tbf_slots(as_ul_tbf(tbf_), trx, ul_slots, tfi, usf);

	bts->bts->do_rate_ctr_inc(CTR_TBF_ALLOC_ALGO_B);

	return 0;
}

/*! Slot Allocation: Algorithm dynamic
 *
 * This meta algorithm automatically selects on of the other algorithms based
 * on the current system state.
 *
 * The goal is to support as many MS and TBF as possible. On low usage, the
 * goal is to provide the highest possible bandwidth per MS.
 *
 *  \param[in,out] bts Pointer to BTS struct
 *  \param[in,out] ms_ Pointer to MS object
 *  \param[in,out] tbf_ Pointer to TBF struct
 *  \param[in] single flag indicating if we should force single-slot allocation
 *  \param[in] use_trx which TRX to use or -1 if it should be selected during allocation
 *  \returns negative error code or 0 on success
 */
int alloc_algorithm_dynamic(struct gprs_rlcmac_bts *bts, GprsMs *ms_, struct gprs_rlcmac_tbf *tbf_, bool single,
			    int8_t use_trx)
{
	int rc;

	/* Reset load_is_high if there is at least one idle PDCH */
	if (bts->multislot_disabled) {
		bts->multislot_disabled = !idle_pdch_avail(bts);
		if (!bts->multislot_disabled)
			LOGP(DRLCMAC, LOGL_DEBUG, "Enabling algorithm B\n");
	}

	if (!bts->multislot_disabled) {
		rc = alloc_algorithm_b(bts, ms_, tbf_, single, use_trx);
		if (rc >= 0)
			return rc;

		if (!bts->multislot_disabled)
			LOGP(DRLCMAC, LOGL_DEBUG, "Disabling algorithm B\n");
		bts->multislot_disabled = 1;
	}

	return alloc_algorithm_a(bts, ms_, tbf_, single, use_trx);
}

int gprs_alloc_max_dl_slots_per_ms(const struct gprs_rlcmac_bts *bts, uint8_t ms_class)
{
	int rx = mslot_class_get_rx(ms_class);

	if (rx == MS_NA)
		rx = 4;

	if (bts->alloc_algorithm == alloc_algorithm_a)
		return 1;

	if (bts->multislot_disabled)
		return 1;

	return rx;
}