RFR: 8356891: Some code simplifications for basic BigIntegers' bit operations

[fabioromano1]

On Sun, 11 May 2025 16:00:55 GMT, Chen Liang <liach at openjdk.org> wrote:

> This should really be refactored to an instance method `bitLengthUnsigned` or `magBitCount`

I would prefer `magBitLength` as a name, since `bitCount` is usually referred to one's bit count. But before do this, I'd hear the opinion of @rgiulietti about that.

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PR Review Comment: https://git.openjdk.org/jdk/pull/25166#discussion_r2083563140