jets: +grab jet for the +sip lazy jam cursor - #1054
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Jets the hot path of +sip (urbit/urbit#7385): +grab, atom at axis in a jammed noun. Registered as an i-tier library jet under %non/%sip, mirroring lagoon/math. The jet subsumes +dive, +gaze, +fetch, and the +hop skips on the path -- one jet, one parity surface. pkg/noun/jets/i/sip.c: no C recursion (explicit pending-node skip counter), 64-bit bit-cursor arithmetic, bounds-checked against u3r_met. Malformed input, overrun, forward/self backref, out-of-range axis, and type mismatch all u3m_bail(c3__exit) exactly where the Hoon crashes -- crash parity. Registration in 135/tree.c (%non/sip/grab), decls in w.h/q.h, source wired into build.zig. Verified: jet binds and every +grab result matches +cue / +slot ground truth across the +sip parity suite; head-tag dispatch on a 1 MB jam is ~880x faster than +cue, flat across 1 KB -> 10 MB payloads. Companion to urbit/urbit#7385 (the +sip library and tests). Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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Jul 5, 2026
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Draft — companion to urbit/urbit#7385 (the
+siplibrary and tests). Merge that first; this is the jet for its hot path.Summary
+sipis a read-only cursor over a jammed noun (see urbit/urbit#7385). This jets its one hot entry point —+grab, atom at axis — as ani-tier library jet under%non/%sip, mirroringlagoon/math. The jet subsumes+dive,+gaze,+fetch, and the+hopskips on the path: one jet, one parity surface.pkg/noun/jets/i/sip.c—u3wi_sip_grab(wrapper) /u3qi_sip_grab(core). No C recursion — the subtree skip uses an explicit pending-node counter (O(1) space). 64-bit (c3_d) bit-cursor arithmetic; every read bounds-checked againstu3r_met(0, a).pkg/noun/jets/135/tree.c— register%non/sip/grab(k135; the running kernel is~% %k.135).pkg/noun/jets/w.h,q.h— declareu3wi_sip_grab/u3qi_sip_grab.pkg/noun/build.zig— wire injets/i/sip.c.Crash parity
Malformed input, buffer overrun, a forward or self backref, an out-of-range axis, axis-into-atom, and fetch-of-cell all
u3m_bail(c3__exit)— exactly where the Hoon spec crashes. Following a backref asserts a strictly-decreasing offset, so hostile backref chains terminate by construction.Verification
Built (
DEVELOPER_DIR=/nonexistent zig build -Dtarget=aarch64-macos) and booted on a fake ship with the+siplibrary from urbit/urbit#7385:+grabresult matched+cue/+slotground truth over the full suite — hand-computed USTJ vectors, 400 random DAG-shaped nouns (forced cell + atom backrefs), and hostile-input crash tests. Full%/teststree green.+grabon a[%tag …]head-tag lookup is flat at 1.27 µs across 1 KB → 10 MB jams (<1% spread) and ~880× faster than+cue+slot at 1 MB (~9000× at 10 MB); ~16× over the same walk un-jetted. Worst case (5000-deep right-spine, deepest axis, O(N)): jetted+grab303 µs vs 71 ms un-jetted (235×) and still beats cue+slot for a single lookup. Full table in lib: add +sip lazy jam cursor urbit#7385.No changes to
jam/cue/mat/rub; this is purely additive.🤖 Generated with Claude Code