The previous portability fix bounded the powi test's drift from std::powi
at an absolute ULP count, but Windows/MSVC drift grows with the exponent
(3 ULP by exp=14), so no fixed ULP bound is portable.
Replace the ULP oracle with a loose relative-tolerance sanity sweep
(1e-11), which any sane libm clears by ~1000x regardless of exponent
while still catching a grossly wrong impl. Add a golden-bit pin for the
exp=14 case that exposed the growth. The powi function is unchanged; the
golden-bit determinism pins already passed on Windows.
The powi guard test asserted our square-and-multiply result was
bit-for-bit equal to f64::powi, which failed the Windows unit-test job by
one ULP. f64::powi is not portably bit-stable: Linux and macOS lower it
to compiler-rt's __powidf2, but Windows/MSVC rounds differently.
Our square-and-multiply is pure IEEE-754 f64 multiplication and is
therefore deterministic across every platform, which is the property that
actually matters for mesh nodes to agree on bloom FPR and backoff timing
regardless of OS. Replace the std bit-equality assertion with golden-bit
pins on our own output (locking that cross-platform determinism) plus a
bounded-drift sanity sweep against std::powi. The powi function itself is
unchanged.
Bring the proto tree closer to a std+alloc-only posture, behavior unchanged on
every decision path:
- Sweep the remaining std::fmt and std::collections imports over to core::fmt
and alloc::collections across the wire codecs and their tests. Subsystem files
that shadow the core name with a child core module use the leading-colon
::core::fmt form. Imports only.
- Replace the two f64::powi calls (bloom false-positive-rate, FMP backoff timer)
with a shared core-only square-and-multiply helper in proto/math, bit-identical
to std::powi (a guard test pins this against every exponent the codecs reach),
and route the diagnostic estimated-count natural log through libm::log. The FPR
reject decision and the backoff timer are bit-for-bit unchanged; only the
debug-only count estimate may differ by at most one ULP.
Johnathan Corgan