/*      $OpenBSD: ieee80211_ra.c,v 1.5 2022/03/19 10:28:44 stsp Exp $   */

/*
 * Copyright (c) 2021 Christian Ehrhardt <ehrhardt@genua.de>
 * Copyright (c) 2016, 2021 Stefan Sperling <stsp@openbsd.org>
 * Copyright (c) 2016 Theo Buehler <tb@openbsd.org>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/socket.h>

#include <net/if.h>
#include <net/if_media.h>

#include <netinet/in.h>
#include <netinet/if_ether.h>

#include <net80211/ieee80211_var.h>
#include <net80211/ieee80211_ra.h>

int     ieee80211_ra_next_intra_rate(struct ieee80211_ra_node *,
            struct ieee80211_node *);
const struct ieee80211_ht_rateset * ieee80211_ra_next_rateset(
                    struct ieee80211_ra_node *, struct ieee80211_node *);
int     ieee80211_ra_best_mcs_in_rateset(struct ieee80211_ra_node *,
            const struct ieee80211_ht_rateset *);
void    ieee80211_ra_probe_next_rateset(struct ieee80211_ra_node *,
            struct ieee80211_node *, const struct ieee80211_ht_rateset *);
int     ieee80211_ra_next_mcs(struct ieee80211_ra_node *,
            struct ieee80211_node *);
void    ieee80211_ra_probe_done(struct ieee80211_ra_node *);
int     ieee80211_ra_intra_mode_ra_finished(
            struct ieee80211_ra_node *, struct ieee80211_node *);
void    ieee80211_ra_trigger_next_rateset(struct ieee80211_ra_node *,
            struct ieee80211_node *);
int     ieee80211_ra_inter_mode_ra_finished(
            struct ieee80211_ra_node *, struct ieee80211_node *);
int     ieee80211_ra_best_rate(struct ieee80211_ra_node *,
            struct ieee80211_node *);
void    ieee80211_ra_probe_next_rate(struct ieee80211_ra_node *,
            struct ieee80211_node *);
int     ieee80211_ra_valid_tx_mcs(struct ieee80211com *, int);
uint32_t ieee80211_ra_valid_rates(struct ieee80211com *,
            struct ieee80211_node *);
int     ieee80211_ra_probe_valid(struct ieee80211_ra_goodput_stats *);

/* We use fixed point arithmetic with 64 bit integers. */
#define RA_FP_SHIFT     21
#define RA_FP_INT(x)    (x ## ULL << RA_FP_SHIFT) /* the integer x */
#define RA_FP_1 RA_FP_INT(1)

/* Multiply two fixed point numbers. */
#define RA_FP_MUL(a, b) \
        (((a) * (b)) >> RA_FP_SHIFT)

/* Divide two fixed point numbers. */
#define RA_FP_DIV(a, b) \
        (b == 0 ? (uint64_t)-1 : (((a) << RA_FP_SHIFT) / (b)))

#ifdef RA_DEBUG
#define DPRINTF(x)      do { if (ra_debug > 0) printf x; } while (0)
#define DPRINTFN(n, x)  do { if (ra_debug >= (n)) printf x; } while (0)
int ra_debug = 0;
#else
#define DPRINTF(x)      do { ; } while (0)
#define DPRINTFN(n, x)  do { ; } while (0)
#endif

#ifdef RA_DEBUG
void
ra_fixedp_split(uint32_t *i, uint32_t *f, uint64_t fp)
{
        uint64_t tmp;

        /* integer part */
        *i = (fp >> RA_FP_SHIFT);

        /* fractional part */
        tmp = (fp & ((uint64_t)-1 >> (64 - RA_FP_SHIFT)));
        tmp *= 100;
        *f = (uint32_t)(tmp >> RA_FP_SHIFT);
}

char *
ra_fp_sprintf(uint64_t fp)
{
        uint32_t i, f;
        static char buf[64];
        int ret;

        ra_fixedp_split(&i, &f, fp);
        ret = snprintf(buf, sizeof(buf), "%u.%02u", i, f);
        if (ret == -1 || ret >= sizeof(buf))
                return "ERR";

