/*

 * Copyright © 2018, VideoLAN and dav1d authors

 * Copyright © 2018, Two Orioles, LLC

 * All rights reserved.

 *

 * Redistribution and use in source and binary forms, with or without

 * modification, are permitted provided that the following conditions are met:

 *

 * 1. Redistributions of source code must retain the above copyright notice, this

 *    list of conditions and the following disclaimer.

 *

 * 2. Redistributions in binary form must reproduce the above copyright notice,

 *    this list of conditions and the following disclaimer in the documentation

 *    and/or other materials provided with the distribution.

 *

 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND

 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED

 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE

 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR

 * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES

 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;

 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND

 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT

 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS

 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

 */

#include "config.h"

#include <limits.h>

#include "common/intops.h"

#include "src/msac.h"

#define EC_PROB_SHIFT 6

#define EC_MIN_PROB 4  // must be <= (1<<EC_PROB_SHIFT)/16

#define EC_WIN_SIZE (sizeof(ec_win) << 3)

static inline void ctx_refill(MsacContext *const s) {

    const uint8_t *buf_pos = s->buf_pos;

    const uint8_t *buf_end = s->buf_end;

    int c = EC_WIN_SIZE - s->cnt - 24;

    ec_win dif = s->dif;

    do {

        if (buf_pos >= buf_end) {

            // set remaining bits to 1;

            dif |= ~(~(ec_win)0xff << c);

            break;

        }

        dif |= (ec_win)(*buf_pos++ ^ 0xff) << c;

        c -= 8;

    } while (c >= 0);

    s->dif = dif;

    s->cnt = EC_WIN_SIZE - c - 24;

    s->buf_pos = buf_pos;

}

int dav1d_msac_decode_subexp(MsacContext *const s, const int ref,

                             const int n, unsigned k)

{

    assert(n >> k == 8);

    unsigned a = 0;

    if (dav1d_msac_decode_bool_equi(s)) {

        if (dav1d_msac_decode_bool_equi(s))

            k += dav1d_msac_decode_bool_equi(s) + 1;

        a = 1 << k;

    }

    const unsigned v = dav1d_msac_decode_bools(s, k) + a;

    return ref * 2 <= n ? inv_recenter(ref, v) :

                          n - 1 - inv_recenter(n - 1 - ref, v);

}

#if !(HAVE_ASM && TRIM_DSP_FUNCTIONS && ( \

  ARCH_AARCH64 || \

  (ARCH_ARM && (defined(__ARM_NEON) || defined(__APPLE__) || defined(_WIN32))) \

))

/* Takes updated dif and range values, renormalizes them so that

 * 32768 <= rng < 65536 (reading more bytes from the stream into dif if

 * necessary), and stores them back in the decoder context.

 * dif: The new value of dif.

 * rng: The new value of the range. */

static inline void ctx_norm(MsacContext *const s, const ec_win dif,

                            const unsigned rng)

{

    const int d = 15 ^ (31 ^ clz(rng));

    const int cnt = s->cnt;

    assert(rng <= 65535U);

    s->dif = dif << d;

    s->rng = rng << d;

    s->cnt = cnt - d;

    // unsigned compare avoids redundant refills at eob

    if ((unsigned)cnt < (unsigned)d)

        ctx_refill(s);

}

unsigned dav1d_msac_decode_bool_equi_c(MsacContext *const s) {

    const unsigned r = s->rng;

    ec_win dif = s->dif;

    assert((dif >> (EC_WIN_SIZE - 16)) < r);

    // When the probability is 1/2, f = 16384 >> EC_PROB_SHIFT = 256 and we can

    // replace the multiply with a simple shift.

    unsigned v = ((r >> 8) << 7) + EC_MIN_PROB;

    const ec_win vw = (ec_win)v << (EC_WIN_SIZE - 16);

    const unsigned ret = dif >= vw;

    dif -= ret * vw;

    v += ret * (r - 2 * v);

    ctx_norm(s, dif, v);

    return !ret;

}

/* Decode a single binary value.

