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Less-than comparison with a constant - #318

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msoeken/arithmetic
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Less-than comparison with a constant#318
Mathias Soeken (msoeken) wants to merge 19 commits into
mainfrom
msoeken/arithmetic

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@msoekenMathias Soeken (msoeken) commented Aug 31, 2020

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This operation implements an optimised version of Fig. 17 in arXiv:1902.02134. Constant input bits are propagated into the circuits, and no qubits are allocated for them. Further optimisations are applied for trailing 0s in the bit representation of the constant. The circuit uses AND gates instead of Toffoli gates to further reduce costs.

API review is necessary for consistent naming of arithmetic operations (e.g., compare to CompareUsingRippleCarry which performs greater-than comparison.)

@msoekenMathias Soeken (msoeken) added the Status-NeedsApiReview This PR requires an API review before merging in. label Aug 31, 2020
cgranade
Cassandra Granade (cgranade) reviewed Sep 1, 2020
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@cgranadeCassandra Granade (cgranade) left a comment

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Looks good to me, modulo a few comments here and there. Happy to approve once we complete API review. Thanks!

Comment threadStandard/tests/ArithmeticTests.qs Outdated
Comment threadStandard/src/Arithmetic/Arithmetic.qs
Comment threadStandard/src/Arithmetic/Comparators.qs Outdated
Comment threadStandard/src/Arithmetic/Comparators.qs Outdated
Comment threadStandard/src/Arithmetic/Comparators.qs Outdated
Comment threadStandard/src/Arithmetic/Comparators.qs Outdated
Comment threadStandard/src/Arithmetic/Comparators.qs Outdated
/// Dominic W. Berry, Craig Gidney, Mario Motta, Jarrod R. McClean, Ryan Babbush
/// Quantum 3, 208 (2019)
/// https://arxiv.org/abs/1902.02134v4
operation LessThanConstantUsingRippleCarry(c : BigInt, x : LittleEndian, output : Qubit)

@cgranadeCassandra Granade (cgranade)Sep 1, 2020

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We can defer to API review, but I'd suggest maybe something like "CompareLessThanConstantUsingRippleCarry"?

@msoekenMathias Soeken (msoeken)Sep 2, 2020

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Sounds good, but we need further discussion because we also have CompareUsingRippleCarry at the moment.

@cgranadeCassandra Granade (cgranade)Sep 2, 2020

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Good point; that can definitely create some confusion. Agreed with the need for further discussion.

@msoeken

Mathias Soeken (msoeken) commented Sep 2, 2020

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Thanks for your feedback Cassandra Granade (@cgranade), I have incorporated your comments.

@microsoft-github-updates
microsoft-github-updatesBot changed the base branch from master to mainSeptember 9, 2020 07:52
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