如何使用向量化解決方案提高IP位址解析速度？-C++-PHP中文網

如何使用向量化解決方案提高IP位址解析速度？

Barbara Streisand

發布： 2024-11-15 04:24:02

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How to improve IP address parsing speed using vectorized solutions?

提高 IP 位址解析速度

您目前解析 IPv4 位址的程式碼相當高效，但可以進一步最佳化以獲得更快的速度。一種方法是利用專為此任務設計的向量化解決方案。

用於快速IPv4 解析的向量化解決方案

對於支援SSE4.1 或SSSE3 指令的x86 處理器，這裡有一個可顯著提高效能的向量化解決方案:

__m128i shuffleTable[65536];    //can be reduced 256x times, see @IwillnotexistIdonotexist

UINT32 MyGetIP(const char *str) {
    __m128i input = _mm_lddqu_si128((const __m128i*)str);   //"192.167.1.3"
    input = _mm_sub_epi8(input, _mm_set1_epi8('0'));        //1 9 2 254 1 6 7 254 1 254 3 208 245 0 8 40 
    __m128i cmp = input;                                    //...X...X.X.XX...  (signs)
    UINT32 mask = _mm_movemask_epi8(cmp);                   //6792 - magic index
    __m128i shuf = shuffleTable[mask];                      //10 -1 -1 -1 8 -1 -1 -1 6 5 4 -1 2 1 0 -1 
    __m128i arr = _mm_shuffle_epi8(input, shuf);            //3 0 0 0 | 1 0 0 0 | 7 6 1 0 | 2 9 1 0 
    __m128i coeffs = _mm_set_epi8(0, 100, 10, 1, 0, 100, 10, 1, 0, 100, 10, 1, 0, 100, 10, 1);
    __m128i prod = _mm_maddubs_epi16(coeffs, arr);          //3 0 | 1 0 | 67 100 | 92 100 
    prod = _mm_hadd_epi16(prod, prod);                      //3 | 1 | 167 | 192 | ? | ? | ? | ?
    __m128i imm = _mm_set_epi8(-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 6, 4, 2, 0);
    prod = _mm_shuffle_epi8(prod, imm);                     //3 1 167 192 0 0 0 0 0 0 0 0 0 0 0 0
    return _mm_extract_epi32(prod, 0);
//  return (UINT32(_mm_extract_epi16(prod, 1)) << 16) + UINT32(_mm_extract_epi16(prod, 0)); //no SSE 4.1
}

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隨機表預計算

要有效地利用此向量化解決方案，需要一個預先計算的隨機表shuffleTable，可以如下產生：

void MyInit() {
    memset(shuffleTable, -1, sizeof(shuffleTable));
    int len[4];
    for (len[0] = 1; len[0] <= 3; len[0]++)
        for (len[1] = 1; len[1] <= 3; len[1]++)
            for (len[2] = 1; len[2] <= 3; len[2]++)
                for (len[3] = 1; len[3] <= 3; len[3]++) {
                    int slen = len[0] + len[1] + len[2] + len[3] + 4;
                    int rem = 16 - slen;
                    for (int rmask = 0; rmask < 1<<rem; rmask++) {
//                    { int rmask = (1<<rem)-1;    //note: only maximal rmask is possible if strings are zero-padded
                        int mask = 0;
                        char shuf[16] = {-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1};
                        int pos = 0;
                        for (int i = 0; i < 4; i++) {
                            for (int j = 0; j < len[i]; j++) {
                                shuf[(3-i) * 4 + (len[i]-1-j)] = pos;
                                pos++;
                            }
                            mask ^= (1<<pos);
                            pos++;
                        }
                        mask ^= (rmask<<slen);
                        _mm_store_si128(&amp;shuffleTable[mask], _mm_loadu_si128((__m128i*)shuf));
                    }
                }
}

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