ndigits with negative base: error out instead of giving incorrect result #29148
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Because of an unchecked conversion via `signed` (instead of `Signed`), we were giving wrong results, e.g. we had `ndigits(typemax(UInt), base=-2) != ndigits(big(typemax(UInt)), base=-2)`
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What label would fit here? I would say "math" would be the closest, but not quite... |
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Could we just give the correct answer here? Maybe by widening to a larger type? It may also be possible to tweak this computation for negative bases somehow instead. |
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So, I think this definition might work: ndigits0znb(x::Unsigned, b::Integer) = ndigits0znb(-signed(fld(x, -b)), b) + (x != 0)It relies on the fact that |
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Oh I was too lazy, but your idea is clever! I pushed it here to launch CI, but please re-commit in your name! |
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KristofferC
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It relies on the fact that `cld(x, b) == -fld(x, -b)` but does the conversion from unsigned to signed before negating the unsigned quotient; since `-b ≥ 2` the quotient always fits in the signed type. (cherry picked from commit 77ec1ec)
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KristofferC
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Feb 11, 2019
It relies on the fact that `cld(x, b) == -fld(x, -b)` but does the conversion from unsigned to signed before negating the unsigned quotient; since `-b ≥ 2` the quotient always fits in the signed type. (cherry picked from commit 77ec1ec)
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Because of an unchecked conversion via
signed(instead ofSigned),we were giving wrong results, e.g. we had
ndigits(typemax(UInt), base=-2) != ndigits(big(typemax(UInt)), base=-2)