按位向右旋转

Question

我试图将这个C函数转换为Python;

typedef unsigned long var;
    /* Bit rotate rightwards */
    var ror(var v,unsigned int bits) {
        return (v>>bits)|(v<<(8*sizeof(var)-bits));
    }

我已经尝试过谷歌搜索一些解决方案,但我似乎无法让他们中的任何一个给出与此处相同的结果.

这是我从另一个程序中找到的一个解决方案;

def mask1(n):
   """Return a bitmask of length n (suitable for masking against an
      int to coerce the size to a given length)
   """
   if n >= 0:
       return 2**n - 1
   else:
       return 0

def ror(n, rotations=1, width=8):
    """Return a given number of bitwise right rotations of an integer n,
       for a given bit field width.
    """
    rotations %= width
    if rotations < 1:
        return n
    n &= mask1(width)
    return (n >> rotations) | ((n << (8 * width - rotations)))

我正试图btishift key = 0xf0f0f0f0f123456.C代码000000000f0f0f12在调用时给出; ror(key, 8 << 1)和Python给出; 0x0f0f0f0f0f123456(原始输入!)

Answer 1

您的C输出与您提供的功能不匹配.这可能是因为您没有正确打印它.这个程序:

#include <stdio.h>
#include <stdint.h>

uint64_t ror(uint64_t v, unsigned int bits) 
{
    return (v>>bits) | (v<<(8*sizeof(uint64_t)-bits));
}

int main(void)
{
    printf("%llx\n", ror(0x0123456789abcdef, 4));
    printf("%llx\n", ror(0x0123456789abcdef, 8));
    printf("%llx\n", ror(0x0123456789abcdef, 12));
    printf("%llx\n", ror(0x0123456789abcdef, 16));
    return 0;
}

产生以下输出:

f0123456789abcde
ef0123456789abcd
def0123456789abc
cdef0123456789ab

要在Python中生成ror函数,请参阅这篇优秀文章:http://www.falatic.com/index.php/108/python-and-bitwise-rotation

这个Python 2代码产生与上面的C程序相同的输出:

ror = lambda val, r_bits, max_bits: \
    ((val & (2**max_bits-1)) >> r_bits%max_bits) | \
    (val << (max_bits-(r_bits%max_bits)) & (2**max_bits-1))

print "%x" % ror(0x0123456789abcdef, 4, 64)
print "%x" % ror(0x0123456789abcdef, 8, 64)
print "%x" % ror(0x0123456789abcdef, 12, 64)
print "%x" % ror(0x0123456789abcdef, 16, 64)

Answer 2

我在Python中找到的最短方法：（注意这仅适用于整数作为输入）

def ror(n,rotations,width):
    return (2**width-1)&(n>>rotations|n<<(width-rotations))