stillwater-sc / universal / 26338255293

84%

master: 84%

Build Type

push

github

Committed by web-flow

Commit Message

fix(ereal): improve regression tests for ereal (#943)

* fix(ereal): improve regression tests

* fix(ereal): canonicalise expansion after operator+= / operator-=

The new addition tests in this PR (commutativity, associativity)
exposed a real implementation bug, not a test issue. The MSVC failure
the user observed reproduces on Linux gcc and clang too.

Root cause
- `linear_expansion_sum` (Shewchuk Figure 7) produces a non-overlapping
  expansion but not a canonical Priest-form one. The same real value
  emerges as different limb sequences depending on input ordering:

    (a + b) + c with a=1e+15, b=1, c=1e-15 -> [1e+15, 1e-15]      (2 limbs)
    (c + b) + a with same values            -> [1e+15, 1.11e-15, -1.10e-16]
                                                                 (3 limbs)

  Both represent the same real value. `compare_adaptive` does a
  limb-by-limb walk, so it (correctly) reports the two representations
  as unequal -- breaking the commutativity / associativity / equality
  contracts the new tests assert.

Fix
- Pipe the linear_expansion_sum result through renormalize_expansion
  (already in expansion_ops.hpp; uses grow_expansion to rebuild as a
  canonical non-overlapping expansion that's representation-unique).
- Applied to operator+=(ereal), operator+=(double), operator-=(ereal).
  operator-=(double) delegates to operator-=(ereal) so inherits the fix.
- Multiplication/division have separate code paths and are not touched.

Cost: one O(m) renormalize pass per add/sub. Acceptable given that
without it the type does not satisfy basic algebraic invariants.

Validation
- gcc 13.3 debug + release: PR's new addition tests PASS; full ereal
  regression (38 tests) PASS.
- clang 18.1 debug + release: same.
- The MSVC commutativity failure the user reported should also clear
  once CI reruns -- the bug was platform-independent, just unmasked
  by the new commutativity test.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic... (continued)

Coverage Stats

3 of 3 new or added lines in 1 file covered. (100.0%)

13 existing lines in 4 files now uncovered.

47120 of 55911 relevant lines covered (84.28%)

5265880.75 hits per line