/* Copyright (c) 2001-2011 Timothy B. Terriberry

*/

/*

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

   modification, are permitted provided that the following conditions

   are met:

   - Redistributions of source code must retain the above copyright

   notice, this list of conditions and the following disclaimer.

   - 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.

*/

#ifdef HAVE_CONFIG_H

#include "config.h"

#endif

#include "entcode.h"

#include "arch.h"

#if !defined(EC_CLZ)

/*This is a fallback for systems where we don't know how to access

   a BSR or CLZ instruction (see ecintrin.h).

  If you are optimizing Opus on a new platform and it has a native CLZ or

   BZR (e.g. cell, MIPS, x86, etc) then making it available to Opus will be

   an easy performance win.*/

int ec_ilog(opus_uint32 _v){

  /*On a Pentium M, this branchless version tested as the fastest on

     1,000,000,000 random 32-bit integers, edging out a similar version with

     branches, and a 256-entry LUT version.*/

  int ret;

  int m;

  ret=!!_v;

  m=!!(_v&0xFFFF0000)<<4;

  _v>>=m;

  ret|=m;

  m=!!(_v&0xFF00)<<3;

  _v>>=m;

  ret|=m;

  m=!!(_v&0xF0)<<2;

  _v>>=m;

  ret|=m;

  m=!!(_v&0xC)<<1;

  _v>>=m;

  ret|=m;

  ret+=!!(_v&0x2);

  return ret;

}

#endif

#if 1

/* This is a faster version of ec_tell_frac() that takes advantage

   of the low (1/8 bit) resolution to use just a linear function

   followed by a lookup to determine the exact transition thresholds. */

opus_uint32 ec_tell_frac(ec_ctx *_this){

  static const unsigned correction[8] =

    {35733, 38967, 42495, 46340,

     50535, 55109, 60097, 65535};

  opus_uint32 nbits;

  opus_uint32 r;

  int         l;

  unsigned    b;

  nbits=_this->nbits_total<<BITRES;

  l=EC_ILOG(_this->rng);

  r=_this->rng>>(l-16);

  b = (r>>12)-8;

  b += r>correction[b];

  l = (l<<3)+b;

  return nbits-l;

}

#else

opus_uint32 ec_tell_frac(ec_ctx *_this){

  opus_uint32 nbits;

  opus_uint32 r;

  int         l;

  int         i;

  /*To handle the non-integral number of bits still left in the encoder/decoder

     state, we compute the worst-case number of bits of val that must be

     encoded to ensure that the value is inside the range for any possible

     subsequent bits.

    The computation here is independent of val itself (the decoder does not

     even track that value), even though the real number of bits used after

     ec_enc_done() may be 1 smaller if rng is a power of two and the

     corresponding trailing bits of val are all zeros.

    If we did try to track that special case, then coding a value with a

     probability of 1/(1<<n) might sometimes appear to use more than n bits.

    This may help explain the surprising result that a newly initialized

     encoder or decoder claims to have used 1 bit.*/

  nbits=_this->nbits_total<<BITRES;

  l=EC_ILOG(_this->rng);

  r=_this->rng>>(l-16);

  for(i=BITRES;i-->0;){

    int b;

    r=r*r>>15;

    b=(int)(r>>16);

    l=l<<1|b;

    r>>=b;

  }

  return nbits-l;

}

#endif

#ifdef USE_SMALL_DIV_TABLE

/* Result of 2^32/(2*i+1), except for i=0. */

const opus_uint32 SMALL_DIV_TABLE[129] = {

   0xFFFFFFFF, 0x55555555, 0x33333333, 0x24924924,

   0x1C71C71C, 0x1745D174, 0x13B13B13, 0x11111111,

   0x0F0F0F0F, 0x0D79435E, 0x0C30C30C, 0x0B21642C,

   0x0A3D70A3, 0x097B425E, 0x08D3DCB0, 0x08421084,

   0x07C1F07C, 0x07507507, 0x06EB3E45, 0x06906906,

   0x063E7063, 0x05F417D0, 0x05B05B05, 0x0572620A,

   0x05397829, 0x05050505, 0x04D4873E, 0x04A7904A,

   0x047DC11F, 0x0456C797, 0x04325C53, 0x04104104,

   0x03F03F03, 0x03D22635, 0x03B5CC0E, 0x039B0AD1,

   0x0381C0E0, 0x0369D036, 0x03531DEC, 0x033D91D2,

   0x0329161F, 0x03159721, 0x03030303, 0x02F14990,

   0x02E05C0B, 0x02D02D02, 0x02C0B02C, 0x02B1DA46,

   0x02A3A0FD, 0x0295FAD4, 0x0288DF0C, 0x027C4597,

   0x02702702, 0x02647C69, 0x02593F69, 0x024E6A17,

   0x0243F6F0, 0x0239E0D5, 0x02302302, 0x0226B902,

   0x021D9EAD, 0x0214D021, 0x020C49BA, 0x02040810,

   0x01FC07F0, 0x01F44659, 0x01ECC07B, 0x01E573AC,

   0x01DE5D6E, 0x01D77B65, 0x01D0CB58, 0x01CA4B30,

   0x01C3F8F0, 0x01BDD2B8, 0x01B7D6C3, 0x01B20364,

   0x01AC5701, 0x01A6D01A, 0x01A16D3F, 0x019C2D14,

   0x01970E4F, 0x01920FB4, 0x018D3018, 0x01886E5F,

   0x0183C977, 0x017F405F, 0x017AD220, 0x01767DCE,

   0x01724287, 0x016E1F76, 0x016A13CD, 0x01661EC6,

   0x01623FA7, 0x015E75BB, 0x015AC056, 0x01571ED3,

   0x01539094, 0x01501501, 0x014CAB88, 0x0149539E,

   0x01460CBC, 0x0142D662, 0x013FB013, 0x013C995A,

   0x013991C2, 0x013698DF, 0x0133AE45, 0x0130D190,

   0x012E025C, 0x012B404A, 0x01288B01, 0x0125E227,

   0x01234567, 0x0120B470, 0x011E2EF3, 0x011BB4A4,

   0x01194538, 0x0116E068, 0x011485F0, 0x0112358E,

   0x010FEF01, 0x010DB20A, 0x010B7E6E, 0x010953F3,

   0x01073260, 0x0105197F, 0x0103091B, 0x01010101

};

#endif