        return buf;
}
#endif /* RA_DEBUG */

const struct ieee80211_ht_rateset *
ieee80211_ra_get_ht_rateset(int mcs, int chan40, int sgi)
{
        const struct ieee80211_ht_rateset *rs;
        int i;

        for (i = 0; i < IEEE80211_HT_NUM_RATESETS; i++) {
                rs = &ieee80211_std_ratesets_11n[i];
                if (chan40 == rs->chan40 && sgi == rs->sgi &&
                    mcs >= rs->min_mcs && mcs <= rs->max_mcs)
                        return rs;
        }

        panic("MCS %d is not part of any rateset", mcs);
}

int
ieee80211_ra_use_ht_sgi(struct ieee80211_node *ni)
{
        if ((ni->ni_chan->ic_flags & IEEE80211_CHAN_40MHZ) &&
            ieee80211_node_supports_ht_chan40(ni)) {
                if (ni->ni_flags & IEEE80211_NODE_HT_SGI40)
                        return 1;
        } else if (ni->ni_flags & IEEE80211_NODE_HT_SGI20)
                return 1;
        
        return 0;
}

/*
 * Update goodput statistics.
 */

uint64_t
ieee80211_ra_get_txrate(int mcs, int chan40, int sgi)
{
        const struct ieee80211_ht_rateset *rs;
        uint64_t txrate;

        rs = ieee80211_ra_get_ht_rateset(mcs, chan40, sgi);
        txrate = rs->rates[mcs - rs->min_mcs];
        txrate <<= RA_FP_SHIFT; /* convert to fixed-point */
        txrate *= 500; /* convert to kbit/s */
        txrate /= 1000; /* convert to mbit/s */

        return txrate;
}

/*
 * Rate selection.
 */

/* A rate's goodput has to be at least this much larger to be "better". */
#define IEEE80211_RA_RATE_THRESHOLD     (RA_FP_1 / 64) /* ~ 0.015 */

int
ieee80211_ra_next_lower_intra_rate(struct ieee80211_ra_node *rn,
    struct ieee80211_node *ni)
{
        const struct ieee80211_ht_rateset *rs;
        int i, next;

        rs = ieee80211_ra_get_ht_rateset(ni->ni_txmcs,
            ieee80211_node_supports_ht_chan40(ni), ieee80211_ra_use_ht_sgi(ni));
        if (ni->ni_txmcs == rs->min_mcs)
                return rs->min_mcs;

        next = ni->ni_txmcs;
        for (i = rs->nrates - 1; i >= 0; i--) {
                if ((rn->valid_rates & (1 << (i + rs->min_mcs))) == 0)
                        continue;
                if (i + rs->min_mcs < ni->ni_txmcs) {
                        next = i + rs->min_mcs;
                        break;
                }
        }

        return next;
}

int
ieee80211_ra_next_intra_rate(struct ieee80211_ra_node *rn,
    struct ieee80211_node *ni)
{
        const struct ieee80211_ht_rateset *rs;
        int i, next;

        rs = ieee80211_ra_get_ht_rateset(ni->ni_txmcs,
            ieee80211_node_supports_ht_chan40(ni), ieee80211_ra_use_ht_sgi(ni));
        if (ni->ni_txmcs == rs->max_mcs)
                return rs->max_mcs;

        next = ni->ni_txmcs;
        for (i = 0; i < rs->nrates; i++) {
                if ((rn->valid_rates & (1 << (i + rs->min_mcs))) == 0)
                        continue;
                if (i + rs->min_mcs > ni->ni_txmcs) {
                        next = i + rs->min_mcs;
                        break;
                }
        }

        return next;
}

const struct ieee80211_ht_rateset *
ieee80211_ra_next_rateset(struct ieee80211_ra_node *rn,
    struct ieee80211_node *ni)
{
        const struct ieee80211_ht_rateset *rs, *rsnext;
        int next;
        int chan40 = ieee80211_node_supports_ht_chan40(ni);
        int sgi = ieee80211_ra_use_ht_sgi(ni);
        int mcs = ni->ni_txmcs;

