vp8/decoder/dboolhuff.h

/*
 *  Copyright (c) 2010 The VP8 project authors. All Rights Reserved.
 *
 *  Use of this source code is governed by a BSD-style license and patent
 *  grant that can be found in the LICENSE file in the root of the source
 *  tree. All contributing project authors may be found in the AUTHORS
 *  file in the root of the source tree.
 */


#ifndef DBOOLHUFF_H
#define DBOOLHUFF_H
#include "vpx_ports/config.h"
#include "vpx_ports/mem.h"
#include "vpx_ports/vpx_integer.h"

/* Size of the bool decoder backing storage
 *
 * This size was chosen to be greater than the worst case encoding of a
 * single macroblock. This was calcluated as follows (python):
 *
 *     def max_cost(prob):
 *         return max(prob_costs[prob], prob_costs[255-prob]) / 256;
 *
 *     tree_nodes_cost = 7 * max_cost(255)
 *     extra_bits_cost = sum([max_cost(bit) for bit in extra_bits])
 *     sign_bit_cost = max_cost(128)
 *     total_cost = tree_nodes_cost + extra_bits_cost + sign_bit_cost
 *
 * where the prob_costs table was taken from the C vp8_prob_cost table in
 * boolhuff.c and the extra_bits table was taken from the 11 extrabits for
 * a category 6 token as defined in vp8d_token_extra_bits2/detokenize.c
 *
 * This equation produced a maximum of 79 bits per coefficient. Scaling up
 * to the macroblock level:
 *
 *     79 bits/coeff * 16 coeff/block * 25 blocks/macroblock = 31600 b/mb
 *
 *     4096 bytes = 32768 bits > 31600
 */
#define VP8_BOOL_DECODER_SZ       4096
#define VP8_BOOL_DECODER_MASK     (VP8_BOOL_DECODER_SZ-1)
#define VP8_BOOL_DECODER_PTR_MASK (~(uintptr_t)(VP8_BOOL_DECODER_SZ))

struct vp8_dboolhuff_rtcd_vtable;

typedef struct
{
    unsigned int         lowvalue;
    unsigned int         range;
    unsigned int         value;
    int                  count;
    const unsigned char *user_buffer;
    unsigned int         user_buffer_sz;
    unsigned char       *decode_buffer;
    const unsigned char *read_ptr;
    unsigned char       *write_ptr;
#if CONFIG_RUNTIME_CPU_DETECT
    struct vp8_dboolhuff_rtcd_vtable *rtcd;
#endif
} BOOL_DECODER;

#define prototype_dbool_start(sym) int sym(BOOL_DECODER *br, \
    const unsigned char *source, unsigned int source_sz)
#define prototype_dbool_stop(sym) void sym(BOOL_DECODER *bc)
#define prototype_dbool_fill(sym) void sym(BOOL_DECODER *br)
#define prototype_dbool_debool(sym) int sym(BOOL_DECODER *br, int probability)
#define prototype_dbool_devalue(sym) int sym(BOOL_DECODER *br, int bits);

#if ARCH_ARM
#include "arm/dboolhuff_arm.h"
#endif

#ifndef vp8_dbool_start
#define vp8_dbool_start vp8dx_start_decode_c
#endif

#ifndef vp8_dbool_stop
#define vp8_dbool_stop vp8dx_stop_decode_c
#endif

#ifndef vp8_dbool_fill
#define vp8_dbool_fill vp8dx_bool_decoder_fill_c
#endif

#ifndef vp8_dbool_debool
#define vp8_dbool_debool vp8dx_decode_bool_c
#endif

#ifndef vp8_dbool_devalue
#define vp8_dbool_devalue vp8dx_decode_value_c
#endif

extern prototype_dbool_start(vp8_dbool_start);
extern prototype_dbool_stop(vp8_dbool_stop);
extern prototype_dbool_fill(vp8_dbool_fill);
extern prototype_dbool_debool(vp8_dbool_debool);
extern prototype_dbool_devalue(vp8_dbool_devalue);

