通用Fibonacci LFSR的反向输出

Question

假设我们有一些Fibonacci LFSR，它输出一些序列。

如何改变启动LFSR，使其输出完全相同的序列，但以相反的顺序？

Answer 1

在这里提供lfsr和反向lfsr的代码。第一个是来自wikipedia的lfsr代码，第二个是反向lfsr。

#include <stdio.h>

int main(void)
{
    unsigned short start_state = 0xace1;
    unsigned lfsr = start_state;
    unsigned int period = 0;

    do
    {
        unsigned short lsb = lfsr & 1;
        lfsr >>= 1;
        lfsr ^= (-lsb) & 0xb400;
        ++period;

        printf("%x\n", lfsr);
    } while (lfsr != start_state);

    return 0;
}

#include <stdio.h>

unsigned short bit_revert(unsigned short v)
{
    int i = 0;
    unsigned short lsb = 0;
    unsigned short n = 0;

    for (i = 0; i < sizeof(unsigned short) * 8; i++)
    {
        lsb = v & 1;
        v >>= 1;
        n <<= 1;
        n |= lsb;
    }

    return n;
}

int main(void)
{
    unsigned short start_state = 0xace1;
    unsigned lfsr = start_state;
    unsigned int period = 0;

    do
    {
        unsigned short lsb = lfsr & 1;
        lfsr >>= 1;
        lfsr ^= (-lsb) & 0x8016;
        ++period;

        printf("%x\n", bit_revert(lfsr));
    } while (lfsr != start_state);

    return 0;
}