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Twice faster Jacobian quotients #13

Merged
merged 9 commits into from
Aug 6, 2022
Merged

Twice faster Jacobian quotients #13

merged 9 commits into from
Aug 6, 2022

Commits on Aug 5, 2022

  1. Move surface isogeny tests to a separate file

    @remyoudompheng
    remyoudompheng committed Aug 5, 2022
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  2. Factor out and accelerate Richelot correspondence 

    This makes FromJacToJac about 50% faster, mostly from
avoiding switching rings and variable substitutions,
and computing manually the expansion as symmetric functions.
    @remyoudompheng
    remyoudompheng committed Aug 5, 2022
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  3. Remove costly no-op calls in Coefficient 

    The polynomial argument is no longer an element
of the fraction field.
    @remyoudompheng
    remyoudompheng committed Aug 5, 2022
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  4. Add hints when constructing 3-isogenies 

    The point is already known to be of order 3 so providing
information to the constructor avoids unnecessary work.
    @remyoudompheng
    remyoudompheng committed Aug 5, 2022
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  5. Rebalance precomputed powers in FromJacToJac 

    The cost of apply the Richelot isogeny determines how many
precomputed Jacobian point powers are worth keeping between
FromJacToJac iterations.

Since the image computation is now twice faster, we can
pass around a second precomputed power to keep balance.
    @remyoudompheng
    remyoudompheng committed Aug 5, 2022
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  6. Implement a local specialized version of Jacobian doubling 

    This allows for minor simplifications and is about 10% faster.
    @remyoudompheng
    remyoudompheng committed Aug 5, 2022
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  7. Get rid of most calls to monic() 

    SAGE monic() method on polynomials is very generic and
often slow due to going through many layers of Python objects.

It turns out that all Jacobian doubling formulas are also
compatible with non-monic Mumford coordinates so relaxing that
constraint saves some operations and accelerates computation
by about 10%.
    @remyoudompheng
    remyoudompheng committed Aug 5, 2022
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  8. Slightly simpler computation of H polynomials 

    Looking carefully at the coefficients of polynomials H1,H2,H3
they turn out to be almost exactly the coefficients of the inverse
matrix. This removes some redundant computations as the determinant
computation needs very similar operations.
    @remyoudompheng
    remyoudompheng committed Aug 5, 2022
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  9. Make SAGE use Vélu's formulas rather than Kohel formulas 

    Initialisation of isogenies in SAGE is much faster when using
points as arguments rather than polynomials.

On SIKE_challenge this is a 10%-15% speedup.
    @remyoudompheng
    remyoudompheng committed Aug 5, 2022
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