        rs = ieee80211_ra_get_ht_rateset(mcs, chan40, sgi);
        if (rn->probing & IEEE80211_RA_PROBING_UP) {
                if (rs->max_mcs == 7) { /* MCS 0-7 */
                        if (chan40)
                                next = sgi ? IEEE80211_HT_RATESET_MIMO2_SGI40 :
                                    IEEE80211_HT_RATESET_MIMO2_40;
                        else
                                next = sgi ? IEEE80211_HT_RATESET_MIMO2_SGI :
                                    IEEE80211_HT_RATESET_MIMO2;
                } else if (rs->max_mcs == 15) { /* MCS 8-15 */
                        if (chan40)
                                next = sgi ? IEEE80211_HT_RATESET_MIMO3_SGI40 :
                                    IEEE80211_HT_RATESET_MIMO3_40;
                        else
                                next = sgi ? IEEE80211_HT_RATESET_MIMO3_SGI :
                                    IEEE80211_HT_RATESET_MIMO3;
                } else if (rs->max_mcs == 23) { /* MCS 16-23 */
                        if (chan40)
                                next = sgi ? IEEE80211_HT_RATESET_MIMO4_SGI40 :
                                    IEEE80211_HT_RATESET_MIMO4_40;
                        else
                                next = sgi ? IEEE80211_HT_RATESET_MIMO4_SGI :
                                    IEEE80211_HT_RATESET_MIMO4;
                } else                          /* MCS 24-31 */
                        return NULL;
        } else if (rn->probing & IEEE80211_RA_PROBING_DOWN) {
                if (rs->min_mcs == 24) {        /* MCS 24-31 */
                        if (chan40)
                                next = sgi ? IEEE80211_HT_RATESET_MIMO3_SGI40 :
                                    IEEE80211_HT_RATESET_MIMO3_40;
                        else
                                next = sgi ? IEEE80211_HT_RATESET_MIMO3_SGI :
                                    IEEE80211_HT_RATESET_MIMO3;
                } else if (rs->min_mcs == 16) { /* MCS 16-23 */
                        if (chan40)
                                next = sgi ? IEEE80211_HT_RATESET_MIMO2_SGI40 :
                                    IEEE80211_HT_RATESET_MIMO2_40;
                        else
                                next = sgi ? IEEE80211_HT_RATESET_MIMO2_SGI :
                                    IEEE80211_HT_RATESET_MIMO2;
                } else if (rs->min_mcs == 8) {  /* MCS 8-15 */
                        if (chan40)
                                next = sgi ? IEEE80211_HT_RATESET_SISO_SGI40 :
                                    IEEE80211_HT_RATESET_SISO_40;
                        else
                                next = sgi ? IEEE80211_HT_RATESET_SISO_SGI :
                                    IEEE80211_HT_RATESET_SISO;
                } else                          /* MCS 0-7 */
                        return NULL;
        } else
                panic("%s: invalid probing mode %d", __func__, rn->probing);

        rsnext = &ieee80211_std_ratesets_11n[next];
        if ((rsnext->mcs_mask & rn->valid_rates) == 0)
                return NULL;

        return rsnext;
}

int
ieee80211_ra_best_mcs_in_rateset(struct ieee80211_ra_node *rn,
    const struct ieee80211_ht_rateset *rs)
{
        uint64_t gmax = 0;
        int i, best_mcs = rs->min_mcs;

        for (i = 0; i < rs->nrates; i++) {
                int mcs = rs->min_mcs + i;
                struct ieee80211_ra_goodput_stats *g = &rn->g[mcs];
                if (((1 << mcs) & rn->valid_rates) == 0)
                        continue;
                if (g->measured > gmax + IEEE80211_RA_RATE_THRESHOLD) {
                        gmax = g->measured;
                        best_mcs = mcs;
                }
        }

        return best_mcs;
}

void
ieee80211_ra_probe_next_rateset(struct ieee80211_ra_node *rn,
    struct ieee80211_node *ni, const struct ieee80211_ht_rateset *rsnext)
{
        const struct ieee80211_ht_rateset *rs;
        struct ieee80211_ra_goodput_stats *g;
        int best_mcs, i;

        /* Find most recently measured best MCS from the current rateset. */
        rs = ieee80211_ra_get_ht_rateset(ni->ni_txmcs,
            ieee80211_node_supports_ht_chan40(ni), ieee80211_ra_use_ht_sgi(ni));
        best_mcs = ieee80211_ra_best_mcs_in_rateset(rn, rs);

