RFR: 8341470: BigDecimal.stripTrailingZeros() optimization [v33]

[Raffaello Giulietti]

On Wed, 9 Oct 2024 15:18:15 GMT, fabioromano1 <duke at openjdk.org> wrote:

>> An optimized algorithm for `BigDecimal.stripTrailingZeros()` that uses repeated squares trick.
>
> fabioromano1 has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Store log5(2) in BigDecimal

src/java.base/share/classes/java/math/BigDecimal.java line 5260:

> 5258:         // a multiple of 10^n must be a multiple of 2^n
> 5259:         int powsOf2 = intVal.getLowestSetBit();
> 5260:         long remainingZeros = Math.min(scale - preferredScale, powsOf2);

Please document the semantics of this variable, preferably in maths, like inequalities, etc.

src/java.base/share/classes/java/math/BigDecimal.java line 5270:

> 5268:         intVal = intVal.shiftRight(powsOf2); // remove powers of 2
> 5269:         // maxPowsOf5 == ceil(log5(intVal)) roughly
> 5270:         long maxPowsOf5 = (long) Math.ceil(intVal.bitLength() * LOG_5_OF_2);

Please document the meaning of this variable in form of inequalities w.r.t. `intVal`.
Also, shouldn't it be named `maxExpOf5` or similar? It's an exponent, after all.

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PR Review Comment: https://git.openjdk.org/jdk/pull/21323#discussion_r1795743150
PR Review Comment: https://git.openjdk.org/jdk/pull/21323#discussion_r1795743514