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https://github.com/urbit/shrub.git
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272 lines
9.8 KiB
C
272 lines
9.8 KiB
C
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/* include/cash.h
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**
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** This file is in the public domain.
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*/
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/** Hash-table design:
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***
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*** The cash system is a 16-way hash tree designed to
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*** scale smoothly, remaining small for small usage
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*** and fast for big usage. It is also salted for use
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*** of multiple associations in the same table.
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***
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*** A logical key is the combination of an opaque
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*** function salt, any number < (1 << 31), and a
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*** sample list. Matches are in every case within
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*** the salt.
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***
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*** All the nouns in the sample list are equal, but
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*** duplicate. Comparing duplicates is expensive, so
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*** the hash-table stores every duplicate it finds.
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***
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*** The search key is the mug of the salt, XORed
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*** with the mug of the sample. [XX - This sacrifices
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*** efficiency to internal convenience and should
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*** be replaced with direct salt.]
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***
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*** A single slot stores a single entry. If a new entry
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*** is added, the slot expands to a 16-way table. If the
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*** table is lightly filled, slots are collision-mapped.
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*** If it is heavily filled, slots are radix-mapped.
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***
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*** Full key collisions, which are inevitable and not at
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*** all improbable, revert to linear search. 16 collisions
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*** on the same 31-bit key will produce storage failure.
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***
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*** Future revisions should add a reclamation mode based on
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*** the "clock algorithm" (a variant on LRU). The clock
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*** rotates around search-key space. Entries are reclaimed
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*** if they are clocked out and either key or value has a
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*** reference count of 1.
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**/
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/** Tunable constants.
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**/
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/* A 16-way subtable with remaining keyspace switches up to laminar
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** mode when it exceeds `cash_hi` recursively counted entries, and
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** reverts to collision mode when it falls back below `cash_lo`.
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*/
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# define u2_tune_cash_lo 6
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# define u2_tune_cash_hi 10
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/** Data types.
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**/
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/* Slot: a discriminated union.
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*/
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# define u2_slot_is_a(lot_r) (0 == (*u2_at_ray(lot_r) >> 31))
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# define u2_slot_is_b(lot_r) (3 == (*u2_at_ray(lot_r) >> 30))
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# define u2_slot_is_c(lot_r) (2 == (*u2_at_ray(lot_r) >> 30))
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/* u2_cash_slot_a: cache slot, containing exactly one entry.
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*/
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typedef struct {
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/* sel_m: opaque, unique function identity (0 for nock)
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** sap: sample list
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** pro: product
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*/
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c3_m sel_m;
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u2_noun sap;
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u2_noun pro;
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} u2_cash_slot_a;
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typedef u2_cash_slot_a u2_cash_slot;
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# define u2_slot_a_sel(lot_r) *u2_at(lot_r, u2_cash_slot_a, sel_m)
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# define u2_slot_a_sap(lot_r) *u2_at(lot_r, u2_cash_slot_a, sap)
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# define u2_slot_a_pro(lot_r) *u2_at(lot_r, u2_cash_slot_a, pro)
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# define u2_slot_gunk_coll (7 << 29)
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# define u2_slot_gunk_radx (6 << 29)
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# define u2_slot_gunk_is_coll(gun_w) (!!((gun_w) & (1 << 29)))
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# define u2_slot_gunk_is_radx(gun_w) (!((gun_w) & (1 << 29)))
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/* u2_cash_slot_b: cache slot, with 16-way table - if not empty.
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*/
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typedef struct {
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/* gun_w: gunk word - (1 << 31) at present
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** rag_w: recursive entry count
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** sid_r: ray to 16-way slot array, or 0 if rag_w is 0
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*/
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c3_w gun_w;
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c3_w rag_w;
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u2_ray sid_r;
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} u2_cash_slot_b;
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# define u2_slot_b_gun(lot_r) *u2_at(lot_r, u2_cash_slot_b, gun_w)
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# define u2_slot_b_rag(lot_r) *u2_at(lot_r, u2_cash_slot_b, rag_w)
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# define u2_slot_b_sid(lot_r) *u2_at(lot_r, u2_cash_slot_b, sid_r)
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# define u2_slot_b_sid_i(lot_r, i_w) \
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(u2_slot_b_sid(lot_r) + ((i_w) * c3_wiseof(u2_cash_slot_a)))
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/* u2_cash_slot_c: cache slot, empty
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*/
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typedef struct {
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/* emt_w: (1 << 31)
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*/
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c3_w emt_w;
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c3_w xxx_w; // unused
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c3_w xxy_w; // unused
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} u2_cash_slot_c;
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# define u2_slot_emty (1 << 31)
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# define u2_slot_c_emt(lot_r) *u2_at(lot_r, u2_cash_slot_c, emt_w)
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/** Functions.