        /* Switch to the next rateset. */
        ni->ni_txmcs = rsnext->min_mcs;
        if ((rn->valid_rates & (1 << rsnext->min_mcs)) == 0)
                ni->ni_txmcs = ieee80211_ra_next_intra_rate(rn, ni);

        /* Select the lowest rate from the next rateset with loss-free
         * goodput close to the current best measurement. */
        g = &rn->g[best_mcs];
        for (i = 0; i < rsnext->nrates; i++) {
                int mcs = rsnext->min_mcs + i;
                uint64_t txrate = rsnext->rates[i];

                if ((rn->valid_rates & (1 << mcs)) == 0)
                        continue;

                txrate = txrate * 500; /* convert to kbit/s */
                txrate <<= RA_FP_SHIFT; /* convert to fixed-point */
                txrate /= 1000; /* convert to mbit/s */

                if (txrate > g->measured + IEEE80211_RA_RATE_THRESHOLD) {
                        ni->ni_txmcs = mcs;
                        break;
                }
        }
        /* If all rates are lower the maximum rate is the closest match. */
        if (i == rsnext->nrates)
                ni->ni_txmcs = rsnext->max_mcs;

        /* Add rates from the next rateset as candidates. */
        rn->candidate_rates |= (1 << ni->ni_txmcs);
        if (rn->probing & IEEE80211_RA_PROBING_UP) {
                rn->candidate_rates |=
                  (1 << ieee80211_ra_next_intra_rate(rn, ni));
        } else if (rn->probing & IEEE80211_RA_PROBING_DOWN) {
                rn->candidate_rates |=
                    (1 << ieee80211_ra_next_lower_intra_rate(rn, ni));
        } else
                panic("%s: invalid probing mode %d", __func__, rn->probing);
}

int
ieee80211_ra_next_mcs(struct ieee80211_ra_node *rn,
    struct ieee80211_node *ni)
{
        int next;

        if (rn->probing & IEEE80211_RA_PROBING_DOWN)
                next = ieee80211_ra_next_lower_intra_rate(rn, ni);
        else if (rn->probing & IEEE80211_RA_PROBING_UP)
                next = ieee80211_ra_next_intra_rate(rn, ni);
        else
                panic("%s: invalid probing mode %d", __func__, rn->probing);

        return next;
}

void
ieee80211_ra_probe_clear(struct ieee80211_ra_node *rn,
    struct ieee80211_node *ni)
{
        struct ieee80211_ra_goodput_stats *g = &rn->g[ni->ni_txmcs];

        g->nprobe_pkts = 0;
        g->nprobe_fail = 0;
}

void
ieee80211_ra_probe_done(struct ieee80211_ra_node *rn)
{
        rn->probing = IEEE80211_RA_NOT_PROBING;
        rn->probed_rates = 0;
        rn->valid_probes = 0;
        rn->candidate_rates = 0;
}

int
ieee80211_ra_intra_mode_ra_finished(struct ieee80211_ra_node *rn,
    struct ieee80211_node *ni)
{
        const struct ieee80211_ht_rateset *rs;
        struct ieee80211_ra_goodput_stats *g = &rn->g[ni->ni_txmcs];
        int next_mcs, best_mcs;
        uint64_t next_rate;
        int chan40 = ieee80211_node_supports_ht_chan40(ni);
        int sgi = ieee80211_ra_use_ht_sgi(ni);

        rn->probed_rates = (rn->probed_rates | (1 << ni->ni_txmcs));

        /* Check if the min/max MCS in this rateset has been probed. */
        rs = ieee80211_ra_get_ht_rateset(ni->ni_txmcs, chan40, sgi);
        if (rn->probing & IEEE80211_RA_PROBING_DOWN) {
                if (ni->ni_txmcs == rs->min_mcs ||
                    rn->probed_rates & (1 << rs->min_mcs)) {
                        ieee80211_ra_trigger_next_rateset(rn, ni);
                        return 1;
                }
        } else if (rn->probing & IEEE80211_RA_PROBING_UP) {
                if (ni->ni_txmcs == rs->max_mcs ||
                    rn->probed_rates & (1 << rs->max_mcs)) {
                        ieee80211_ra_trigger_next_rateset(rn, ni);
                        return 1;
                }
        }

