snow.c

ffmpeg的完整源代码和作者自己写的文档。不但有在Linux的工程哦

            e++;
        }

        a= 1;
        for(i=e-1; i>=0; i--){
            a += a + get_rac(c, state+22 + FFMIN(i,9)); //22..31
        }

        if(is_signed && get_rac(c, state+11 + FFMIN(e,10))) //11..21
            return -a;
        else
            return a;
    }
}

static inline void put_symbol2(RangeCoder *c, uint8_t *state, int v, int log2){
    int i;
    int r= log2>=0 ? 1<<log2 : 1;

    assert(v>=0);
    assert(log2>=-4);

    while(v >= r){
        put_rac(c, state+4+log2, 1);
        v -= r;
        log2++;
        if(log2>0) r+=r;
    }
    put_rac(c, state+4+log2, 0);

    for(i=log2-1; i>=0; i--){
        put_rac(c, state+31-i, (v>>i)&1);
    }
}

static inline int get_symbol2(RangeCoder *c, uint8_t *state, int log2){
    int i;
    int r= log2>=0 ? 1<<log2 : 1;
    int v=0;

    assert(log2>=-4);

    while(get_rac(c, state+4+log2)){
        v+= r;
        log2++;
        if(log2>0) r+=r;
    }

    for(i=log2-1; i>=0; i--){
        v+= get_rac(c, state+31-i)<<i;
    }

    return v;
}

static av_always_inline void
lift(DWTELEM *dst, DWTELEM *src, DWTELEM *ref,
     int dst_step, int src_step, int ref_step,
     int width, int mul, int add, int shift,
     int highpass, int inverse){
    const int mirror_left= !highpass;
    const int mirror_right= (width&1) ^ highpass;
    const int w= (width>>1) - 1 + (highpass & width);
    int i;

#define LIFT(src, ref, inv) ((src) + ((inv) ? - (ref) : + (ref)))
    if(mirror_left){
        dst[0] = LIFT(src[0], ((mul*2*ref[0]+add)>>shift), inverse);
        dst += dst_step;
        src += src_step;
    }

    for(i=0; i<w; i++){
        dst[i*dst_step] =
            LIFT(src[i*src_step],
                 ((mul*(ref[i*ref_step] + ref[(i+1)*ref_step])+add)>>shift),
                 inverse);
    }

    if(mirror_right){
        dst[w*dst_step] =
            LIFT(src[w*src_step],
                 ((mul*2*ref[w*ref_step]+add)>>shift),
                 inverse);
    }
}

static av_always_inline void
inv_lift(IDWTELEM *dst, IDWTELEM *src, IDWTELEM *ref,
         int dst_step, int src_step, int ref_step,
         int width, int mul, int add, int shift,
         int highpass, int inverse){
    const int mirror_left= !highpass;
    const int mirror_right= (width&1) ^ highpass;
    const int w= (width>>1) - 1 + (highpass & width);
    int i;

#define LIFT(src, ref, inv) ((src) + ((inv) ? - (ref) : + (ref)))
    if(mirror_left){
        dst[0] = LIFT(src[0], ((mul*2*ref[0]+add)>>shift), inverse);
        dst += dst_step;
        src += src_step;
    }

    for(i=0; i<w; i++){
        dst[i*dst_step] =
            LIFT(src[i*src_step],
                 ((mul*(ref[i*ref_step] + ref[(i+1)*ref_step])+add)>>shift),
                 inverse);
    }

    if(mirror_right){
        dst[w*dst_step] =
            LIFT(src[w*src_step],
                 ((mul*2*ref[w*ref_step]+add)>>shift),
                 inverse);
    }
}

