Python调用C的方法

参考：http://www.cnblogs.com/fxjwind/archive/2011/07/05/2098636.html

         http://amazingjxq.com/2012/01/09/python%E8%B0%83%E7%94%A8c%E5%87%BD%E6%95%B0/

 >>>cd /home/jxq/code/

gcc -fPIC -shared bob_hash.c -o bob_hash.so

然后在python里面用ctypes加载刚才的动态库。argtypes和restype分别对应函数的参数和返回值的类型。这样就可以直接调用了。

>>> from ctypes import CDLL, c_int, c_void_p
>>> bob_hash = CDLL('/home/jxq/code/bob_hash.so')
>>> hash_string = bob_hash.hash_string
>>> hash_string.argtypes = [c_void_p]
>>> hash_string.restype = c_int
>>> hash_string('123')

代码：

#include <stdio.h>
#include <string.h>
#define mix(a,b,c)                              
    {                                          
        a -= b; a -= c; a ^= (c >> 13);        
        b -= c; b -= a; b ^= (a << 8);          
        c -= a; c -= b; c ^= (b >> 13);        
        a -= b; a -= c; a ^= (c >> 12);        
        b -= c; b -= a; b ^= (a << 16);        
        c -= a; c -= b; c ^= (b >> 5);          
        a -= b; a -= c; a ^= (c >> 3);          
        b -= c; b -= a; b ^= (a << 10);        
        c -= a; c -= b; c ^= (b >> 15);        
    }

unsigned int bob_hash(void *val, unsigned int length)
{
    char *k = (char *)val;
    unsigned long a,b,c,len;

    /* Set up the internal state */
    len = length;
    a = b = c = 0x9e3779b9;  /* the golden ratio; an arbitrary value */

    /* Handle most of the key */
    while (len >= 12)
    {
        a += (k[0] +((unsigned long)k[1] << 8) +((unsigned long)k[2] << 16) +((unsigned long)k[3] << 24));
        b += (k[4] +((unsigned long)k[5] << 8) +((unsigned long)k[6] << 16) +((unsigned long)k[7] << 24));
        c += (k[8] +((unsigned long)k[9] << 8) +((unsigned long)k[10]<< 16)+((unsigned long)k[11] << 24));
        mix(a,b,c);
        k += 12; len -= 12;
    }

    /* Handle the last 11 bytes */
    c += length;
    switch(len)              /* all the case statements fall through */
    {
    case 11: c+=((unsigned long)k[10] << 24);
    case 10: c+=((unsigned long)k[9]  << 16);
    case 9 : c+=((unsigned long)k[8]  << 8);
        /* the first byte of c is reserved for the length */
    case 8 : b+=((unsigned long)k[7] << 24);
    case 7 : b+=((unsigned long)k[6] << 16);
    case 6 : b+=((unsigned long)k[5] << 8);
    case 5 : b+=k[4];
    case 4 : a+=((unsigned long)k[3] << 24);
    case 3 : a+=((unsigned long)k[2] << 16);
    case 2 : a+=((unsigned long)k[1] << 8);
    case 1 : a+=k[0];
    }
    mix(a,b,c);

    return c;
}

int hash_string(void *tmpstr)
{
    int hash = (int)bob_hash(tmpstr, strlen(tmpstr));
    if(hash < 0)
    {
        hash = -hash;
    }
    return (int)(hash % 200);
}