vp8/encoder/encodemv.c

/*
 *  Copyright (c) 2010 The WebM project authors. All Rights Reserved.
 *
 *  Use of this source code is governed by a BSD-style license
 *  that can be found in the LICENSE file in the root of the source
 *  tree. An additional intellectual property rights grant can be found
 *  in the file PATENTS.  All contributing project authors may
 *  be found in the AUTHORS file in the root of the source tree.
 */


#include "vp8/common/common.h"
#include "encodemv.h"
#include "vp8/common/entropymode.h"
#include "vp8/common/systemdependent.h"

#include <math.h>

#ifdef VP8_ENTROPY_STATS
extern unsigned int active_section;
#endif

static void encode_mvcomponent(
    vp8_writer *const w,
    const int v,
    const struct mv_context *mvc
)
{
    const vp8_prob *p = mvc->prob;
    const int x = v < 0 ? -v : v;

    if (x < mvnum_short)     /* Small */
    {
        vp8_write(w, 0, p [mvpis_short]);
        vp8_treed_write(w, vp8_small_mvtree, p + MVPshort, x, 3);

        if (!x)
            return;         /* no sign bit */
    }
    else                    /* Large */
    {
        int i = 0;

        vp8_write(w, 1, p [mvpis_short]);

        do
            vp8_write(w, (x >> i) & 1, p [MVPbits + i]);

        while (++i < 3);

        i = mvlong_width - 1;  /* Skip bit 3, which is sometimes implicit */

        do
            vp8_write(w, (x >> i) & 1, p [MVPbits + i]);

        while (--i > 3);

        if (x & 0xFFF0)
            vp8_write(w, (x >> 3) & 1, p [MVPbits + 3]);
    }

    vp8_write(w, v < 0, p [MVPsign]);
}
#if 0
static int max_mv_r = 0;
static int max_mv_c = 0;
#endif
void vp8_encode_motion_vector(vp8_writer *w, const MV *mv, const MV_CONTEXT *mvc)
{

#if 0
    {
        if (abs(mv->row >> 1) > max_mv_r)
        {
            FILE *f = fopen("maxmv.stt", "a");
            max_mv_r = abs(mv->row >> 1);
            fprintf(f, "New Mv Row Max %6d\n", (mv->row >> 1));

            if ((abs(mv->row) / 2) != max_mv_r)
                fprintf(f, "MV Row conversion error %6d\n", abs(mv->row) / 2);

            fclose(f);
        }

        if (abs(mv->col >> 1) > max_mv_c)
        {
            FILE *f = fopen("maxmv.stt", "a");
            fprintf(f, "New Mv Col Max %6d\n", (mv->col >> 1));
            max_mv_c = abs(mv->col >> 1);
            fclose(f);
        }
    }
#endif

    encode_mvcomponent(w, mv->row >> 1, &mvc[0]);
    encode_mvcomponent(w, mv->col >> 1, &mvc[1]);
}


static unsigned int cost_mvcomponent(const int v, const struct mv_context *mvc)
{
    const vp8_prob *p = mvc->prob;
    const int x = v;
    unsigned int cost;

    if (x < mvnum_short)
    {
        cost = vp8_cost_zero(p [mvpis_short])
               + vp8_treed_cost(vp8_small_mvtree, p + MVPshort, x, 3);

        if (!x)
            return cost;
    }
    else
    {
        int i = 0;
        cost = vp8_cost_one(p [mvpis_short]);

        do
            cost += vp8_cost_bit(p [MVPbits + i], (x >> i) & 1);

        while (++i < 3);

        i = mvlong_width - 1;  /* Skip bit 3, which is sometimes implicit */

        do
            cost += vp8_cost_bit(p [MVPbits + i], (x >> i) & 1);

        while (--i > 3);

        if (x & 0xFFF0)
            cost += vp8_cost_bit(p [MVPbits + 3], (x >> 3) & 1);
    }

    return cost;   /* + vp8_cost_bit( p [MVPsign], v < 0); */
}

void vp8_build_component_cost_table(int *mvcost[2], const MV_CONTEXT *mvc, int mvc_flag[2])
{
    int i = 1;
    unsigned int cost0 = 0;
    unsigned int cost1 = 0;

    vp8_clear_system_state();

    i = 1;

    if (mvc_flag[0])
    {
        mvcost [0] [0] = cost_mvcomponent(0, &mvc[0]);

        do
        {
            cost0 = cost_mvcomponent(i, &mvc[0]);

            mvcost [0] [i] = cost0 + vp8_cost_zero(mvc[0].prob[MVPsign]);
            mvcost [0] [-i] = cost0 + vp8_cost_one(mvc[0].prob[MVPsign]);
        }
        while (++i <= mv_max);
    }

    i = 1;

    if (mvc_flag[1])
    {
        mvcost [1] [0] = cost_mvcomponent(0, &mvc[1]);

        do
        {
            cost1 = cost_mvcomponent(i, &mvc[1]);

            mvcost [1] [i] = cost1 + vp8_cost_zero(mvc[1].prob[MVPsign]);
            mvcost [1] [-i] = cost1 + vp8_cost_one(mvc[1].prob[MVPsign]);
        }
        while (++i <= mv_max);
    }
}


