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Return ±1 from (-1).Pow for an integer power beyond double range [patch] - #136
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Pow special-cased a base of One but not NegativeOne, so (-1)^n for an
integer n outside the range of a double fell through to PowByLogarithm,
computed 0 * infinity = NaN and threw OverflowException("The result is
too small to represent."). (-1)^n is exact for any integer n, so return
One for an even power and NegativeOne for an odd one, decided on the
PreciseNumber without going through a double. A non-integer power of -1
still throws ArgumentException.
Fixes #117
Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01MiwudJMQgsVwkkrRfMfwG2
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Fixes #117
What was wrong
Powspecial-cased a base ofOnebut notNegativeOne. For an integer power outside the range of a double,(-1)^nfell through toPowByLogarithm, which computed0 · ∞ = NaNand threwOverflowException("The result is too small to represent.").Change
Next to the
Equal(this, One)check, a base of -1 with an integer power now returnsOnefor an even power andNegativeOnefor an odd one. The parity check works on thePreciseNumberdirectly, so it never goes through a double. A non-integer power of -1 still throwsArgumentException, as before.Tests
In
SignificantNumberRangeTests:Pow_NegativeOneToAnEvenIntegerBeyondDoubleRange_ReturnsOnecovers2E308,-1E400,-3E400, and1E308, which is still inside double range.Pow_NegativeOneToAnOddIntegerBeyondDoubleRange_ReturnsNegativeOnecovers2…(310 zeros)…1and its negation.Pow_NegativeOneToANonIntegerPower_StillThrowsArgumentExceptionWith the library change reverted, 4 of these fail: the three out-of-range even rows and the odd test. With the change, the full suite passes locally on net10.0 (190/190).
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