typedef prototype_dbool_start((*vp8_dbool_start_fn_t));
typedef prototype_dbool_stop((*vp8_dbool_stop_fn_t));
typedef prototype_dbool_fill((*vp8_dbool_fill_fn_t));
typedef prototype_dbool_debool((*vp8_dbool_debool_fn_t));
typedef prototype_dbool_devalue((*vp8_dbool_devalue_fn_t));

typedef struct vp8_dboolhuff_rtcd_vtable {
    vp8_dbool_start_fn_t   start;
    vp8_dbool_stop_fn_t    stop;
    vp8_dbool_fill_fn_t    fill;
    vp8_dbool_debool_fn_t  debool;
    vp8_dbool_devalue_fn_t devalue;
} vp8_dboolhuff_rtcd_vtable_t;

// There are no processor-specific versions of these
// functions right now. Disable RTCD to avoid using
// function pointers which gives a speed boost
//#ifdef ENABLE_RUNTIME_CPU_DETECT
//#define DBOOLHUFF_INVOKE(ctx,fn) (ctx)->fn
//#define IF_RTCD(x) (x)
//#else
#define DBOOLHUFF_INVOKE(ctx,fn) vp8_dbool_##fn
#define IF_RTCD(x) NULL
//#endif

static unsigned char *br_ptr_advance(const unsigned char *_ptr,
                                     unsigned int n)
{
    uintptr_t  ptr = (uintptr_t)_ptr;

    ptr += n;
    ptr &= VP8_BOOL_DECODER_PTR_MASK;

    return (void *)ptr;
}

DECLARE_ALIGNED(16, extern const unsigned int, vp8dx_bitreader_norm[256]);

/* wrapper functions to hide RTCD. static means inline means hopefully no
 * penalty
 */
static int vp8dx_start_decode(BOOL_DECODER *br,
        struct vp8_dboolhuff_rtcd_vtable *rtcd,
        const unsigned char *source, unsigned int source_sz) {
#if CONFIG_RUNTIME_CPU_DETECT
    br->rtcd = rtcd;
#endif
    return DBOOLHUFF_INVOKE(rtcd, start)(br, source, source_sz);
}
static void vp8dx_stop_decode(BOOL_DECODER *br) {
    DBOOLHUFF_INVOKE(br->rtcd, stop)(br);
}
static void vp8dx_bool_decoder_fill(BOOL_DECODER *br) {
    DBOOLHUFF_INVOKE(br->rtcd, fill)(br);
}
static int vp8dx_decode_bool(BOOL_DECODER *br, int probability) {
  /*
   * Until optimized versions of this function are available, we
   * keep the implementation in the header to allow inlining.
   *
   *return DBOOLHUFF_INVOKE(br->rtcd, debool)(br, probability);
   */
    unsigned int bit = 0;
    unsigned int split;
    unsigned int bigsplit;
    register unsigned int range = br->range;
    register unsigned int value = br->value;

    split = 1 + (((range - 1) * probability) >> 8);
    bigsplit = (split << 8);

    range = split;

    if (value >= bigsplit)
    {
        range = br->range - split;
        value = value - bigsplit;
        bit = 1;
    }

    /*if(range>=0x80)
    {
        br->value = value;
        br->range = range;
        return bit
    }*/

    {
        int count = br->count;
        register unsigned int shift = vp8dx_bitreader_norm[range];
        range <<= shift;
        value <<= shift;
        count -= shift;

        if (count <= 0)
        {
            value |= (*br->read_ptr) << (-count);
            br->read_ptr = br_ptr_advance(br->read_ptr, 1);
            count += 8 ;
        }

        br->count = count;
    }
    br->value = value;
    br->range = range;
    return bit;
}

static int vp8_decode_value(BOOL_DECODER *br, int bits)
{
  /*
   * Until optimized versions of this function are available, we
   * keep the implementation in the header to allow inlining.
   *
   *return DBOOLHUFF_INVOKE(br->rtcd, devalue)(br, bits);
   */
    int z = 0;
    int bit;

    for (bit = bits - 1; bit >= 0; bit--)
    {
        z |= (vp8dx_decode_bool(br, 0x80) << bit);
    }

    return z;
}
#endif