superblock_row_inc = 3 * s->fragment_width;
superblock_row_inc = 3 * s->fragment_width - (s->y_superblock_width * 4 - s->fragment_width);
static void init_block_mapping(Vp3DecodeContext *s) {    int i, j;    signed int hilbert_walk_y[16];    signed int hilbert_walk_c[16];    signed int hilbert_walk_mb[4];    int current_fragment = 0;    int current_width = 0;    int current_height = 0;    int right_edge = 0;    int bottom_edge = 0;    int superblock_row_inc = 0;    int *hilbert = NULL;    int mapping_index = 0;    int current_macroblock;    int c_fragment;    signed char travel_width[16] = {         1,  1,  0, -1,          0,  0,  1,  0,         1,  0,  1,  0,         0, -1,  0,  1    };    signed char travel_height[16] = {         0,  0,  1,  0,         1,  1,  0, -1,         0,  1,  0, -1,        -1,  0, -1,  0    };    signed char travel_width_mb[4] = {         1,  0,  1,  0    };    signed char travel_height_mb[4] = {         0,  1,  0, -1    };    debug_vp3("  vp3: initialize block mapping tables\n");    /* figure out hilbert pattern per these frame dimensions */    hilbert_walk_y[0]  = 1;    hilbert_walk_y[1]  = 1;    hilbert_walk_y[2]  = s->fragment_width;    hilbert_walk_y[3]  = -1;    hilbert_walk_y[4]  = s->fragment_width;    hilbert_walk_y[5]  = s->fragment_width;    hilbert_walk_y[6]  = 1;    hilbert_walk_y[7]  = -s->fragment_width;    hilbert_walk_y[8]  = 1;    hilbert_walk_y[9]  = s->fragment_width;    hilbert_walk_y[10]  = 1;    hilbert_walk_y[11] = -s->fragment_width;    hilbert_walk_y[12] = -s->fragment_width;    hilbert_walk_y[13] = -1;    hilbert_walk_y[14] = -s->fragment_width;    hilbert_walk_y[15] = 1;    hilbert_walk_c[0]  = 1;    hilbert_walk_c[1]  = 1;    hilbert_walk_c[2]  = s->fragment_width / 2;    hilbert_walk_c[3]  = -1;    hilbert_walk_c[4]  = s->fragment_width / 2;    hilbert_walk_c[5]  = s->fragment_width / 2;    hilbert_walk_c[6]  = 1;    hilbert_walk_c[7]  = -s->fragment_width / 2;    hilbert_walk_c[8]  = 1;    hilbert_walk_c[9]  = s->fragment_width / 2;    hilbert_walk_c[10]  = 1;    hilbert_walk_c[11] = -s->fragment_width / 2;    hilbert_walk_c[12] = -s->fragment_width / 2;    hilbert_walk_c[13] = -1;    hilbert_walk_c[14] = -s->fragment_width / 2;    hilbert_walk_c[15] = 1;    hilbert_walk_mb[0] = 1;    hilbert_walk_mb[1] = s->macroblock_width;    hilbert_walk_mb[2] = 1;    hilbert_walk_mb[3] = -s->macroblock_width;    /* iterate through each superblock (all planes) and map the fragments */    for (i = 0; i < s->superblock_count; i++) {        debug_init("    superblock %d (u starts @ %d, v starts @ %d)\n",            i, s->u_superblock_start, s->v_superblock_start);        /* time to re-assign the limits? */        if (i == 0) {            /* start of Y superblocks */            right_edge = s->fragment_width;            bottom_edge = s->fragment_height;            current_width = 0;            current_height = 0;            superblock_row_inc = 3 * s->fragment_width;            hilbert = hilbert_walk_y;            /* the first operation for this variable is to advance by 1 */            current_fragment = -1;        } else if (i == s->u_superblock_start) {            /* start of U superblocks */            right_edge = s->fragment_width / 2;            bottom_edge = s->fragment_height / 2;            current_width = 0;            current_height = 0;            superblock_row_inc = 3 * (s->fragment_width / 2);            hilbert = hilbert_walk_c;            /* the first operation for this variable is to advance by 1 */            current_fragment = s->u_fragment_start - 1;        } else if (i == s->v_superblock_start) {            /* start of V superblocks */            right_edge = s->fragment_width / 2;            bottom_edge = s->fragment_height / 2;            current_width = 0;            current_height = 0;            superblock_row_inc = 3 * (s->fragment_width / 2);            hilbert = hilbert_walk_c;            /* the first operation for this variable is to advance by 1 */            current_fragment = s->v_fragment_start - 1;        }        if (current_width >= right_edge) {            /* reset width and move to next superblock row */            current_width = 0;            current_height += 4;            /* fragment is now at the start of a new superblock row */            current_fragment += superblock_row_inc;        }        /* iterate through all 16 fragments in a superblock */        for (j = 0; j < 16; j++) {            current_fragment += hilbert[j];            current_height += travel_height[j];            /* check if the fragment is in bounds */            if ((current_width <= right_edge) &&                (current_height < bottom_edge)) {                