bignum operator layer: TBigInt + - * div mod comparisons — Track B

• Type: feature (library) — Track B
• Status: done [[feature-lib-vecmath]] / [[feature-pascal-complex-numbers-ucomplex]]
• Owner: fable-p

What

lib/rtl/bignum.pas already has the machinery as functions (BigAdd, BigAddSigned, BigSub, BigMul, ... TBigInt record). Add the operator layer on top: + - * and div (tkDiv IS in the declarable set), `= <> < <= >

=via the existing signed compare.mod` needs the op-set one-liner — note on [[feature-pascal-operator-slash-overload]]. Keep the function API untouched (operators = thin wrappers).

Why

Makes bignum pleasant (c := a * b + a; on 200-digit ints) and is the third operator-overloading workout: unlike complex/vecmath these records hold heap/managed payloads (check TBigInt's rep!) — operator results as temporaries in chained expressions exercise the managed-record temp lifetime path (see project_managed_record_byval_arg_temp landmine). If TBigInt is a managed record, this test coverage is exactly where a refcount/double-free bug would surface.

Tests

lib-suite golden test: factorial(50), 2^512, +/- around sign flips, div/mod identities (a = (a div b)*b + a mod b), comparison matrix, chained expressions forcing operator temporaries. All integer-exact — no FP determinism concerns.

Gate

Track B: build with $(PXX_STABLE), make lib-test green. A managed-temp crash found here → Track A ticket with minimal repro, don't work around.

Log

• 2026-07-11 — resolved, commit 78ab71c8.