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Add utility ldexp and frexp functions to prevent dealing with the shift of
ldshiftexp and frshiftexp everywhere.
Also move primitive integer tests to place all primitive tests in the
same directory.
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All the implementations now return (0, 0) when the dividend is so large
that the quotient would overflow.
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There are three implementations of this primitive:
* one in OCaml on 63 bits integer in kernel/uint63_amd64.ml
* one in OCaml on Int64 in kernel/uint63_x86.ml
* one in C on unsigned 64 bit integers in kernel/byterun/coq_uint63_native.h
Its specification is the axiom `diveucl_21_spec` in
theories/Numbers/Cyclic/Int63/Int63.v
* comment the implementations with loop invariants to enable an easy
pen&paper proof of correctness (note to reviewers: the one in
uint63_amd64.ml might be the easiest to read)
* make sure the three implementations are equivalent
* fix the specification in Int63.v
(only the lowest part of the result is actually returned)
* make a little optimisation in div21 enabled by the proof of correctness
(cmp is computed at the end of the first loop rather than at the beginning,
potentially saving one loop iteration while remaining correct)
* update the proofs in Int63.v and Cyclic63.v to take into account the
new specifiation of div21
* add a test
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This work makes it possible to take advantage of a compact
representation for integers in the entire system, as opposed to only
in some reduction machines. It is useful for heavily computational
applications, where even constructing terms is not possible without such
a representation.
Concretely, it replaces part of the retroknowledge machinery with
a primitive construction for integers in terms, and introduces a kind of
FFI which maps constants to operators (on integers). Properties of these
operators are expressed as explicit axioms, whereas they were hidden in
the retroknowledge-based approach.
This has been presented at the Coq workshop and some Coq Working Groups,
and has been used by various groups for STM trace checking,
computational analysis, etc.
Contributions by Guillaume Bertholon and Pierre Roux <Pierre.Roux@onera.fr>
Co-authored-by: Benjamin Grégoire <Benjamin.Gregoire@inria.fr>
Co-authored-by: Vincent Laporte <Vincent.Laporte@fondation-inria.fr>
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