我正在尝试将此 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));
}
我已经尝试使用谷歌搜索一些解决方案,但我似乎无法获得与此处相同的结果。
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)))
我正在尝试 btishift key = 0xf0f0f0f0f123456
。 C 代码在调用时给出 000000000f0f0f12
; ror(key, 8 << 1)
和 Python 给出; 0x0f0f0f0f0f123456
(原始输入!)
最佳答案
您的 C 输出与您提供的函数不匹配。这大概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
To produce an ror function in Python I refer you to this excellent article: http://www.falatic.com/index.php/108/python-and-bitwise-rotation
This Python 2 code produces the same output as the C program above:
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)
关于python - 按位循环右移,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/27176317/