c++ - 位扩展字节数组

Question

我有一种情况需要将动态大小的字节数组放大 3。

例子:

10101010 11001100

到

11100011 10001110 00111000 11111100 00001111 11000000

我已经使用这里的算法生成了一个查找表。

https://stackoverflow.com/a/9044057/280980

static const uint32_t bitExpandTable[256] = {
00000000, 0x000007, 0x000038, 0x00003f, 0x0001c0, 0x0001c7, 0x0001f8, 0x0001ff,
0x000e00, 0x000e07, 0x000e38, 0x000e3f, 0x000fc0, 0x000fc7, 0x000ff8, 0x000fff,
0x007000, 0x007007, 0x007038, 0x00703f, 0x0071c0, 0x0071c7, 0x0071f8, 0x0071ff,
0x007e00, 0x007e07, 0x007e38, 0x007e3f, 0x007fc0, 0x007fc7, 0x007ff8, 0x007fff,
0x038000, 0x038007, 0x038038, 0x03803f, 0x0381c0, 0x0381c7, 0x0381f8, 0x0381ff,
0x038e00, 0x038e07, 0x038e38, 0x038e3f, 0x038fc0, 0x038fc7, 0x038ff8, 0x038fff,
0x03f000, 0x03f007, 0x03f038, 0x03f03f, 0x03f1c0, 0x03f1c7, 0x03f1f8, 0x03f1ff,
0x03fe00, 0x03fe07, 0x03fe38, 0x03fe3f, 0x03ffc0, 0x03ffc7, 0x03fff8, 0x03ffff,
0x1c0000, 0x1c0007, 0x1c0038, 0x1c003f, 0x1c01c0, 0x1c01c7, 0x1c01f8, 0x1c01ff,
0x1c0e00, 0x1c0e07, 0x1c0e38, 0x1c0e3f, 0x1c0fc0, 0x1c0fc7, 0x1c0ff8, 0x1c0fff,
0x1c7000, 0x1c7007, 0x1c7038, 0x1c703f, 0x1c71c0, 0x1c71c7, 0x1c71f8, 0x1c71ff,
0x1c7e00, 0x1c7e07, 0x1c7e38, 0x1c7e3f, 0x1c7fc0, 0x1c7fc7, 0x1c7ff8, 0x1c7fff,
0x1f8000, 0x1f8007, 0x1f8038, 0x1f803f, 0x1f81c0, 0x1f81c7, 0x1f81f8, 0x1f81ff,
0x1f8e00, 0x1f8e07, 0x1f8e38, 0x1f8e3f, 0x1f8fc0, 0x1f8fc7, 0x1f8ff8, 0x1f8fff,
0x1ff000, 0x1ff007, 0x1ff038, 0x1ff03f, 0x1ff1c0, 0x1ff1c7, 0x1ff1f8, 0x1ff1ff,
0x1ffe00, 0x1ffe07, 0x1ffe38, 0x1ffe3f, 0x1fffc0, 0x1fffc7, 0x1ffff8, 0x1fffff,
0xe00000, 0xe00007, 0xe00038, 0xe0003f, 0xe001c0, 0xe001c7, 0xe001f8, 0xe001ff,
0xe00e00, 0xe00e07, 0xe00e38, 0xe00e3f, 0xe00fc0, 0xe00fc7, 0xe00ff8, 0xe00fff,
0xe07000, 0xe07007, 0xe07038, 0xe0703f, 0xe071c0, 0xe071c7, 0xe071f8, 0xe071ff,
0xe07e00, 0xe07e07, 0xe07e38, 0xe07e3f, 0xe07fc0, 0xe07fc7, 0xe07ff8, 0xe07fff,
0xe38000, 0xe38007, 0xe38038, 0xe3803f, 0xe381c0, 0xe381c7, 0xe381f8, 0xe381ff,
0xe38e00, 0xe38e07, 0xe38e38, 0xe38e3f, 0xe38fc0, 0xe38fc7, 0xe38ff8, 0xe38fff,
0xe3f000, 0xe3f007, 0xe3f038, 0xe3f03f, 0xe3f1c0, 0xe3f1c7, 0xe3f1f8, 0xe3f1ff,
0xe3fe00, 0xe3fe07, 0xe3fe38, 0xe3fe3f, 0xe3ffc0, 0xe3ffc7, 0xe3fff8, 0xe3ffff,
0xfc0000, 0xfc0007, 0xfc0038, 0xfc003f, 0xfc01c0, 0xfc01c7, 0xfc01f8, 0xfc01ff,
0xfc0e00, 0xfc0e07, 0xfc0e38, 0xfc0e3f, 0xfc0fc0, 0xfc0fc7, 0xfc0ff8, 0xfc0fff,
0xfc7000, 0xfc7007, 0xfc7038, 0xfc703f, 0xfc71c0, 0xfc71c7, 0xfc71f8, 0xfc71ff,
0xfc7e00, 0xfc7e07, 0xfc7e38, 0xfc7e3f, 0xfc7fc0, 0xfc7fc7, 0xfc7ff8, 0xfc7fff,
0xff8000, 0xff8007, 0xff8038, 0xff803f, 0xff81c0, 0xff81c7, 0xff81f8, 0xff81ff,
0xff8e00, 0xff8e07, 0xff8e38, 0xff8e3f, 0xff8fc0, 0xff8fc7, 0xff8ff8, 0xff8fff,
0xfff000, 0xfff007, 0xfff038, 0xfff03f, 0xfff1c0, 0xfff1c7, 0xfff1f8, 0xfff1ff,
0xfffe00, 0xfffe07, 0xfffe38, 0xfffe3f, 0xffffc0, 0xffffc7, 0xfffff8, 0xffffff,
};

