【发布时间】：2016-11-02 01:14:51
【问题描述】：
我正在尝试在 Python 中使用 C 语言创建 exact 相同的 Mersenne Twister (MT)。
基于Lib/random.py以及阅读the docs，似乎整个MT是在_random中实现的，而_random是用C实现的：
The underlying implementation in C is both fast and threadsafe.
通过谷歌搜索“Python _random”，我找到了this page on GitHub，这似乎正是我正在寻找的东西，尽管它似乎不是官方的。
我使用了该源代码并剥离了除 MT 本身、种子函数和双重创建函数之外的所有内容。我还更改了一些类型，使整数为 32 位。
首先，这是许可证信息（为了安全起见）
/* Random objects */
/* ------------------------------------------------------------------
The code in this module was based on a download from:
http://www.math.keio.ac.jp/~matumoto/MT2002/emt19937ar.html
It was modified in 2002 by Raymond Hettinger as follows:
* the principal computational lines untouched.
* renamed genrand_res53() to random_random() and wrapped
in python calling/return code.
* genrand_int32() and the helper functions, init_genrand()
and init_by_array(), were declared static, wrapped in
Python calling/return code. also, their global data
references were replaced with structure references.
* unused functions from the original were deleted.
new, original C python code was added to implement the
Random() interface.
The following are the verbatim comments from the original code:
A C-program for MT19937, with initialization improved 2002/1/26.
Coded by Takuji Nishimura and Makoto Matsumoto.
Before using, initialize the state by using init_genrand(seed)
or init_by_array(init_key, key_length).
Copyright (C) 1997 - 2002, Makoto Matsumoto and Takuji Nishimura,
All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
1. Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in the
documentation and/or other materials provided with the distribution.
3. The names of its contributors may not be used to endorse or promote
products derived from this software without specific prior written
permission.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
Any feedback is very welcome.
http://www.math.keio.ac.jp/matumoto/emt.html
email: matumoto@math.keio.ac.jp
*/
/* ---------------------------------------------------------------*/
这是精简后的头文件（所有 Python 内容都已删除）。
mt.h：
#ifndef MT_H
#define MT_H
#include <stdint.h>
#define N 624
#define M 397
#define MATRIX_A 0x9908b0dfUL /* constant vector a */
#define UPPER_MASK 0x80000000UL /* most significant w-r bits */
#define LOWER_MASK 0x7fffffffUL /* least significant r bits */
typedef struct {
uint32_t state[N];
uint32_t index;
} RandomObject;
static uint32_t
genrand_int32(RandomObject *self)
{
uint32_t y;
static uint32_t mag01[2]={0x0UL, MATRIX_A};
/* mag01[x] = x * MATRIX_A for x=0,1 */
uint32_t *mt;
mt = self->state;
if (self->index >= N) { /* generate N words at one time */
uint32_t kk;
for (kk=0;kk<N-M;kk++) {
y = (mt[kk]&UPPER_MASK)|(mt[kk+1]&LOWER_MASK);
mt[kk] = mt[kk+M] ^ (y >> 1) ^ mag01[y & 0x1UL];
}
for (;kk<N-1;kk++) {
y = (mt[kk]&UPPER_MASK)|(mt[kk+1]&LOWER_MASK);
mt[kk] = mt[kk+(M-N)] ^ (y >> 1) ^ mag01[y & 0x1UL];
}
y = (mt[N-1]&UPPER_MASK)|(mt[0]&LOWER_MASK);
mt[N-1] = mt[M-1] ^ (y >> 1) ^ mag01[y & 0x1UL];
self->index = 0;
}
y = mt[self->index++];
y ^= (y >> 11);
y ^= (y << 7) & 0x9d2c5680UL;
y ^= (y << 15) & 0xefc60000UL;
y ^= (y >> 18);
return y;
}
static double
random_random(RandomObject *self)
{
uint32_t a=genrand_int32(self)>>5, b=genrand_int32(self)>>6;
return (double)((a*67108864.0+b)*(1.0/9007199254740992.0));
}
static void
init_genrand(RandomObject *self, uint32_t s)
{
uint32_t mti;
uint32_t *mt;
mt = self->state;
mt[0]= s & 0xffffffffUL;
for (mti=1; mti<N; mti++) {
mt[mti] =
(1812433253UL * (mt[mti-1] ^ (mt[mti-1] >> 30)) + mti);
/* See Knuth TAOCP Vol2. 3rd Ed. P.106 for multiplier. */
/* In the previous versions, MSBs of the seed affect */
/* only MSBs of the array mt[]. */
/* 2002/01/09 modified by Makoto Matsumoto */
mt[mti] &= 0xffffffffUL;
/* for >32 bit machines */
}
self->index = mti;
return;
}
#endif
这是一个主函数，它简单地创建一个 MT 对象，为其播种，然后吐出一个随机双精度数。
main.c
#include <stdio.h>
#include "mt.h"
int main() {
RandomObject rand;
init_genrand(&rand, 0x1234);
printf("%lf\n", random_random(&rand));
return 0;
}
输出为：0.279194。
这个想法是，当我在 python 中执行等效过程时，我会得到相同的随机数：
Python 2.7.12 (default, Jul 1 2016, 15:12:24)
[GCC 5.4.0 20160609] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import random
>>> random.seed(0x1234)
>>> random.random()
0.9281175899596723
当然，输出是不同的（或者我不会在这里问）。
我的问题是：我的程序有什么问题？我只是使用了错误的来源吗？我是否对 Python 对 C 返回的值做了哪些错误的假设？
老实说，我对 Python 了解不多，所以我可能在某个地方犯了一个愚蠢的错误。
【问题讨论】：
-
即使你得到这个工作，RNG 的细节可能会从 Python 版本更改为 Python。你考虑过只用 C 调用 python 吗？
-
@Schwern 我正在“攻击” MT（即演示为什么它不适合 crypt 使用）。我想专门为 python MT 做这个。源代码似乎是一个非常好的起点，因为我自己的实现也没有提供相同的输出。
-
在那种情况下，没有像样的 MT 库吗？或者，将 Python 嵌入到 C 中。这样您就不必翻译，而是在攻击原始代码。 docs.python.org/2/extending/embedding.html