53 lines
1.0 KiB
C++
53 lines
1.0 KiB
C++
namespace factor
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{
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inline cell log2(cell x)
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{
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cell n;
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#if defined(FACTOR_X86) || defined(FACTOR_AMD64)
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asm ("bsr %1, %0;":"=r"(n):"r"(x));
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#elif defined(FACTOR_PPC)
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asm ("cntlzw %1, %0;":"=r"(n):"r"(x));
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n = (31 - n);
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#else
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#error Unsupported CPU
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#endif
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return n;
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}
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inline cell rightmost_clear_bit(cell x)
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{
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return log2(~x & (x + 1));
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}
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inline cell rightmost_set_bit(cell x)
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{
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return log2(x & -x);
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}
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inline cell popcount(cell x)
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{
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#ifdef FACTOR_64
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u64 k1 = 0x5555555555555555ll;
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u64 k2 = 0x3333333333333333ll;
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u64 k4 = 0x0f0f0f0f0f0f0f0fll;
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u64 kf = 0x0101010101010101ll;
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cell ks = 56;
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#else
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u32 k1 = 0x55555555;
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u32 k2 = 0x33333333;
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u32 k4 = 0xf0f0f0f;
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u32 kf = 0x1010101;
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cell ks = 24;
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#endif
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x = x - ((x >> 1) & k1); // put count of each 2 bits into those 2 bits
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x = (x & k2) + ((x >> 2) & k2); // put count of each 4 bits into those 4 bits
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x = (x + (x >> 4)) & k4 ; // put count of each 8 bits into those 8 bits
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x = (x * kf) >> ks; // returns 8 most significant bits of x + (x<<8) + (x<<16) + (x<<24) + ...
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return x;
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}
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}
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