#ifndef liftS
static av_always_inline void
liftS(DWTELEM *dst, DWTELEM *src, DWTELEM *ref,
      int dst_step, int src_step, int ref_step,
      int width, int mul, int add, int shift,
      int highpass, int inverse){
    const int mirror_left= !highpass;
    const int mirror_right= (width&1) ^ highpass;
    const int w= (width>>1) - 1 + (highpass & width);
    int i;

    assert(shift == 4);
#define LIFTS(src, ref, inv) \
        ((inv) ? \
            (src) + (((ref) + 4*(src))>>shift): \
            -((-16*(src) + (ref) + add/4 + 1 + (5<<25))/(5*4) - (1<<23)))
    if(mirror_left){
        dst[0] = LIFTS(src[0], mul*2*ref[0]+add, inverse);
        dst += dst_step;
        src += src_step;
    }

    for(i=0; i<w; i++){
        dst[i*dst_step] =
            LIFTS(src[i*src_step],
                  mul*(ref[i*ref_step] + ref[(i+1)*ref_step])+add,
                  inverse);
    }

    if(mirror_right){
        dst[w*dst_step] =
            LIFTS(src[w*src_step], mul*2*ref[w*ref_step]+add, inverse);
    }
}
static av_always_inline void
inv_liftS(IDWTELEM *dst, IDWTELEM *src, IDWTELEM *ref,
          int dst_step, int src_step, int ref_step,
          int width, int mul, int add, int shift,
          int highpass, int inverse){
    const int mirror_left= !highpass;
    const int mirror_right= (width&1) ^ highpass;
    const int w= (width>>1) - 1 + (highpass & width);
    int i;

    assert(shift == 4);
#define LIFTS(src, ref, inv) \
    ((inv) ? \
        (src) + (((ref) + 4*(src))>>shift): \
        -((-16*(src) + (ref) + add/4 + 1 + (5<<25))/(5*4) - (1<<23)))
    if(mirror_left){
        dst[0] = LIFTS(src[0], mul*2*ref[0]+add, inverse);
        dst += dst_step;
        src += src_step;
    }

    for(i=0; i<w; i++){
        dst[i*dst_step] =
            LIFTS(src[i*src_step],
                  mul*(ref[i*ref_step] + ref[(i+1)*ref_step])+add,
                  inverse);
    }

    if(mirror_right){
        dst[w*dst_step] =
            LIFTS(src[w*src_step], mul*2*ref[w*ref_step]+add, inverse);
    }
}
#endif

static void horizontal_decompose53i(DWTELEM *b, int width){
    DWTELEM temp[width];
    const int width2= width>>1;
    int x;
    const int w2= (width+1)>>1;

    for(x=0; x<width2; x++){
        temp[x   ]= b[2*x    ];
        temp[x+w2]= b[2*x + 1];
    }
    if(width&1)
        temp[x   ]= b[2*x    ];
#if 0
    {
    int A1,A2,A3,A4;
    A2= temp[1       ];
    A4= temp[0       ];
    A1= temp[0+width2];
    A1 -= (A2 + A4)>>1;
    A4 += (A1 + 1)>>1;
    b[0+width2] = A1;
    b[0       ] = A4;
    for(x=1; x+1<width2; x+=2){
        A3= temp[x+width2];
        A4= temp[x+1     ];
        A3 -= (A2 + A4)>>1;
        A2 += (A1 + A3 + 2)>>2;
        b[x+width2] = A3;
        b[x       ] = A2;

        A1= temp[x+1+width2];
        A2= temp[x+2       ];
        A1 -= (A2 + A4)>>1;
        A4 += (A1 + A3 + 2)>>2;
        b[x+1+width2] = A1;
        b[x+1       ] = A4;
    }
    A3= temp[width-1];
    A3 -= A2;
    A2 += (A1 + A3 + 2)>>2;
    b[width -1] = A3;
    b[width2-1] = A2;
    }
#else
    lift(b+w2, temp+w2, temp, 1, 1, 1, width, -1, 0, 1, 1, 0);
    lift(b   , temp   , b+w2, 1, 1, 1, width,  1, 2, 2, 0, 0);
#endif
}

static void vertical_decompose53iH0(DWTELEM *b0, DWTELEM *b1, DWTELEM *b2, int width){
    int i;

