C reverse bits in unsigned integer

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Reversing the bits in a word is annoying and it’s easier just to output them in reverse order. E.g.,

void write_u32(uint32_t x)
{
    int i;
    for (i = 0; i < 32; ++i)
        putchar((x & ((uint32_t) 1 << (31 - i)) ? '1' : '0');
}

Here’s the typical solution to reversing the bit order:

uint32_t reverse(uint32_t x)
{
    x = ((x >> 1) & 0x55555555u) | ((x & 0x55555555u) << 1);
    x = ((x >> 2) & 0x33333333u) | ((x & 0x33333333u) << 2);
    x = ((x >> 4) & 0x0f0f0f0fu) | ((x & 0x0f0f0f0fu) << 4);
    x = ((x >> 8) & 0x00ff00ffu) | ((x & 0x00ff00ffu) << 8);
    x = ((x >> 16) & 0xffffu) | ((x & 0xffffu) << 16);
    return x;
}

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