我已经尝试使用 LUT 遍历字节数组，将前 3 个字节 memcpy 到新数组。然而，我的输出看起来从来都不正确。

有没有人对如何有效地实现它有任何建议？这将在嵌入式 ARM 处理器上运行。

编辑

LUT测试

uint8_t msg[] = { 0xaa, 0x02, 0x43, 0x5a, 0x8d, 0x06, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xd0, 0x84, 0xc6, 0x2d, 0x00, 0xb9 };

uint8_t expanded_msg[63] = { 0 };
uint8_t tmp_val = 0;
uint32_t lut_val;
for (int i = 0; i < 21; i++)
{
    tmp_val = *(uint8_t*)(&msg + i);
    lut_val = bitExpandTable[tmp_val];
    memcpy(&expanded_msg[(i * 3)], &lut_val, 3);
}

print_binary(&msg, 21);
print_binary(&expanded_msg, sizeof(expanded_msg));

输出

[ 10101010 00000010 01000011 01011010 10001101 00000110 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 11010000 10000100 11000110 00101101 00000000 10111001 ]

[ 00111000 10001110 11100011 00000000 00000000 00000000 11000111 10001111 00000011 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000111 01110000 00011100 00000111 11110000 00000011 11111111 11111111 00011111 11000111 11110001 11100011 00000000 00000000 00000000 11111111 11111111 11111111 11000000 10000001 11100011 00000000 00000000 00000000 00000111 01110000 00011100 00111000 10000000 00011111 11111111 11111111 00011111 11000111 11110001 11100011 00000000 00000000 00000000 11111111 11111111 11111111 ]

Answer 1

您的表(或您复制数据的方式)存在字节顺序问题:

对于第一个输入字节

10101010

你的输出是

a        b        c
00111000 10001110 11100011

但应该是

c        b        a
11100011 10001110 00111000

所以第一个和第三个字节需要交换(依此类推)

我不会更改表以适应 memcpy，而是做类似的事情

int j = 0;
for (int i = 0; i < 21; i++) {
  lut_val = bitExpandTable[msg[i]];
  expanded_msg[j++] = (uint8_t) (lut_val >> 16);
  expanded_msg[j++] = (uint8_t) (lut_val >> 8);
  expanded_msg[j++] = (uint8_t) lut_val;
}