    for(i=0; i<width; i++){
        b1[i] -= (b0[i] + b2[i])>>1;
    }
}

static void vertical_decompose53iL0(DWTELEM *b0, DWTELEM *b1, DWTELEM *b2, int width){
    int i;

    for(i=0; i<width; i++){
        b1[i] += (b0[i] + b2[i] + 2)>>2;
    }
}

static void spatial_decompose53i(DWTELEM *buffer, int width, int height, int stride){
    int y;
    DWTELEM *b0= buffer + mirror(-2-1, height-1)*stride;
    DWTELEM *b1= buffer + mirror(-2  , height-1)*stride;

    for(y=-2; y<height; y+=2){
        DWTELEM *b2= buffer + mirror(y+1, height-1)*stride;
        DWTELEM *b3= buffer + mirror(y+2, height-1)*stride;

{START_TIMER
        if(y+1<(unsigned)height) horizontal_decompose53i(b2, width);
        if(y+2<(unsigned)height) horizontal_decompose53i(b3, width);
STOP_TIMER("horizontal_decompose53i")}

{START_TIMER
        if(y+1<(unsigned)height) vertical_decompose53iH0(b1, b2, b3, width);
        if(y+0<(unsigned)height) vertical_decompose53iL0(b0, b1, b2, width);
STOP_TIMER("vertical_decompose53i*")}

        b0=b2;
        b1=b3;
    }
}

static void horizontal_decompose97i(DWTELEM *b, int width){
    DWTELEM temp[width];
    const int w2= (width+1)>>1;

    lift (temp+w2, b    +1, b      , 1, 2, 2, width,  W_AM, W_AO, W_AS, 1, 1);
    liftS(temp   , b      , temp+w2, 1, 2, 1, width,  W_BM, W_BO, W_BS, 0, 0);
    lift (b   +w2, temp+w2, temp   , 1, 1, 1, width,  W_CM, W_CO, W_CS, 1, 0);
    lift (b      , temp   , b   +w2, 1, 1, 1, width,  W_DM, W_DO, W_DS, 0, 0);
}


static void vertical_decompose97iH0(DWTELEM *b0, DWTELEM *b1, DWTELEM *b2, int width){
    int i;

    for(i=0; i<width; i++){
        b1[i] -= (W_AM*(b0[i] + b2[i])+W_AO)>>W_AS;
    }
}

static void vertical_decompose97iH1(DWTELEM *b0, DWTELEM *b1, DWTELEM *b2, int width){
    int i;

    for(i=0; i<width; i++){
        b1[i] += (W_CM*(b0[i] + b2[i])+W_CO)>>W_CS;
    }
}

static void vertical_decompose97iL0(DWTELEM *b0, DWTELEM *b1, DWTELEM *b2, int width){
    int i;

    for(i=0; i<width; i++){
#ifdef liftS
        b1[i] -= (W_BM*(b0[i] + b2[i])+W_BO)>>W_BS;
#else
        b1[i] = (16*4*b1[i] - 4*(b0[i] + b2[i]) + W_BO*5 + (5<<27)) / (5*16) - (1<<23);
#endif
    }
}

static void vertical_decompose97iL1(DWTELEM *b0, DWTELEM *b1, DWTELEM *b2, int width){
    int i;

    for(i=0; i<width; i++){
        b1[i] += (W_DM*(b0[i] + b2[i])+W_DO)>>W_DS;
    }
}

static void spatial_decompose97i(DWTELEM *buffer, int width, int height, int stride){
    int y;
    DWTELEM *b0= buffer + mirror(-4-1, height-1)*stride;
    DWTELEM *b1= buffer + mirror(-4  , height-1)*stride;
    DWTELEM *b2= buffer + mirror(-4+1, height-1)*stride;
    DWTELEM *b3= buffer + mirror(-4+2, height-1)*stride;

    for(y=-4; y<height; y+=2){
        DWTELEM *b4= buffer + mirror(y+3, height-1)*stride;
        DWTELEM *b5= buffer + mirror(y+4, height-1)*stride;

{START_TIMER