I want to create a bitmask for the most right continuous range of set bits. For example 01010110 -> 00000110. Is (x & ~(x + (x & -x))) the best way to do that or is there a better solution? #followerpower
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Bit scan instructions, obviously, if it doesn't need to be portable. Other than that, maybe http://webpages.charter.net/tlikens/tech/bitmaps/bit_popcnt.html … could be a source of inspiration?
Can you give an example for how to implement that more efficiently using bit scan instructions? I can't seem to be able to build something more efficient. (Even if I assume ctz(0)/clz(0) to be defined.)
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CTZ/shift right/inverse/CTZ. Not sure if this is more efficient, but maybe worth looking into.
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That doesn’t give a mask. You’ll still need to clear the other bits of the res2, for example, shifting it left by XLEN-res4 and then right by XLEN-res1. All of which takes five more instructions.
End of conversation
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