        /*
         * Check if the measured goodput is loss-free and better than the
         * loss-free goodput of the candidate rate.
         */
        next_mcs = ieee80211_ra_next_mcs(rn, ni);
        if (next_mcs == ni->ni_txmcs) {
                ieee80211_ra_trigger_next_rateset(rn, ni);
                return 1;
        }
        next_rate = ieee80211_ra_get_txrate(next_mcs, chan40, sgi);
        if (g->loss == 0 &&
            g->measured >= next_rate + IEEE80211_RA_RATE_THRESHOLD) {
                ieee80211_ra_trigger_next_rateset(rn, ni);
                return 1;
        }

        /* Check if we had a better measurement at a previously probed MCS. */
        best_mcs = ieee80211_ra_best_mcs_in_rateset(rn, rs);
        if (best_mcs != ni->ni_txmcs && (rn->probed_rates & (1 << best_mcs))) {
                if ((rn->probing & IEEE80211_RA_PROBING_UP) &&
                    best_mcs < ni->ni_txmcs) {
                        ieee80211_ra_trigger_next_rateset(rn, ni);
                        return 1;
                }
                if ((rn->probing & IEEE80211_RA_PROBING_DOWN) &&
                    best_mcs > ni->ni_txmcs) {
                        ieee80211_ra_trigger_next_rateset(rn, ni);
                        return 1;
                }
        }

        /* Check if all rates in the set of candidate rates have been probed. */
        if ((rn->candidate_rates & rn->probed_rates) == rn->candidate_rates) {
                /* Remain in the current rateset until above checks trigger. */
                rn->probing &= ~IEEE80211_RA_PROBING_INTER;
                return 1;
        }

        return 0;
}

void
ieee80211_ra_trigger_next_rateset(struct ieee80211_ra_node *rn,
    struct ieee80211_node *ni)
{
        const struct ieee80211_ht_rateset *rsnext;

        rsnext = ieee80211_ra_next_rateset(rn, ni);
        if (rsnext) {
                ieee80211_ra_probe_next_rateset(rn, ni, rsnext);
                rn->probing |= IEEE80211_RA_PROBING_INTER;
        } else
                rn->probing &= ~IEEE80211_RA_PROBING_INTER;
}

int
ieee80211_ra_inter_mode_ra_finished(struct ieee80211_ra_node *rn,
    struct ieee80211_node *ni)
{
        return ((rn->probing & IEEE80211_RA_PROBING_INTER) == 0);
}

int
ieee80211_ra_best_rate(struct ieee80211_ra_node *rn,
    struct ieee80211_node *ni)
{
        int i, best = rn->best_mcs;
        uint64_t gmax = rn->g[rn->best_mcs].measured;

        for (i = 0; i < nitems(rn->g); i++) {
                struct ieee80211_ra_goodput_stats *g = &rn->g[i];
                if (((1 << i) & rn->valid_rates) == 0)
                        continue;
                if (g->measured > gmax + IEEE80211_RA_RATE_THRESHOLD) {
                        gmax = g->measured;
                        best = i;
                }
        }

#ifdef RA_DEBUG
        if (rn->best_mcs != best) {
                DPRINTF(("MCS %d is best; MCS{cur|avg|loss}:", best));
                for (i = 0; i < IEEE80211_HT_RATESET_NUM_MCS; i++) {
                        struct ieee80211_ra_goodput_stats *g = &rn->g[i];
                        if ((rn->valid_rates & (1 << i)) == 0)
                                continue;
                        DPRINTF((" %d{%s|", i, ra_fp_sprintf(g->measured)));
                        DPRINTF(("%s|", ra_fp_sprintf(g->average)));
                        DPRINTF(("%s%%}", ra_fp_sprintf(g->loss)));
                }
                DPRINTF(("\n"));
        }
#endif
        return best;
}

void
ieee80211_ra_probe_next_rate(struct ieee80211_ra_node *rn,
    struct ieee80211_node *ni)
{
        /* Select the next rate to probe. */
        rn->probed_rates |= (1 << ni->ni_txmcs);
        ni->ni_txmcs = ieee80211_ra_next_mcs(rn, ni);
}

