2014-09-10 20:06:30 +04:00
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/* include/n/hash.h
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2014-09-06 00:13:24 +04:00
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**
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** This file is in the public domain.
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*/
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/** Straightforward implementation of the classic Bagwell
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*** HAMT (hash array mapped trie), using a mug hash.
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***
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*** Because a mug is 31 bits, the root table is 64 wide.
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*** Thereupon 5 bits each are warm for each layer. The
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*** final leaf is simply a linear search.
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***
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*** We store an extra "freshly warm" bit for a simple
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*** clock-algorithm reclamation policy, not yet implemented.
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*** Search "clock algorithm" to figure it out.
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**/
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/* u3_ch_slot: map slot.
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**
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** Either a key-value cell or a loom offset, decoded as a pointer
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** to a u3_ch_node. Matches the u3_noun format - coordinate with
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** meme.h. The top two bits are:
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**
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** 00 - empty (in the root table only)
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** 01 - table
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** 02 - entry, stale
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** 03 - entry, fresh
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*/
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typedef c3_w u3_ch_slot;
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/* u3_ch_node: map node.
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*/
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typedef struct {
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c3_w map_w;
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u3_ch_slot sot_w[0];
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} u3_ch_node;
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/* u3_ch_root: hash root table, with future-proof clock.
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*/
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typedef struct {
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c3_w clk_w;
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u3_ch_slot sot_w[64];
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} u3_ch_root;
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/* u3_ch_buck: bottom bucket.
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*/
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typedef struct {
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c3_w len_w;
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u3_noun kev[0];
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} u3_ch_buck;
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/** HAMT macros.
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***
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*** Coordinate with u3_noun definition!
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**/
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/* u3_ch_slot_is_null(): yes iff slot is empty
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** u3_ch_slot_is_noun(): yes iff slot contains a key/value cell
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** u3_ch_slot_is_node(): yes iff slot contains a subtable/bucket
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** u3_ch_slot_is_warm(): yes iff fresh bit is set
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** u3_ch_slot_to_node(): slot to node pointer
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** u3_ch_node_to_slot(): node pointer to slot
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** u3_ch_slot_to_noun(): slot to cell
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** u3_ch_noun_to_slot(): cell to slot
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*/
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# define u3_ch_slot_is_null(sot) ((0 == ((sot) >> 30)) ? u3_yes : u3_no)
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# define u3_ch_slot_is_node(sot) ((1 == ((sot) >> 30)) ? u3_yes : u3_no)
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# define u3_ch_slot_is_noun(sot) ((1 == ((sot) >> 31)) ? u3_yes : u3_no)
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# define u3_ch_slot_is_warm(sot) (((sot) & 0x40000000) ? u3_yes : u3_no)
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# define u3_ch_slot_to_node(sot) (u3_co_into((sot) & 0x3fffffff))
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# define u3_ch_node_to_slot(ptr) (u3_co_outa(ptr) | 0x40000000)
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# define u3_ch_slot_to_noun(sot) (0x40000000 | (sot))
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# define u3_ch_noun_to_slot(som) (som)
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# define u3_ch_noun_be_warm(sot) ((sot) | 0x40000000)
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# define u3_ch_noun_be_cold(sot) ((sot) & ~0x40000000)
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