s->superblock_fragments[mapping_index] = current_fragment;                debug_init("    mapping fragment %d to superblock %d, position %d\n",                     s->superblock_fragments[mapping_index], i, j);            } else {                s->superblock_fragments[mapping_index] = -1;                debug_init("    superblock %d, position %d has no fragment\n",                     i, j);            }            current_width += travel_width[j];            mapping_index++;        }    }    /* initialize the superblock <-> macroblock mapping; iterate through     * all of the Y plane superblocks to build this mapping */    right_edge = s->macroblock_width;    bottom_edge = s->macroblock_height;    current_width = 0;    current_height = 0;    superblock_row_inc = s->macroblock_width;    hilbert = hilbert_walk_mb;    mapping_index = 0;    current_macroblock = -1;    for (i = 0; i < s->u_superblock_start; i++) {        if (current_width >= right_edge) {            /* reset width and move to next superblock row */            current_width = 0;            current_height += 2;            /* macroblock is now at the start of a new superblock row */            current_macroblock += superblock_row_inc;        }        /* iterate through each potential macroblock in the superblock */        for (j = 0; j < 4; j++) {            current_macroblock += hilbert_walk_mb[j];            current_height += travel_height_mb[j];            /* check if the macroblock is in bounds */            if ((current_width <= right_edge) &&                (current_height < bottom_edge)) {                s->superblock_macroblocks[mapping_index] = current_macroblock;                debug_init("    mapping macroblock %d to superblock %d, position %d\n",                    s->superblock_macroblocks[mapping_index], i, j);            } else {                s->superblock_macroblocks[mapping_index] = -1;                debug_init("    superblock %d, position %d has no macroblock\n",                    i, j);            }            current_width += travel_width_mb[j];            mapping_index++;        }    }    /* initialize the macroblock <-> fragment mapping */    current_fragment = 0;    current_macroblock = 0;    mapping_index = 0;    for (i = 0; i < s->fragment_height; i += 2) {        for (j = 0; j < s->fragment_width; j += 2) {            debug_init("    macroblock %d contains fragments: ", current_macroblock);            s->all_fragments[current_fragment].macroblock = current_macroblock;            s->macroblock_fragments[mapping_index++] = current_fragment;            debug_init("%d ", current_fragment);            if (j + 1 < s->fragment_width) {                s->all_fragments[current_fragment + 1].macroblock = current_macroblock;                s->macroblock_fragments[mapping_index++] = current_fragment + 1;                debug_init("%d ", current_fragment + 1);            } else                s->macroblock_fragments[mapping_index++] = -1;            if (i + 1 < s->fragment_height) {                s->all_fragments[current_fragment + s->fragment_width].macroblock =                     current_macroblock;                s->macroblock_fragments[mapping_index++] =                     current_fragment + s->fragment_width;                debug_init("%d ", current_fragment + s->fragment_width);            } else                s->macroblock_fragments[mapping_index++] = -1;            if ((j + 1 < s->fragment_width) && (i + 1 < s->fragment_height)) {                s->all_fragments[current_fragment + s->fragment_width + 1].macroblock =                     current_macroblock;                s->macroblock_fragments[mapping_index++] =                     current_fragment + s->fragment_width + 1;                debug_init("%d ", current_fragment + s->fragment_width + 1);            } else                s->macroblock_fragments[mapping_index++] = -1;            /* C planes */            c_fragment = s->u_fragment_start +                 (i * s->fragment_width / 4) + (j / 2);        s->all_fragments[c_fragment].macroblock = s->macroblock_count;            s->macroblock_fragments[mapping_index++] = c_fragment;            debug_init("%d ", c_fragment);            c_fragment = s->v_fragment_start +                 (i * s->fragment_width / 4) + (j / 2);        s->all_fragments[c_fragment].macroblock = s->macroblock_count;            s->macroblock_fragments[mapping_index++] = c_fragment;            debug_init("%d ", c_fragment);            debug_init("\n");            if (j + 2 <= s->fragment_width)                current_fragment += 2;            else                 current_fragment++;            current_macroblock++;        }        current_fragment += s->fragment_width;    }}