Add a more complete example of use.

example/ex-mph.c

@@ -0,0 +1,236 @@
+#include <stdio.h>
+#include <stdint.h>
+
+#include "m-array.h"
+#include "m-dict.h"
+#include "m-string.h"
+#include "m-algo.h"
+
+/* Based on:
+ *  Easy Perfect Minimal Hashing 
+ *  By Steve Hanov. Released to the public domain.
+ *  http://stevehanov.ca/blog/index.php?id=119
+ *
+ * Based on:
+ * Edward A. Fox, Lenwood S. Heath, Qi Fan Chen and Amjad M. Daoud, 
+ * "Practical minimal perfect hash functions for large databases", CACM, 35(1):105-121
+ *
+ * also a good reference:
+ *  Compress, Hash, and Displace algorithm by Djamal Belazzougui,
+ * Fabiano C. Botelho, and Martin Dietzfelbinger
+ */
+
+
+
+/* Define the needed data structure : */
+
+// Define a dictionnary of constant string --> integer
+DICT_DEF2(dict_mph, const char *, M_CSTR_OPLIST, uint32_t, M_DEFAULT_OPLIST)
+#define M_OPL_dict_mph_t() DICT_OPLIST(dict_mph, M_CSTR_OPLIST, M_DEFAULT_OPLIST)
+
+// Defin an array of integer
+ARRAY_DEF(array_value, uint32_t) // Start from 1. 0 is 'None'
+#define M_OPL_array_value_t() ARRAY_OPLIST(array_value)
+
+// Defin an array of integer
+ARRAY_DEF(array_seed, int32_t)
+#define M_OPL_array_seed_t() ARRAY_OPLIST(array_seed)
+ALGO_DEF(array_seed, M_OPL_array_seed_t())
+
+// Define an array of constant string that are ordered by their size.
+ARRAY_DEF(array_cstr, const char *, M_CSTR_OPLIST)
+static inline int array_cstr_cmp(const array_cstr_t a, const array_cstr_t b) {
+  size_t sa = array_cstr_size(a);
+  size_t sb = array_cstr_size(b);
+  return (sa > sb) ? -1 : (sa < sb);
+}
+#define M_OPL_array_cstr_t() M_OPEXTEND(ARRAY_OPLIST(array_cstr, M_CSTR_OPLIST), CMP(array_cstr_cmp))
+
+// Define an array of array of constant string, and some algo over this container
+ARRAY_DEF(array_bucket, array_cstr_t)
+#define M_OPL_array_bucket_t() ARRAY_OPLIST(array_bucket, M_OPL_array_cstr_t() )
+ALGO_DEF(array_bucket, M_OPL_array_bucket_t())
+
+// Define an array of string to save the input.
+ARRAY_DEF(array_string, string_t)
+#define M_OPL_array_string_t() ARRAY_OPLIST(array_string, M_OPL_string_t())
+
+
+
+
+// The algorithm may not converge on all inputs.
+// Example: dictionnary with only 'a' and 'e'
+// The hash function doesn't provide the needed property.
+static uint32_t hash(int32_t seed, const char str[])
+{
+  if (seed == 0) seed = 0x01000193;
+  while (*str) {
+    seed = ((seed * 0x01000193) ^ *str);
+    str++;
+  }
+  return seed;
+}
+
+
+
+// Step 1: place all key keys into buckets
+static void
+CreateMinimalPerfectHash1(array_seed_t seed, array_value_t value,
+                          array_bucket_t bucket,
+                          const dict_mph_t dict)
+{
+  size_t size = dict_mph_size (dict);
+  
+  array_value_resize(value, size);
+  array_seed_resize(seed, size);
+  array_bucket_resize(bucket, size);
+
+  for M_EACH(item, dict, dict_mph_t) {
+      size_t i = hash(0, item->key) % size;
+      array_cstr_push_back (*array_bucket_get (bucket, i), item->key);
+    }
+}
+
+// Step 2:   Sort the buckets and process the ones with the most items first.
+static void
+CreateMinimalPerfectHash2(array_seed_t seed, array_value_t value,
+                          array_bucket_t bucket,
+                          const dict_mph_t dict)
+{
+  size_t size = dict_mph_size (dict);
+  array_bucket_sort(bucket);
+  M_LET(slots, array_seed_t) {
+    for M_EACH(b, bucket, array_bucket_t) {
+        if (array_cstr_size(*b) <= 1)
+          break;
+        size_t d = 1;
+        /* Repeatedly try different values of d until we find a hash function
+           that places all items in the bucket into free slots.
