请用c++实现SM3签名算法

SM3是一种密码学哈希函数，不是签名算法。但是，可以使用SM3来实现数字签名算法。以下是使用C++实现SM3哈希函数的示例代码：

#include <iostream>
#include <cstring>
#include <cstdint>
#include <iomanip>

using namespace std;

const uint32_t T[] = {
    0x79cc4519, 0xf3988a32, 0xe7311465, 0xce6228cb,
    0x9c4ba83b, 0x3faba35e, 0x7c5f4910, 0x1e8bbf20
};

const uint32_t IV[] = {
    0x7380166f, 0x4914b2b9, 0x172442d7, 0xda8a0600,
    0xa96f30bc, 0x163138aa, 0xe38dee4d, 0xb0fb0e4e
};

const uint32_t SM3_BLOCK_SIZE = 64; // 512 bits
const uint32_t SM3_DIGEST_SIZE = 32; // 256 bits

void sm3_transform(uint32_t digest[], const uint8_t block[])
{
    uint32_t W[68], W1[64];
    uint32_t A, B, C, D, E, F, G, H, SS1, SS2, TT1, TT2;
    int j;

    const uint32_t *p = (const uint32_t*)block;
    for (j = 0; j < 16; j++) {
        W[j] = p[j];
    }
    for (j = 16; j < 68; j++) {
        W[j] = W[j-16] ^ W[j-9] ^ (W[j-3] << 15) ^ (W[j-13] >> 7) ^ W[j-6];
    }
    for (j = 0; j < 64; j++) {
        W1[j] = W[j] ^ W[j+4];
    }

    A = digest[0];
    B = digest[1];
    C = digest[2];
    D = digest[3];
    E = digest[4];
    F = digest[5];
    G = digest[6];
    H = digest[7];

    for (j = 0; j < 16; j++) {
        SS1 = (A << 12) + E + T[j];
        SS1 = (SS1 << 7) | (SS1 >> 25);
        SS2 = SS1 ^ (A << 12);
        TT1 = (FF0(A, B, C) + D + SS2 + W1[j]);
        TT2 = (GG0(E, F, G) + H + SS1 + W[j]);
        D = C;
        C = (B << 9) | (B >> 23);
        B = A;
        A = TT1;
        H = G;
        G = (F << 19) | (F >> 13);
        F = E;
        E = P0(TT2);
    }
    for (j = 16; j < 64; j++) {
        SS1 = (A << 12) + E + T[j];
        SS1 = (SS1 << 7) | (SS1 >> 25);
        SS2 = SS1 ^ (A << 12);
        TT1 = (FF1(A, B, C) + D + SS2 + W1[j]);
        TT2 = (GG1(E, F, G) + H + SS1 + W[j]);
        D = C;
        C = (B << 9) | (B >> 23);
        B = A;
        A = TT1;
        H = G;
        G = (F << 19) | (F >> 13);
        F = E;
        E = P0(TT2);
    }

    digest[0] ^= A;
    digest[1] ^= B;
    digest[2] ^= C;
    digest[3] ^= D;
    digest[4] ^= E;
    digest[5] ^= F;
    digest[6] ^= G;
    digest[7] ^= H;
}

void sm3_init(uint32_t digest[])
{
    memcpy(digest, IV, SM3_DIGEST_SIZE);
}

void sm3_update(uint32_t digest[], const uint8_t data[], uint32_t len, uint32_t *total)
{
    uint32_t left = (*total) & (SM3_BLOCK_SIZE - 1);
    uint32_t fill = SM3_BLOCK_SIZE - left;

    *total += len;

    if (left && len >= fill) {
        memcpy((void *)(digest + left / 4), data, fill);
        sm3_transform(digest, (const uint8_t *)digest);
        data += fill;
        len -= fill;
        left = 0;
    }

    while (len >= SM3_BLOCK_SIZE) {
        sm3_transform(digest, data);
        data += SM3_BLOCK_SIZE;
        len -= SM3_BLOCK_SIZE;
    }

    if (len > 0) {
        memcpy((void *)(digest + left / 4), data, len);
    }
}

void sm3_final(uint32_t digest[], const uint8_t *data, uint32_t len, uint32_t total)
{
    uint8_t block[SM3_BLOCK_SIZE];
    uint32_t left = total & (SM3_BLOCK_SIZE - 1);
    uint32_t last = SM3_BLOCK_SIZE - left;

    memcpy(block, data, len);
    block[len] = 0x80;
    if (last < 8) {
        memset(block + len + 1, 0, last - 1);
        sm3_update(digest, block, SM3_BLOCK_SIZE, &total);
        memset(block, 0, SM3_BLOCK_SIZE - 8);
    } else {
        memset(block + len + 1, 0, last - 1 - 8);
    }
    total <<= 3;
    for (int i = 0; i < 8; i++) {
        block[SM3_BLOCK_SIZE - 1 - i] = (total >> (i * 8)) & 0xff;
    }
    sm3_update(digest, block, SM3_BLOCK_SIZE, &total);
}

int main()
{
    uint8_t msg[] = "hello world";
    uint32_t digest[SM3_DIGEST_SIZE / 4];
    uint32_t total = 0;

    sm3_init(digest);
    sm3_update(digest, msg, strlen((char*)msg), &total);
    sm3_final(digest, msg, strlen((char*)msg), total);

    cout << "SM3 hash of message \"hello world\": " << endl;
    for (int i = 0; i < SM3_DIGEST_SIZE / 4; i++) {
        cout << hex << setfill('0') << setw(8) << digest[i];
    }
    cout << endl;

    return 0;
}

需要注意的是，这个示例代码只是演示了如何使用C++实现SM3哈希函数，而不是数字签名算法。如果需要实现SM3数字签名算法，还需要使用公钥、私钥等相关参数。