 * f: The probability that the bit is one

 * Return: The value decoded (0 or 1). */

unsigned dav1d_msac_decode_bool_c(MsacContext *const s, const unsigned f) {

    const unsigned r = s->rng;

    ec_win dif = s->dif;

    assert((dif >> (EC_WIN_SIZE - 16)) < r);

    unsigned v = ((r >> 8) * (f >> EC_PROB_SHIFT) >> (7 - EC_PROB_SHIFT)) + EC_MIN_PROB;

    const ec_win vw = (ec_win)v << (EC_WIN_SIZE - 16);

    const unsigned ret = dif >= vw;

    dif -= ret * vw;

    v += ret * (r - 2 * v);

    ctx_norm(s, dif, v);

    return !ret;

}

/* Decodes a symbol given an inverse cumulative distribution function (CDF)

 * table in Q15. */

unsigned dav1d_msac_decode_symbol_adapt_c(MsacContext *const s,

                                          uint16_t *const cdf,

                                          const size_t n_symbols)

{

    const unsigned c = s->dif >> (EC_WIN_SIZE - 16), r = s->rng >> 8;

    unsigned u, v = s->rng, val = -1;

    assert(n_symbols <= 15);

    assert(cdf[n_symbols] <= 32);

    do {

        val++;

        u = v;

        v = r * (cdf[val] >> EC_PROB_SHIFT);

        v >>= 7 - EC_PROB_SHIFT;

        v += EC_MIN_PROB * ((unsigned)n_symbols - val);

    } while (c < v);

    assert(u <= s->rng);

    ctx_norm(s, s->dif - ((ec_win)v << (EC_WIN_SIZE - 16)), u - v);

    if (s->allow_update_cdf) {

        const unsigned count = cdf[n_symbols];

        const unsigned rate = 4 + (count >> 4) + (n_symbols > 2);

        unsigned i;

        for (i = 0; i < val; i++)

            cdf[i] += (32768 - cdf[i]) >> rate;

        for (; i < n_symbols; i++)

            cdf[i] -= cdf[i] >> rate;

        cdf[n_symbols] = count + (count < 32);

    }

    return val;

}

unsigned dav1d_msac_decode_bool_adapt_c(MsacContext *const s,

                                        uint16_t *const cdf)

{

    const unsigned bit = dav1d_msac_decode_bool(s, *cdf);

    if (s->allow_update_cdf) {

        // update_cdf() specialized for boolean CDFs

        const unsigned count = cdf[1];

        const int rate = 4 + (count >> 4);

        if (bit)

            cdf[0] += (32768 - cdf[0]) >> rate;

        else

            cdf[0] -= cdf[0] >> rate;

        cdf[1] = count + (count < 32);

    }

    return bit;

}

unsigned dav1d_msac_decode_hi_tok_c(MsacContext *const s, uint16_t *const cdf) {

    unsigned tok_br = dav1d_msac_decode_symbol_adapt4(s, cdf, 3);

    unsigned tok = 3 + tok_br;

    if (tok_br == 3) {

        tok_br = dav1d_msac_decode_symbol_adapt4(s, cdf, 3);

        tok = 6 + tok_br;

        if (tok_br == 3) {

            tok_br = dav1d_msac_decode_symbol_adapt4(s, cdf, 3);

            tok = 9 + tok_br;

            if (tok_br == 3)

                tok = 12 + dav1d_msac_decode_symbol_adapt4(s, cdf, 3);

        }

    }

    return tok;

}

#endif

void dav1d_msac_init(MsacContext *const s, const uint8_t *const data,

                     const size_t sz, const int disable_cdf_update_flag)

{

    s->buf_pos = data;

    s->buf_end = data + sz;

    s->dif = 0;

    s->rng = 0x8000;

    s->cnt = -15;

    s->allow_update_cdf = !disable_cdf_update_flag;

    ctx_refill(s);

#if ARCH_X86_64 && HAVE_ASM

    s->symbol_adapt16 = dav1d_msac_decode_symbol_adapt_c;

    msac_init_x86(s);

#endif

}