/* Motion vector probability table update depends on benefit.
 * Small correction allows for the fact that an update to an MV probability
 * may have benefit in subsequent frames as well as the current one.
 */
#define MV_PROB_UPDATE_CORRECTION   -1


static void calc_prob(vp8_prob *p, const unsigned int ct[2])
{
    const unsigned int tot = ct[0] + ct[1];

    if (tot)
    {
        const vp8_prob x = ((ct[0] * 255) / tot) & -2;
        *p = x ? x : 1;
    }
}

static void update(
    vp8_writer *const w,
    const unsigned int ct[2],
    vp8_prob *const cur_p,
    const vp8_prob new_p,
    const vp8_prob update_p,
    int *updated
)
{
    const int cur_b = vp8_cost_branch(ct, *cur_p);
    const int new_b = vp8_cost_branch(ct, new_p);
    const int cost = 7 + MV_PROB_UPDATE_CORRECTION + ((vp8_cost_one(update_p) - vp8_cost_zero(update_p) + 128) >> 8);

    if (cur_b - new_b > cost)
    {
        *cur_p = new_p;
        vp8_write(w, 1, update_p);
        vp8_write_literal(w, new_p >> 1, 7);
        *updated = 1;

    }
    else
        vp8_write(w, 0, update_p);
}

static void write_component_probs(
    vp8_writer *const w,
    struct mv_context *cur_mvc,
    const struct mv_context *default_mvc_,
    const struct mv_context *update_mvc,
    const unsigned int events [MVvals],
    unsigned int rc,
    int *updated
)
{
    vp8_prob *Pcur = cur_mvc->prob;
    const vp8_prob *default_mvc = default_mvc_->prob;
    const vp8_prob *Pupdate = update_mvc->prob;
    unsigned int is_short_ct[2], sign_ct[2];

    unsigned int bit_ct [mvlong_width] [2];

    unsigned int short_ct  [mvnum_short];
    unsigned int short_bct [mvnum_short-1] [2];

    vp8_prob Pnew [MVPcount];

    (void) rc;
    vp8_copy_array(Pnew, default_mvc, MVPcount);

    vp8_zero(is_short_ct)
    vp8_zero(sign_ct)
    vp8_zero(bit_ct)
    vp8_zero(short_ct)
    vp8_zero(short_bct)


    /* j=0 */
    {
        const int c = events [mv_max];

        is_short_ct [0] += c;     /* Short vector */
        short_ct [0] += c;       /* Magnitude distribution */
    }

    /* j: 1 ~ mv_max (1023) */
    {
        int j = 1;

        do
        {
            const int c1 = events [mv_max + j];  /* positive */
            const int c2 = events [mv_max - j];  /* negative */
            const int c  = c1 + c2;
            int a = j;

            sign_ct [0] += c1;
            sign_ct [1] += c2;

            if (a < mvnum_short)
            {
                is_short_ct [0] += c;     /* Short vector */
                short_ct [a] += c;       /* Magnitude distribution */
            }
            else
            {
                int k = mvlong_width - 1;
                is_short_ct [1] += c;     /* Long vector */

                /*  bit 3 not always encoded. */
                do
                    bit_ct [k] [(a >> k) & 1] += c;

                while (--k >= 0);
            }
        }
        while (++j <= mv_max);
    }

    calc_prob(Pnew + mvpis_short, is_short_ct);

    calc_prob(Pnew + MVPsign, sign_ct);

    {
        vp8_prob p [mvnum_short - 1];    /* actually only need branch ct */
        int j = 0;

        vp8_tree_probs_from_distribution(
            8, vp8_small_mvencodings, vp8_small_mvtree,
            p, short_bct, short_ct,
            256, 1
        );

        do
            calc_prob(Pnew + MVPshort + j, short_bct[j]);

        while (++j < mvnum_short - 1);
    }

    {
        int j = 0;

        do
            calc_prob(Pnew + MVPbits + j, bit_ct[j]);

        while (++j < mvlong_width);
    }

    update(w, is_short_ct, Pcur + mvpis_short, Pnew[mvpis_short], *Pupdate++, updated);

    update(w, sign_ct, Pcur + MVPsign, Pnew[MVPsign], *Pupdate++, updated);

    {
        const vp8_prob *const new_p = Pnew + MVPshort;
        vp8_prob *const cur_p = Pcur + MVPshort;

        int j = 0;

        do

            update(w, short_bct[j], cur_p + j, new_p[j], *Pupdate++, updated);

        while (++j < mvnum_short - 1);
    }

    {
        const vp8_prob *const new_p = Pnew + MVPbits;
        vp8_prob *const cur_p = Pcur + MVPbits;

        int j = 0;

        do

            update(w, bit_ct[j], cur_p + j, new_p[j], *Pupdate++, updated);

        while (++j < mvlong_width);
    }
}

void vp8_write_mvprobs(VP8_COMP *cpi)
{
    vp8_writer *const w  = cpi->bc;
    MV_CONTEXT *mvc = cpi->common.fc.mvc;
    int flags[2] = {0, 0};
#ifdef VP8_ENTROPY_STATS
    active_section = 4;
#endif
    write_component_probs(
        w, &mvc[0], &vp8_default_mv_context[0], &vp8_mv_update_probs[0],
        cpi->mb.MVcount[0], 0, &flags[0]
    );
    write_component_probs(
        w, &mvc[1], &vp8_default_mv_context[1], &vp8_mv_update_probs[1],
        cpi->mb.MVcount[1], 1, &flags[1]
    );

    if (flags[0] || flags[1])
        vp8_build_component_cost_table(cpi->mb.mvcost, (const MV_CONTEXT *) cpi->common.fc.mvc, flags);

#ifdef VP8_ENTROPY_STATS
    active_section = 5;
#endif
}