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+/*
+ Copyright 2011-2014 David Robillard <http://drobilla.net>
+
+ Permission to use, copy, modify, and/or distribute this software for any
+ purpose with or without fee is hereby granted, provided that the above
+ copyright notice and this permission notice appear in all copies.
+
+ THIS SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+
+#include <assert.h>
+#include <stdbool.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "symap.h"
+
+/**
+ @file symap.c Implementation of Symap, a basic symbol map (string interner).
+
+ This implementation is primitive, but has some desirable qualities: good
+ (O(lg(n)) lookup performance for already-mapped symbols, minimal space
+ overhead, extremely fast (O(1)) reverse mapping (ID to string), simple code,
+ no dependencies.
+
+ The tradeoff is that mapping new symbols may be quite slow. In other words,
+ this implementation is ideal for use cases with a relatively limited set of
+ symbols, or where most symbols are mapped early. It will not fare so well
+ with very dynamic sets of symbols. For that, you're better off with a
+ tree-based implementation (and the associated space cost, especially if you
+ need reverse mapping).
+*/
+
+struct SymapImpl {
+ /**
+ Unsorted array of strings, such that the symbol for ID i is found
+ at symbols[i - 1].
+ */
+ char** symbols;
+
+ /**
+ Array of IDs, sorted by corresponding string in `symbols`.
+ */
+ uint32_t* index;
+
+ /**
+ Number of symbols (number of items in `symbols` and `index`).
+ */
+ uint32_t size;
+};
+
+Symap*
+symap_new(void)
+{
+ Symap* map = (Symap*)malloc(sizeof(Symap));
+ map->symbols = NULL;
+ map->index = NULL;
+ map->size = 0;
+ return map;
+}
+
+void
+symap_free(Symap* map)
+{
+ for (uint32_t i = 0; i < map->size; ++i) {
+ free(map->symbols[i]);
+ }
+
+ free(map->symbols);
+ free(map->index);
+ free(map);
+}
+
+static char*
+symap_strdup(const char* str)
+{
+ const size_t len = strlen(str);
+ char* copy = (char*)malloc(len + 1);
+ memcpy(copy, str, len + 1);
+ return copy;
+}
+
+/**
+ Return the index into map->index (not the ID) corresponding to `sym`,
+ or the index where a new entry for `sym` should be inserted.
+*/
+static uint32_t
+symap_search(const Symap* map, const char* sym, bool* exact)
+{
+ *exact = false;
+ if (map->size == 0) {
+ return 0; // Empty map, insert at 0
+ } else if (strcmp(map->symbols[map->index[map->size - 1] - 1], sym) < 0) {
+ return map->size; // Greater than last element, append
+ }
+
+ uint32_t lower = 0;
+ uint32_t upper = map->size - 1;
+ uint32_t i = upper;
+ int cmp;
+
+ while (upper >= lower) {
+ i = lower + ((upper - lower) / 2);
+ cmp = strcmp(map->symbols[map->index[i] - 1], sym);
+
+ if (cmp == 0) {
+ *exact = true;
+ return i;
+ } else if (cmp > 0) {
+ if (i == 0) {
+ break; // Avoid underflow
+ }
+ upper = i - 1;
+ } else {
+ lower = ++i;
+ }
+ }
+
+ assert(!*exact || strcmp(map->symbols[map->index[i] - 1], sym) > 0);
+ return i;
+}
+
+uint32_t
+symap_try_map(Symap* map, const char* sym)
+{
+ bool exact;
+ const uint32_t index = symap_search(map, sym, &exact);
+ if (exact) {
+ assert(!strcmp(map->symbols[map->index[index]], sym));
+ return map->index[index];
+ }
+
+ return 0;
+}
+
+uint32_t
+symap_map(Symap* map, const char* sym)
+{
+ bool exact;
+ const uint32_t index = symap_search(map, sym, &exact);
+ if (exact) {
+ assert(!strcmp(map->symbols[map->index[index] - 1], sym));
+ return map->index[index];
+ }
+
+ const uint32_t id = ++map->size;
+ char* const str = symap_strdup(sym);
+
+ /* Append new symbol to symbols array */
+ map->symbols = (char**)realloc(map->symbols, map->size * sizeof(str));
+ map->symbols[id - 1] = str;
+
+ /* Insert new index element into sorted index */
+ map->index = (uint32_t*)realloc(map->index, map->size * sizeof(uint32_t));
+ if (index < map->size - 1) {
+ memmove(map->index + index + 1,
+ map->index + index,
+ (map->size - index - 1) * sizeof(uint32_t));
+ }
+
+ map->index[index] = id;
+
+ return id;
+}
+
+const char*
+symap_unmap(Symap* map, uint32_t id)
+{
+ if (id == 0) {
+ return NULL;
+ } else if (id <= map->size) {
+ return map->symbols[id - 1];
+ }
+ return NULL;
+}
+
+#ifdef STANDALONE
+
+#include <stdio.h>
+
+static void
+symap_dump(Symap* map)
+{
+ fprintf(stderr, "{\n");
+ for (uint32_t i = 0; i < map->size; ++i) {
+ fprintf(stderr, "\t%u = %s\n",
+ map->index[i], map->symbols[map->index[i] - 1]);
+ }
+ fprintf(stderr, "}\n");
+}
+
+int
+main()
+{
+ #define N_SYMS 5
+ char* syms[N_SYMS] = {
+ "hello", "bonjour", "goodbye", "aloha", "salut"
+ };
+
+ Symap* map = symap_new();
+ for (int i = 0; i < N_SYMS; ++i) {
+ if (symap_try_map(map, syms[i])) {
+ fprintf(stderr, "error: Symbol already mapped\n");
+ return 1;
+ }
+
+ const uint32_t id = symap_map(map, syms[i]);
+ if (strcmp(map->symbols[id - 1], syms[i])) {
+ fprintf(stderr, "error: Corrupt symbol table\n");
+ return 1;
+ }
+
+ if (symap_map(map, syms[i]) != id) {
+ fprintf(stderr, "error: Remapped symbol to a different ID\n");
+ return 1;
+ }
+
+ symap_dump(map);
+ }
+
+ symap_free(map);
+ return 0;
+}
+
+#endif /* STANDALONE */