int
ieee80211_ra_valid_tx_mcs(struct ieee80211com *ic, int mcs)
{
        uint32_t ntxstreams = 1;
        static const int max_mcs[] = { 7, 15, 23, 31 };

        if ((ic->ic_tx_mcs_set & IEEE80211_TX_RX_MCS_NOT_EQUAL) == 0)
                return isset(ic->ic_sup_mcs, mcs);

        ntxstreams += ((ic->ic_tx_mcs_set & IEEE80211_TX_SPATIAL_STREAMS) >> 2);
        if (ntxstreams < 1 || ntxstreams > 4)
                panic("invalid number of Tx streams: %u", ntxstreams);
        return (mcs <= max_mcs[ntxstreams - 1] && isset(ic->ic_sup_mcs, mcs));
}

uint32_t
ieee80211_ra_valid_rates(struct ieee80211com *ic, struct ieee80211_node *ni)
{
        uint32_t valid_mcs = 0;
        int i;

        for (i = 0; i < IEEE80211_HT_RATESET_NUM_MCS; i++) {
                if (!isset(ni->ni_rxmcs, i))
                        continue;
                if (!ieee80211_ra_valid_tx_mcs(ic, i))
                        continue;
                valid_mcs |= (1 << i);
        }

        return valid_mcs;
}

int
ieee80211_ra_probe_valid(struct ieee80211_ra_goodput_stats *g)
{
        /* 128 packets make up a valid probe in any case. */
        if (g->nprobe_pkts >= 128)
                return 1;

        /* 8 packets with > 75% loss make a valid probe, too. */
        if (g->nprobe_pkts >= 8 &&
            g->nprobe_pkts - g->nprobe_fail < g->nprobe_pkts / 4)
                return 1;

        return 0;
}

void
ieee80211_ra_add_stats_ht(struct ieee80211_ra_node *rn,
    struct ieee80211com *ic, struct ieee80211_node *ni,
    int mcs, uint32_t total, uint32_t fail)
{
        static const uint64_t alpha = RA_FP_1 / 8; /* 1/8 = 0.125 */
        static const uint64_t beta =  RA_FP_1 / 4; /* 1/4 = 0.25 */
        int s;
        struct ieee80211_ra_goodput_stats *g;
        uint64_t sfer, rate, delta;

        /*
         * Ignore invalid values. These values may come from hardware
         * so asserting valid values via panic is not appropriate.
         */
        if (mcs < 0 || mcs >= IEEE80211_HT_RATESET_NUM_MCS)
                return;
        if (total == 0)
                return;

        s = splnet();

        g = &rn->g[mcs];
        g->nprobe_pkts += total;
        g->nprobe_fail += fail;

        if (!ieee80211_ra_probe_valid(g)) {
                splx(s);
                return;
        }
        rn->valid_probes |= 1U << mcs;

        if (g->nprobe_fail > g->nprobe_pkts) {
                DPRINTF(("%s fail %u > pkts %u\n",
                    ether_sprintf(ni->ni_macaddr),
                    g->nprobe_fail, g->nprobe_pkts));
                g->nprobe_fail = g->nprobe_pkts;
        }

        sfer = g->nprobe_fail << RA_FP_SHIFT;
        sfer /= g->nprobe_pkts;
        g->nprobe_fail = 0;
        g->nprobe_pkts = 0;

        rate = ieee80211_ra_get_txrate(mcs,
            ieee80211_node_supports_ht_chan40(ni),
            ieee80211_ra_use_ht_sgi(ni));

        g->loss = sfer * 100;
        g->measured = RA_FP_MUL(RA_FP_1 - sfer, rate);
        g->average = RA_FP_MUL(RA_FP_1 - alpha, g->average);
        g->average += RA_FP_MUL(alpha, g->measured);

        g->stddeviation = RA_FP_MUL(RA_FP_1 - beta, g->stddeviation);
        if (g->average > g->measured)
                delta = g->average - g->measured;
        else
                delta = g->measured - g->average;
        g->stddeviation += RA_FP_MUL(beta, delta);