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**/
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/* u2_cs_free():
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**
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** Release an old hashtable.
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*/
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void
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u2_cs_free(u2_ray ral_r,
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u2_ray lot_r); // submit
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/* u2_cs_mark():
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**
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** Mark traverse of slot. Return allocated words.
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*/
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c3_w
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u2_cs_mark(u2_ray ral_r,
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u2_ray lot_r);
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/* u2_cs_init():
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**
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** Initialize slot to empty.
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*/
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void
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u2_cs_init(u2_ray lot_r);
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/* u2_cs_lose():
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**
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** Release all resources in and under slot (but not slot itself).
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*/
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void
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u2_cs_lose(u2_ray ral_r,
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u2_ray lot_r); // submit
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/* u2_cs_make():
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**
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** Create a new hashtable.
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*/
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u2_ray // produce
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u2_cs_make(u2_ray ral_r);
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/* u2_cs_find():
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**
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** Find `sam` for `sel`, or return `u2_none`.
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*/
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u2_weak // discover
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u2_cs_find(u2_ray ral_r,
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u2_ray lot_r,
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c3_m sel_m,
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u2_noun sam); // retain
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/* u2_cs_find_cell():
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**
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** Find `[a b]` for `sel`, or return `u2_none`.
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*/
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u2_weak // retain
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u2_cs_find_cell(u2_ray ral_r,
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u2_ray lot_r,
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c3_m sel_m,
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u2_noun a, // retain
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u2_noun b); // retain
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/* u2_cs_find_mixt():
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**
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** Find `[a b]` for `sel`, or return `u2_none`.
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*/
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u2_weak // retain
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u2_cs_find_mixt(u2_ray ral_r,
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u2_ray lot_r,
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c3_m sel_m,
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const c3_c* a_c, // retain
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u2_noun b); // retain
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/* u2_cs_find_trel():
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**
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** Find `[a b c]` for `sel`, or return `u2_none`.
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*/
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u2_weak // retain
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u2_cs_find_trel(u2_ray ral_r,
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u2_ray lot_r,
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c3_m sel_m,
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u2_noun a, // retain
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u2_noun b, // retain
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u2_noun c); // retain
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/* u2_cs_find_qual():
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**
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** Find `[a b c d]` for `sel`, or return `u2_none`.
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*/
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u2_weak // retain
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u2_cs_find_qual(u2_ray ral_r,
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u2_ray lot_r,
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c3_m sel_m,
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u2_noun a, // retain
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u2_noun b, // retain
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u2_noun c, // retain
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u2_noun d); // retain
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/* u2_cs_save():
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**
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** Save `sam` as `pro` for `sel`. Replace existing `pro`, if any.
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*/
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u2_noun // produce
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u2_cs_save(u2_ray ral_r,
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u2_ray lot_r,
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c3_m sel_m,
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u2_noun sam, // retain
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u2_noun pro); // submit
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/* u2_cs_save_cell():
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**
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** Save `[a b]` as `pro` for `sel`.
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*/
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u2_noun // transfer
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u2_cs_save_cell(u2_ray ral_r,
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u2_ray lot_r,
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c3_m sel_m,
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u2_noun a, // retain
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u2_noun b, // retain
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u2_noun pro); // transfer
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/* u2_cs_save_mixt():
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**
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** Save `[a b]` as `pro` for `sel`.
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*/
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u2_noun // transfer
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u2_cs_save_mixt(u2_ray ral_r,
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u2_ray lot_r,
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c3_m sel_m,
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const c3_c* a_c, // retain
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u2_noun b, // retain
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u2_noun pro); // transfer
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/* u2_cs_save_trel():
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**
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** Save `[a b c]` as `pro` for `sel`.
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*/
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u2_noun // transfer
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u2_cs_save_trel(u2_ray ral_r,
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u2_ray lot_r,
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c3_m sel_m,
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u2_noun a, // retain
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u2_noun b, // retain
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u2_noun c, // retain
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u2_noun pro); // transfer
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/* u2_cs_save_qual():
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**
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** Save `[a b c d]` as `pro` for `sel`.
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*/
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u2_noun // transfer
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u2_cs_save_qual(u2_ray ral_r,
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u2_ray lot_r,
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c3_m sel_m,
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u2_noun a, // retain
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u2_noun b, // retain
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u2_noun c, // retain
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u2_noun d, // retain
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u2_noun pro); // transfer
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