RC6加密C语言的例子，可以直接C编译器编译可以直接通过

#include <stdio.h>
  
#define w 32    /* word为32bits */
#define r 20    //加密轮数

#define P32 0xB7E15163    　　/* 定义两个常量，用于子密钥生成 */
#define Q32 0x9E3779B9

#define bytes   (w / 8)                        /* 定义字节*/
#define c       ((b + bytes - 1) / bytes)      /* 密钥字数 */
#define R24     (2 * r + 4)
#define lgw     5                           /* log2(w)  */

/* 定义逻辑移位操作运算 */
#define ROTL(x,y) (((x)<<(y&(w-1))) | ((x)>>(w-(y&(w-1)))))
#define ROTR(x,y) (((x)>>(y&(w-1))) | ((x)<<(w-(y&(w-1)))))

unsigned int S[R24 - 1];                    /* 子密钥组 */

void rc6_key_setup(unsigned char *K, int b)
{
    int i, j, s, v;
    unsigned int L[(32 + bytes - 1) / bytes]; /* Big enough for max b */
    unsigned int A, B;

    L[c - 1] = 0;
    for (i = b - 1; i >= 0; i--)
        L[i / bytes] = (L[i / bytes] << 8) + K[i];

    S[0] = P32;
    for (i = 1; i <= 2 * r + 3; i++)
        S[i] = S[i - 1] + Q32;

    A = B = i = j = 0;
    v = R24;
    if (c > v) v = c;
    v *= 3;

    for (s = 1; s <= v; s++)
    {
        A = S[i] = ROTL(S[i] + A + B, 3);
        B = L[j] = ROTL(L[j] + A + B, A + B);
        i = (i + 1) % R24;
        j = (j + 1) % c;
    }
}

void rc6_block_encrypt(unsigned int *pt, unsigned int *ct)
{
    unsigned int A, B, C, D, t, u, x;
    int i;

    A = pt[0];
    B = pt[1];
    C = pt[2];
    D = pt[3];
    B += S[0];
    D += S[1];
    for (i = 2; i <= 2 * r; i += 2)
    {
        t = ROTL(B * (2 * B + 1), lgw);
        u = ROTL(D * (2 * D + 1), lgw);
        A = ROTL(A ^ t, u) + S[i];
        C = ROTL(C ^ u, t) + S[i + 1];
        x = A;
        A = B;
        B = C;
        C = D;
        D = x;
    }
    A += S[2 * r + 2];
    C += S[2 * r + 3];
    ct[0] = A;
    ct[1] = B;
    ct[2] = C;
    ct[3] = D;
}

void rc6_block_decrypt(unsigned int *ct, unsigned int *pt)
{
    unsigned int A, B, C, D, t, u, x;
    int i;

    A = ct[0];
    B = ct[1];
    C = ct[2];
    D = ct[3];
    C -= S[2 * r + 3];
    A -= S[2 * r + 2];
    for (i = 2 * r; i >= 2; i -= 2)
    {
        x = D;
        D = C;
        C = B;
        B = A;
        A = x;
        u = ROTL(D * (2 * D + 1), lgw);
        t = ROTL(B * (2 * B + 1), lgw);
        C = ROTR(C - S[i + 1], t) ^ u;
        A = ROTR(A - S[i], u) ^ t;
    }
    D -= S[1];
    B -= S[0];
    pt[0] = A;
    pt[1] = B;
    pt[2] = C;
    pt[3] = D;    
}

struct test_struct
{
    int keylen;
    unsigned char key[32];
    unsigned int pt[4];
    unsigned int ct[4];
} tests[] =
{
    { 16,   {0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
         0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00},
        {0x00000000, 0x00000000, 0x00000000, 0x00000000},
        {0x36a5c38f, 0x78f7b156, 0x4edf29c1, 0x1ea44898},
    },

    { 16,   {0x01, 0x23, 0x45, 0x67, 0x89, 0xab, 0xcd, 0xef,
         0x01, 0x12, 0x23, 0x34, 0x45, 0x56, 0x67, 0x78},
        {0x35241302, 0x79685746, 0xbdac9b8a, 0xf1e0dfce},
        {0x2f194e52, 0x23c61547, 0x36f6511f, 0x183fa47e},
    },

    { 24,   {0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
         0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
         0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00},
        {0x00000000, 0x00000000, 0x00000000, 0x00000000},
        {0xcb1bd66c, 0x38300b19, 0x163f8a4e, 0x82ae9086},
    },

    { 24,   {0x01, 0x23, 0x45, 0x67, 0x89, 0xab, 0xcd, 0xef,
         0x01, 0x12, 0x23, 0x34, 0x45, 0x56, 0x67, 0x78,
         0x89, 0x9a, 0xab, 0xbc, 0xcd, 0xde, 0xef, 0xf0},
        {0x35241302, 0x79685746, 0xbdac9b8a, 0xf1e0dfce},
        {0xd0298368, 0x0405e519, 0x2ae9521e, 0xd49152f9},
    },

    { 32,   {0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
         0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
         0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
         0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00},
        {0x00000000, 0x00000000, 0x00000000, 0x00000000},
        {0x05bd5f8f, 0xa85fd110, 0xda3ffa93, 0xc27e856e},
    },

    { 32,   {0x01, 0x23, 0x45, 0x67, 0x89, 0xab, 0xcd, 0xef,
         0x01, 0x12, 0x23, 0x34, 0x45, 0x56, 0x67, 0x78,
         0x89, 0x9a, 0xab, 0xbc, 0xcd, 0xde, 0xef, 0xf0,
         0x10, 0x32, 0x54, 0x76, 0x98, 0xba, 0xdc, 0xfe},
        {0x35241302, 0x79685746, 0xbdac9b8a, 0xf1e0dfce},
        {0x161824c8, 0x89e4d7f0, 0xa116ad20, 0x485d4e67},
    },

    {       0,
    }
};

int
main()
{
    unsigned int ct[4], pt[4];
    int i,j;
    struct test_struct *p;

    for (p = tests, i = 1; p->keylen; p++, i++)
    {
        rc6_key_setup(p->key, p->keylen);
        rc6_block_encrypt(p->pt, ct);
        printf("Test   %d\n",i);

        printf("密钥是%d字:\n密钥为:",p->keylen);
        for(j=0;j<p->keylen;j++)
            printf("%.8lx ",p->key[j]);
        printf("\n");
        printf("加密:\n明文：%08x %08x %08x %08x\n",
            p->pt[0], p->pt[1], p->pt[2], p->pt[3]);
        printf("密文: %08x %08x %08x %08x\n",
            ct[0], ct[1], ct[2], ct[3]);
        rc6_block_decrypt(ct, pt);
        printf("解密:\n密文：%08x %08x %08x %08x\n",
            ct[0], ct[1], ct[2], ct[3]);
        printf("明文: %08x %08x %08x %08x\n\n",
            pt[0], pt[1], pt[2], pt[3]);
    }
    system("pause");
    return 0;
    
}