Hi Peter,
>> static inline uint64_t d2_64(uint64_t v)
>> {
>> uint64_t mask = v & 0x0101010101010101U;
>> mask = (mask << 8) - mask;
>
> (mask << 7) I assume...
No. It's "(mask << 8) - mask". We want to expand the bit at position 0
(in each byte) to the full byte, resulting in 0xFF if the bit is at 1,
and 0x00 if the bit is 0.
(0 << 8) - 0 = 0x00
(1 << 8) - 1 = 0x100 - 1 = 0xFF
Ciao,
Andrea
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