popcnt.cpp
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static const unsigned char g_pop_cnt[256] = |
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{ |
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# define B2(n) n, n+1, n+1, n+2 |
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# define B4(n) B2(n), B2(n+1), B2(n+1), B2(n+2) |
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# define B6(n) B4(n), B4(n+1), B4(n+1), B4(n+2) |
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B6(0), B6(1), B6(1), B6(2) |
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}; |
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|
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static unsigned int POPCNT_Table(const unsigned char * buf, unsigned int len) { |
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unsigned int cnt = 0; |
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unsigned int ndwords = len / 4; |
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for(; ndwords; ndwords--) {
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unsigned int v = *(unsigned int*)buf; |
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cnt += g_pop_cnt[v & 0xff] +
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g_pop_cnt[(v >> 8) & 0xff] + |
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g_pop_cnt[(v >> 16) & 0xff] + |
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g_pop_cnt[v >> 24];
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buf += 4;
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} |
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if (len & 2) { |
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unsigned int v = *(short*)buf; |
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cnt += g_pop_cnt[ v & 0xff ] +
|
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g_pop_cnt[ v >> 8 ];
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buf += 2;
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} |
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if (len & 1) |
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cnt += g_pop_cnt[ *buf ]; |
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return cnt;
|
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} |
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|
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int main(int argc, char const *argv[]) |
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{ |
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unsigned int value = 1; |
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for (unsigned int i = 0; i < 262151000; i++) { |
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unsigned int res = POPCNT_Table((unsigned char*)&i, 4); |
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} |
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return 0; |
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} |