+           This may loop forever on some inputs if the hash function is not good
+           enought. */
+        for(bool cont = true; cont ; ) {
+          cont = false;
+          array_seed_clean(slots);
+          for M_EACH(it, *b, array_cstr_t) {
+              size_t s = hash(d, *it) % size;
+              if (*array_value_get(value, s) != 0 || array_seed_contains(slots, s)){
+                d++;
+                cont = true;
+                break;
+              }
+              array_seed_push_back (slots, s);
+            }
+        }
+        // Fill in the seed & value with the computed value
+        array_seed_set_at(seed, hash(0, *array_cstr_get(*b, 0)) % size, d);
+        d = 0;
+        for M_EACH(it, *b, array_cstr_t) {
+            array_value_set_at(value,
+                               *array_seed_get(slots, d),
+                               *dict_mph_get(dict, *it));
+            d++;
+          }
+      }
+  }
+}
+
+/* Step 3: 
+ * Only buckets with 1 item remain. Process them more quickly by directly
+ * placing them into a free slot. Use a negative value of d to indicate
+ * this.
+ */
+static void
+CreateMinimalPerfectHash3(array_seed_t seed, array_value_t value,
+                          array_bucket_t bucket,
+                          const dict_mph_t dict)
+{
+  size_t size = dict_mph_size (dict);
+
+  M_LET(freelist, array_seed_t) {
+    // Get a list of available slot
+    for(size_t i = 0; i < size; i++)
+      if (*array_value_get(value, i) == 0)
+        array_seed_push_back(freelist, i);
+    for M_EACH(b, bucket, array_bucket_t) {
+        if (array_cstr_size(*b) != 1)
+          continue;
+        int32_t slot;
+        array_seed_pop_back(&slot, freelist);
+        /*We subtract one to ensure it's negative even if the zeroeth slot was
+          used. */
+        array_seed_set_at (seed, hash(0, *array_cstr_get(*b, 0)) % size,
+                           -slot-1);
+        array_value_set_at(value, slot, *dict_mph_get(dict, *array_cstr_get(*b, 0)));
+      }
+  }
+}
+
+static void
+CreateMinimalPerfectHash(array_seed_t seed, array_value_t value,
+                         const dict_mph_t dict)
+{
+  M_LET(bucket, array_bucket_t) {
+    CreateMinimalPerfectHash1(seed, value, bucket, dict);
+    CreateMinimalPerfectHash2(seed, value, bucket, dict);
+    CreateMinimalPerfectHash3(seed, value, bucket, dict);
+  }
+}
+
+static void
+dict_read_from_file(dict_mph_t dict, array_string_t arr, const char filename[])
+{
+  FILE *f = fopen(filename, "rt");
+  if (!f) abort();
+  uint32_t line = 1;
+  M_LET(str, string_t) {
+    while (!feof(f) && !ferror(f)) {
+      string_fgets(str, f, STRING_READ_PURE_LINE);
+      string_strim(str);
+      if (!string_empty_p(str)) {
+        // Not clean as items of 'dict' points are linked to items of 'arr'
+        array_string_push_back (arr, str);
+        dict_mph_set_at(dict, string_get_cstr(*array_string_back(arr)), line);
+        line++;
+      }
+    }
+  }
+  fclose(f);
+}
+
+static uint32_t
+perfect_hash_lockup(array_seed_t seed, array_value_t value,
+                    const char key[])
+{
+  int32_t s = *array_seed_get(seed, hash(0, key) % array_seed_size(seed));
+  if (s < 0)
+    return *array_value_get(value, -s-1);
+  else
+    return *array_value_get(value, hash(s, key) % array_value_size(value));
+}
+
+static void
+test(array_seed_t seed, array_value_t value, dict_mph_t dict)
+{
+  for M_EACH(item, dict, dict_mph_t) {
+      const char *key = item->key;
+      uint32_t v = perfect_hash_lockup(seed, value, key);
+      if (v != item->value) {
+        fprintf(stderr, "ERROR for %s: %u VS %u\n", key, v, item->value);
+      }
+    }
+}
+
+int main(int argc, const char *argv[])
+{
+  M_LET(arr, array_string_t)
+    M_LET(dict, dict_mph_t)
+    M_LET(seed, array_seed_t)
+    M_LET(value, array_value_t) {
+    const char *filename = (argc > 1) ? argv[1] :"/usr/share/dict/words";
+    dict_read_from_file(dict, arr, filename);
+    CreateMinimalPerfectHash(seed, value, dict);
+    test(seed, value, dict);
+  }
+  
+  return 0;
+}