check before operator #13290

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version: 0.16.0 source: /src/arith_uint256.cpp line 179 : if (pn[pos] & 1 << nbits)

when ( pn[pos] & 1) =1 and nbits = 31, can result in overflow

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Why?

the operation '<<' on signed integer cam result in overlow when the left operand's value is '1' and the right operand's(nbits) value is '31'

This is unsigned integer math, as indicated in the class and file names.

@Empact No, this is in the internal implementation of uint256; the type of pn[pos] is uint32_t. @wudigithub1 The expression pn[pos] & 1 is uint32_t, which is unsigned so shifting up by 31 bits is fine.

I suggest closing this issue, since it seems to be a bug in the static analyser.

@sipa yes we're in agreement. The underlying data is unsigned so the concern does not apply.

thanks，i understand and close the issue