Opened 15 months ago

Closed 13 months ago

#31676 closed defect (fixed)

Hash of mpmath complex numbers produces OverFlowError

Reported by: soehms Owned by:
Priority: major Milestone: sage-9.4
Component: python3 Keywords: mpmath complex hash
Cc: malb, vdelecroix Merged in:
Authors: Sebastian Oehms Reviewers: Dima Pasechnik, Travis Scrimshaw
Report Upstream: N/A Work issues:
Branch: 3e82038 (Commits, GitHub, GitLab) Commit: 3e8203807cfee4f0951820b1f6bfc82a0561d33e
Dependencies: Stopgaps:

Status badges

Description

The issue is decribed by the following example: 

sage: from mpmath import mpc
sage: hash(mpc(1, -1))
---------------------------------------------------------------------------
OverflowError                             Traceback (most recent call last)
<ipython-input-2-ff647837f542> in <module>
----> 1 hash(mpc(Integer(1), -Integer(1)))

~/devel/sage/local/lib/python3.9/site-packages/sage/libs/mpmath/ext_main.pyx in sage.libs.mpmath.ext_main.mpc.__hash__ (build/cythonized/sage/libs/mpmath/ext_main.c:27881)()
   2496             True
   2497         """
-> 2498         return libmp.mpc_hash(self._mpc_)
   2499
   2500     def __neg__(s):

OverflowError: Python int too large to convert to C ssize_t

Change History (7)

comment:1 Changed 15 months ago by soehms

  • Branch set to u/soehms/mpmath_hash

comment:2 Changed 15 months ago by soehms

  • Commit set to 3e8203807cfee4f0951820b1f6bfc82a0561d33e
  • Status changed from new to needs_review

Its seems that __hash__ cannot return a Python3 int which is not an int in Python2. Therefore, my solution is to take the hash of the result of libmp.mpc_hash.

New commits:

​3e8203831676: initial version

comment:3 Changed 15 months ago by dimpase

  • Reviewers set to Dima Pasechnik

comment:4 Changed 15 months ago by dimpase

  • Cc malb vdelecroix added

Can someone who knows something about hash functions comment on the quality of the resulting hash function? We don't want too many collisions....

comment:5 Changed 15 months ago by tscrim

  • Reviewers changed from Dima Pasechnik to Dima Pasechnik, Travis Scrimshaw
  • Status changed from needs_review to positive_review

All it is doing is using Python's hashing of a long int into a ssize_t sized int, which has to be a good hash function (at least, I highly doubt we could do better than the Python developers for this).

comment:6 Changed 15 months ago by soehms

Thanks!

comment:7 Changed 13 months ago by vbraun

  • Branch changed from u/soehms/mpmath_hash to 3e8203807cfee4f0951820b1f6bfc82a0561d33e
  • Resolution set to fixed
  • Status changed from positive_review to closed
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