字段打包形成一个字节

Question

我正在努力学习如何将四个单独的值打包到一个字节中。我试图获得 0x91 的十六进制输出，二进制表示应该是 10010001 但我得到的输出分别是：0x1010001 和 16842753。或者有更好的方法吗？

uint8_t globalColorTableFlag = 1;

uint8_t colorResolution = 001;

uint8_t sortFlag = 0;

uint8_t sizeOfGlobalColorTable = 001;

uint32_t packed = ((globalColorTableFlag << 24) | (colorResolution << 16) | (sortFlag << 8) | (sizeOfGlobalColorTable << 0));

NSLog(@"%d",packed); // Logs 16842753, should be: 10010001
NSLog(@"0x%02X",packed); // Logs 0x1010001, should be: 0x91

Answer 1

尝试以下操作：

/* packed starts at 0 */
uint8_t packed = 0;

/* one bit of the flag is kept and shifted to the last position */
packed |= ((globalColorTableFlag & 0x1) << 7);
/* three bits of the resolution are kept and shifted to the fifth position */
packed |= ((colorResolution & 0x7) << 4);
/* one bit of the flag is kept and shifted to the fourth position */
packed |= ((sortFlag & 0x1) << 3);
/* three bits are kept and left in the first position */
packed |= ((sizeOfGlobalColorTable & 0x7) << 0);

有关十六进制和二进制数字之间关系的解释，请参阅此答案：

按位运算见：

Answer 2

packed = ((globalColorTableFlag & 1) << 7) +
    ((colorResolution & 0x7) << 4) +
    ((sortFlag & 1) << 3) +
    ((sizeOfGlobalColorTable & 0x7);

字段打包形成一个字节

Field packing to form a single byte

c

hex

objective-c

bitwise-operators