kc3-lang/libxkbcommon/src/compose/table.h

Branch : - branch - android master - tag -

• Show log

  Commit

• Author : Ran Benita
  Date : 2021-03-29 16:05:14
  Hash : 02b9cabf
  Message : compose: use a ternary tree instead of a regular trie Previously we used a simple trie with a linked list for each chain. Unfortunately most compose files have very long chains which means the constructions performs an almost quadratic number of comparisons. Switch to using a ternary search tree instead. This is very similar to a trie, only the linked list is essentially replaced with a binary tree. On the en_US/Compose file, the perf diff is the following (the modified function is `parse`): Event 'cycles:u' Baseline Delta Abs Shared Object Symbol ........ ......... ................ ................................. 39.91% -17.62% bench-compose [.] parse.constprop.0 20.54% +6.47% bench-compose [.] lex 17.28% +5.55% libc-2.33.so [.] __strcmp_avx2 12.78% +4.01% bench-compose [.] xkb_keysym_from_name 2.30% +0.83% libc-2.33.so [.] __GI_____strtoull_l_internal 3.36% +0.78% bench-compose [.] strcmp@plt Thanks to some careful packing, the memory usage is pretty much the same. Signed-off-by: Ran Benita <ran@unusedvar.com>

• src/compose/table.h

• /*
   * Copyright © 2013,2021 Ran Benita <ran234@gmail.com>
   *
   * Permission is hereby granted, free of charge, to any person obtaining a
   * copy of this software and associated documentation files (the "Software"),
   * to deal in the Software without restriction, including without limitation
   * the rights to use, copy, modify, merge, publish, distribute, sublicense,
   * and/or sell copies of the Software, and to permit persons to whom the
   * Software is furnished to do so, subject to the following conditions:
   *
   * The above copyright notice and this permission notice (including the next
   * paragraph) shall be included in all copies or substantial portions of the
   * Software.
   *
   * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
   * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
   * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
   * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
   * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
   * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
   * DEALINGS IN THE SOFTWARE.
   */
  
  #ifndef COMPOSE_COMPOSE_H
  #define COMPOSE_COMPOSE_H
  
  #include "xkbcommon/xkbcommon-compose.h"
  #include "utils.h"
  #include "context.h"
  
  /*
   * The compose table data structure is a ternary search tree.
   *
   * Reference: https://www.drdobbs.com/database/ternary-search-trees/184410528
   * Visualization: https://www.cs.usfca.edu/~galles/visualization/TST.html
   *
   * Short example. Given these sequences:
   *
   *      <B> <C>        : "first"  dead_a
   *      <B> <D> <E>    : "second" dead_b
   *      <A> <F>        : "third"  dead_c
   *
   * the tree would look like:
   *
   *          -------- [<B>]---------
   *          |          |          #
   *          v          V
   *     -- [<A>] --   [<C>] --------
   *     #    |    #     |          |
   *          v          #     -- [<D>] --
   *     -- [<F>] --           #    |    #
   *     #    |    #                v
   *          #                -- [<E>] --
   *                           #    |    #
   *                                #
   *
   * where:
   * - [<X>] is a node for a sequence keysym <X>.
   * - right arrows are `hikid` pointers.
   * - left arrows are `lokid` pointers.
   * - down arrows are `eqkid` pointers.
   * - # is a nil pointer.
   *
   * The nodes are all kept in a contiguous array.  Pointers are represented
   * as integer offsets into this array.  A nil pointer is represented as 0
   * (which, helpfully, is the offset of an empty dummy node).
   *
   * Nodes without an eqkid are leaf nodes.  Since a sequence cannot be a
   * prefix of another, these are exactly the nodes which terminate the
   * sequences (in a bijective manner).
   *
   * A leaf contains the result data of its sequence.  The result keysym is
   * contained in the node struct itself; the result UTF-8 string is a byte
   * offset into an array of the form "\0first\0second\0third" (the initial
   * \0 is so offset 0 points to an empty string).
   */
  
  /* Fits in uint16_t, also a good idea to have some limit. */
  #define MAX_COMPOSE_NODES 65535
  
  struct compose_node {
      xkb_keysym_t keysym;
  
      /* Offset into xkb_compose_table::nodes or 0. */
      uint16_t lokid;
      /* Offset into xkb_compose_table::nodes or 0. */
      uint16_t hikid;
  
      union {
          struct {
              uint32_t _pad:31;
              bool is_leaf:1;
          };
          struct {
              uint32_t _pad:31;
              bool is_leaf:1;
              /* Offset into xkb_compose_table::nodes or 0. */
              uint16_t eqkid;
          } internal;
          struct {
              /* Offset into xkb_compose_table::utf8. */
              uint32_t utf8:31;
              bool is_leaf:1;
              xkb_keysym_t keysym;
          } leaf;
      };
  };
  
  struct xkb_compose_table {
      int refcnt;
      enum xkb_compose_format format;
      enum xkb_compose_compile_flags flags;
      struct xkb_context *ctx;
  
      char *locale;
  
      darray_char utf8;
      darray(struct compose_node) nodes;
  };
  
  #endif