https://github.com/D-Programming-Language/druntime/blob/master/src/core/bitop.d

Alıntı ("Sample"):

>
> int popcnt( uint x ) pure {
>     // Avoid branches, and the potential for cache misses which
>     // could be incurred with a table lookup.
>
>     // We need to mask alternate bits to prevent the
>     // sum from overflowing.
>     // add neighbouring bits. Each bit is 0 or 1.
>     x = x - ((x>>1) & 0x5555_5555);
>     // now each two bits of x is a number 00,01 or 10.
>     // now add neighbouring pairs
>     x = ((x&0xCCCC_CCCC)>>2) + (x&0x3333_3333);
>     // now each nibble holds 0000-0100. Adding them won't
>     // overflow any more, so we don't need to mask any more
>
>     // Now add the nibbles, then the bytes, then the words
>     // We still need to mask to prevent double-counting.
>     // Note that if we used a rotate instead of a shift, we
>     // wouldn't need the masks, and could just divide the sum
>     // by 8 to account for the double-counting.
>     // On some CPUs, it may be faster to perform a multiply.
>
>     x += (x>>4);
>     x &= 0x0F0F_0F0F;
>     x += (x>>8);
>     x &= 0x00FF_00FF;
>     x += (x>>16);
>     x &= 0xFFFF;
>     return x;
>
> } unittest {
>
>     assert( popcnt( 0 ) == 0 );
>     assert( popcnt( 7 ) == 3 );
>     assert( popcnt( 0xAA )== 4 );
>     assert( popcnt( 0x8421_1248 ) == 8 );
>     assert( popcnt( 0xFFFF_FFFF ) == 32 );
>     assert( popcnt( 0xCCCC_CCCC ) == 16 );
>     assert( popcnt( 0x7777_7777 ) == 24 );
> }
> ```

>

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