        splx(s);
}

void
ieee80211_ra_choose(struct ieee80211_ra_node *rn, struct ieee80211com *ic,
    struct ieee80211_node *ni)
{
        struct ieee80211_ra_goodput_stats *g = &rn->g[ni->ni_txmcs];
        int s;
        int chan40 = ieee80211_node_supports_ht_chan40(ni);
        int sgi = ieee80211_ra_use_ht_sgi(ni);
        const struct ieee80211_ht_rateset *rs, *rsnext;

        s = splnet();

        if (rn->valid_rates == 0)
                rn->valid_rates = ieee80211_ra_valid_rates(ic, ni);

        if (rn->probing) {
                /* Probe another rate or settle at the best rate. */
                if (!(rn->valid_probes & (1UL << ni->ni_txmcs))) {
                        splx(s);
                        return;
                }
                ieee80211_ra_probe_clear(rn, ni);
                if (!ieee80211_ra_intra_mode_ra_finished(rn, ni)) {
                        ieee80211_ra_probe_next_rate(rn, ni);
                        DPRINTFN(3, ("probing MCS %d\n", ni->ni_txmcs));
                } else if (ieee80211_ra_inter_mode_ra_finished(rn, ni)) {
                        rn->best_mcs = ieee80211_ra_best_rate(rn, ni);
                        ni->ni_txmcs = rn->best_mcs;
                        ieee80211_ra_probe_done(rn);
                }

                splx(s);
                return;
        } else {
                rn->valid_probes = 0;
        }

        rs = ieee80211_ra_get_ht_rateset(ni->ni_txmcs, chan40, sgi);
        if ((g->measured >> RA_FP_SHIFT) == 0LL ||
            (g->average >= 3 * g->stddeviation &&
            g->measured < g->average - 3 * g->stddeviation)) {
                /* Channel becomes bad. Probe downwards. */
                rn->probing = IEEE80211_RA_PROBING_DOWN;
                rn->probed_rates = 0;
                if (ni->ni_txmcs == rs->min_mcs) {
                        rsnext = ieee80211_ra_next_rateset(rn, ni);
                        if (rsnext) {
                                ieee80211_ra_probe_next_rateset(rn, ni,
                                    rsnext);
                        } else {
                                /* Cannot probe further down. */
                                rn->probing = IEEE80211_RA_NOT_PROBING;
                        }
                } else {
                        ni->ni_txmcs = ieee80211_ra_next_mcs(rn, ni);
                        rn->candidate_rates = (1 << ni->ni_txmcs);
                }
        } else if (g->loss < 2 * RA_FP_1 ||
            g->measured > g->average + 3 * g->stddeviation) {
                /* Channel becomes good. */
                rn->probing = IEEE80211_RA_PROBING_UP;
                rn->probed_rates = 0;
                if (ni->ni_txmcs == rs->max_mcs) {
                        rsnext = ieee80211_ra_next_rateset(rn, ni);
                        if (rsnext) {
                                ieee80211_ra_probe_next_rateset(rn, ni,
                                    rsnext);
                        } else {
                                /* Cannot probe further up. */
                                rn->probing = IEEE80211_RA_NOT_PROBING;
                        }
                } else {
                        ni->ni_txmcs = ieee80211_ra_next_mcs(rn, ni);
                        rn->candidate_rates = (1 << ni->ni_txmcs);
                }
        } else {
                /* Remain at current rate. */
                rn->probing = IEEE80211_RA_NOT_PROBING;
                rn->probed_rates = 0;
                rn->candidate_rates = 0;
        }

        splx(s);

        if (rn->probing) {
                if (rn->probing & IEEE80211_RA_PROBING_UP)
                        DPRINTFN(2, ("channel becomes good; probe up\n"));
                else
                        DPRINTFN(2, ("channel becomes bad; probe down\n"));

                DPRINTFN(3, ("measured: %s Mbit/s\n",
                    ra_fp_sprintf(g->measured)));
                DPRINTFN(3, ("average: %s Mbit/s\n",
                    ra_fp_sprintf(g->average)));
                DPRINTFN(3, ("stddeviation: %s\n",
                    ra_fp_sprintf(g->stddeviation)));
                DPRINTFN(3, ("loss: %s%%\n", ra_fp_sprintf(g->loss)));
        }
}

void
ieee80211_ra_node_init(struct ieee80211_ra_node *rn)
{
        memset(rn, 0, sizeof(*rn));
}