Minor optimization for Fractions.limit_denominator #93730
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When we construct the upper and lower candidates in limit_denominator, the numerator and denominator are already relatively prime (and the denominator positive) by construction, so there's no need to go through the usual normalisation in the constructor. This saves a couple of potentially expensive gcd calls. Suggested by Michael Scott Asato Cuthbert in pythonGH-93477.
rhettinger
approved these changes
Jun 11, 2022
rhettinger
reviewed
Jun 11, 2022
Lib/fractions.py
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| bound1 = Fraction(p0+k*p1, q0+k*q1) | ||
| bound2 = Fraction(p1, q1) | ||
| bound1 = Fraction(p0+k*p1, q0+k*q1, _normalize=False) | ||
| bound2 = Fraction(p1, q1, _normalize=False) | ||
| if abs(bound2 - self) <= abs(bound1-self): |
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While you're here, can you fix-up the spacing around the operator on line 252?
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Now ready for review. @mscuthbert: If you have a moment, please could you take a look at this and let me know whether it meets your needs? |
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Thank you @mdickinson a ton! |
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When we construct the upper and lower candidates in limit_denominator, the numerator and denominator are already relatively prime (and the denominator positive) by construction, so there's no need to go through the usual normalisation in the constructor. This saves a couple of potentially expensive gcd calls.
We also replace the comparison used to determine which bound to pick with a simpler and faster version.
Inspired by Michael Scott Asato Cuthbert in GH-93477.