rajamesandClaude Opus 5.5
9a391eb0ad
UM* as first written in DECOMPOSITION.md section 4 was exact only while u1 <= 2^(n-2): plain +* loses the carry out of T and its shift keeps T's sign bit, so the loop is exact only while S and T stay in [-2^(n-2), 2^(n-2)). The rewrite multiplies by s = u1 2/, which always lies in that range, starting T at t0 = u2 2/ when u1 is odd, so the loop yields hi:lo = t0 + s*u2 exactly. Then u1*u2 = 2*(hi:lo) + c_lo + c_hi*2^n c_lo = u1 & u2 & 1 c_hi = (u1<0 ? u2 : 0) + (u1 odd and u2<0 ? 1 : 0) restores the halved-away bits and the unsigned reading of both top bits. test_foundation.c runs the new definition against v4_umul over every pair of the edge vectors plus 20000 pseudo-random pairs, at 32- and 64-bit cells, optimised and under ASan+UBSan. The two pinned failing cases are now ordinary exactness checks. Two hand mutations of the correction step each fail more than 10000 checks at both widths. DECOMPOSITION.md: section 4 UM* replaced, D-3 ruling text updated. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
v4/
StarForth v4: the 32-instruction F18-derived core. The design lives in
docs/v4.0.0/JUSTIFICATION.md (why) and docs/v4.0.0/DECOMPOSITION.md
(every v3 word mapped to a v4 fate).
The first deliverable is the hosted C99 golden model (JUSTIFICATION.md §10,
step 1). It must pass POST and hold K≡1.0 with 32- and 64-bit cells on all
three host ISAs.
What exists so far is the single node: registers, circular stacks, memory, all
32 opcodes, and per-opcode and per-call-target heat. make -C v4 test builds
and runs the tests at both cell widths; make -C v4 sanitize repeats them
under ASan and UBSan. There is no compiler capsule, no POST and no K
measurement yet.