[code 小心得]C 語言 位元操作

Hi  大家好

今天要談的是... C  位元操作  請見下列PDF檔案介紹，現在想想  我到現在  還是 不懂C 啊．

http://140.129.118.16/~richwang/99-2-Courses/About_C_BitOperation.pdf

廢話 不多說  請見書本 舉例囉


#include void main(void) { unsigned int original = 0xABC; unsigned int result = 0; unsigned int mask = 0xF; //最右邊四bit printf("original =%X\n", original); result |= original&mask; //將original 右邊四bit放到result //取得第二個位數 original >>= 4; //將original右移四個位置 result <<= 4; //讓出空間給下一位數 result |= original&mask; //將original右邊四個位元放到result //取得第三個位數 original >>= 4; result <<= 4; result |= original&mask; printf("result = %X\n", result); }
執行結果： original = ABC

                     result = CBA

基本上就是到回去

另外 較常見到會做 位元操作  好像是在 驅動程式 或是  畫圖影像處理 那一類

例如下列 一個對 FrameBuffer 做操作的範例

#include #include #include #include #include #include #include int main() { int fbfd = 0; struct fb_var_screeninfo vinfo; struct fb_fix_screeninfo finfo; long int screensize = 0; char *fbp = 0; int x = 0, y = 0; long int location = 0; // Open the file for reading and writing fbfd = open("/dev/fb0", O_RDWR); if (fbfd == -1) { perror("Error: cannot open framebuffer device"); exit(1); } printf("The framebuffer device was opened successfully.\n"); // Get fixed screen information if (ioctl(fbfd, FBIOGET_FSCREENINFO, &finfo) == -1) { perror("Error reading fixed information"); exit(2); } // Get variable screen information if (ioctl(fbfd, FBIOGET_VSCREENINFO, &vinfo) == -1) { perror("Error reading variable information"); exit(3); } printf("%dx%d, %dbpp\n", vinfo.xres, vinfo.yres, vinfo.bits_per_pixel); // Figure out the size of the screen in bytes screensize = vinfo.xres * vinfo.yres * vinfo.bits_per_pixel / 8; // Map the device to memory fbp = (char *)mmap(0, screensize, PROT_READ | PROT_WRITE, MAP_SHARED, fbfd, 0); if ((int)fbp == -1) { perror("Error: failed to map framebuffer device to memory"); exit(4); } printf("The framebuffer device was mapped to memory successfully.\n"); x = 300; y = 100; // Where we are going to put the pixel // Figure out where in memory to put the pixel for (y = 100; y < 300; y++) for (x = 100; x < 300; x++) { location = (x+vinfo.xoffset) * (vinfo.bits_per_pixel/8) + (y+vinfo.yoffset) * finfo.line_length; if (vinfo.bits_per_pixel == 32) { *(fbp + location) = 100; // Some blue *(fbp + location + 1) = 15+(x-100)/2; // A little green *(fbp + location + 2) = 200-(y-100)/5; // A lot of red *(fbp + location + 3) = 0; // No transparency } else { //assume 16bpp int b = 10; int g = (x-100)/6; // A little green int r = 31-(y-100)/16; // A lot of red unsigned short int t = r<<11 | g << 5 | b; *((unsigned short int*)(fbp + location)) = t; } } munmap(fbp, screensize); close(fbfd); return 0; }
上列來源網址 http://www.cubieforums.com/index.php?topic=33.0 以上感謝 下台一鞠躬