for (l = 1; l <= sxy; l++) { i = x_curr + xoff - l; j = y_curr + yoff - l; for (k = 0; k < 8*l; k++) { if (i>=ilow && i<=ihigh && j>=jlow && j<=jhigh) { ii = search_area + (i-ilow) + (j-jlow)*h_length; sad = SAD_Macroblock(ii, act_block, h_length, Min_FRAME[0]); if (sad < Min_FRAME[0]) { MV_FRAME[0].x = i - x_curr; MV_FRAME[0].y = j - y_curr; Min_FRAME[0] = sad; } } if(k<2*l) i++; else if (k<4*l) j++; else if (k<6*l) i--; else j--; } }将这段代码改为对数搜索算法

将Diamond Search算法改为对数搜索算法的代码实现如下：

// 定义搜索区域的大小
int search_size = 16;

// 计算搜索区域的起始点和结束点
int search_x_start = x_curr + xoff - search_size / 2;
int search_x_end = search_x_start + search_size - 1;
int search_y_start = y_curr + yoff - search_size / 2;
int search_y_end = search_y_start + search_size - 1;

// 定义搜索精度，n为划分子区域的次数
int n = 3;
int search_step = search_size / pow(2, n);

// 定义当前最小SAD和对应的MV
int min_sad = INT_MAX;
MV best_mv;

// 对搜索区域进行分块，每个子区域的大小为search_step * search_step
for (int i = search_x_start; i <= search_x_end; i += search_step) {
    for (int j = search_y_start; j <= search_y_end; j += search_step) {
        // 计算子区域的起始点和结束点
        int sub_search_x_start = i;
        int sub_search_x_end = i + search_step - 1;
        int sub_search_y_start = j;
        int sub_search_y_end = j + search_step - 1;

        // 限制子区域在搜索区域内
        sub_search_x_start = max(sub_search_x_start, ilow);
        sub_search_x_end = min(sub_search_x_end, ihigh);
        sub_search_y_start = max(sub_search_y_start, jlow);
        sub_search_y_end = min(sub_search_y_end, jhigh);

        // 对子区域内的点进行搜索
        for (int x = sub_search_x_start; x <= sub_search_x_end; x++) {
            for (int y = sub_search_y_start; y <= sub_search_y_end; y++) {
                int ii = search_area + (x - ilow) + (y - jlow) * h_length;
                int sad = SAD_Macroblock(ii, act_block, h_length, Min_FRAME[0]);
                if (sad < min_sad) {
                    best_mv.x = x - x_curr;
                    best_mv.y = y - y_curr;
                    min_sad = sad;
                }
            }
        }
    }
}

对数搜索算法的核心思想是将搜索区域分成若干个小块，每个小块的大小为2的n次方，n为正整数。然后在每个小块内进行搜索，选择最小的SAD值对应的MV作为最终结果。通过不断缩小搜索区域的大小，可以达到较高的搜索精度和较快的搜索速度。