libgo/runtime/go-map-index.c

   1 /* go-map-index.c -- find or insert an entry in a map.
   2
   3    Copyright 2009 The Go Authors. All rights reserved.
   4    Use of this source code is governed by a BSD-style
   5    license that can be found in the LICENSE file.  */
   6
   7 #include <stddef.h>
   8 #include <stdlib.h>
   9
  10 #include "runtime.h"
  11 #include "go-alloc.h"
  12 #include "go-assert.h"
  13 #include "map.h"
  14
  15 /* Rehash MAP to a larger size.  */
  16
  17 static void
  18 __go_map_rehash (struct __go_map *map)
  19 {
  20   const struct __go_map_descriptor *descriptor;
  21   const struct __go_type_descriptor *key_descriptor;
  22   uintptr_t key_offset;
  23   size_t key_size;
  24   uintptr_t (*hashfn) (const void *, uintptr_t);
  25   uintptr_t old_bucket_count;
  26   void **old_buckets;
  27   uintptr_t new_bucket_count;
  28   void **new_buckets;
  29   uintptr_t i;
  30
  31   descriptor = map->__descriptor;
  32
  33   key_descriptor = descriptor->__map_descriptor->__key_type;
  34   key_offset = descriptor->__key_offset;
  35   key_size = key_descriptor->__size;
  36   hashfn = key_descriptor->__hashfn;
  37
  38   old_bucket_count = map->__bucket_count;
  39   old_buckets = map->__buckets;
  40
  41   new_bucket_count = __go_map_next_prime (old_bucket_count * 2);
  42   new_buckets = (void **) __go_alloc (new_bucket_count * sizeof (void *));
  43   __builtin_memset (new_buckets, 0, new_bucket_count * sizeof (void *));
  44
  45   for (i = 0; i < old_bucket_count; ++i)
  46     {
  47       char* entry;
  48       char* next;
  49
  50       for (entry = old_buckets[i]; entry != NULL; entry = next)
  51         {
  52           size_t key_hash;
  53           size_t new_bucket_index;
  54
  55           /* We could speed up rehashing at the cost of memory space
  56              by caching the hash code.  */
  57           key_hash = hashfn (entry + key_offset, key_size);
  58           new_bucket_index = key_hash % new_bucket_count;
  59
  60           next = *(char **) entry;
  61           *(char **) entry = new_buckets[new_bucket_index];
  62           new_buckets[new_bucket_index] = entry;
  63         }
  64     }
  65
  66   __go_free (old_buckets);
  67
  68   map->__bucket_count = new_bucket_count;
  69   map->__buckets = new_buckets;
  70 }
  71
  72 /* Find KEY in MAP, return a pointer to the value.  If KEY is not
  73    present, then if INSERT is false, return NULL, and if INSERT is
  74    true, insert a new value and zero-initialize it before returning a
  75    pointer to it.  */
  76
  77 void *
  78 __go_map_index (struct __go_map *map, const void *key, _Bool insert)
  79 {
  80   const struct __go_map_descriptor *descriptor;
  81   const struct __go_type_descriptor *key_descriptor;
  82   uintptr_t key_offset;
  83   _Bool (*equalfn) (const void*, const void*, uintptr_t);
  84   size_t key_hash;
  85   size_t key_size;
  86   size_t bucket_index;
  87   char *entry;
  88
  89   if (map == NULL)
  90     {
  91       if (insert)
  92         runtime_panicstring ("assignment to entry in nil map");
  93       return NULL;
  94     }
  95
  96   descriptor = map->__descriptor;
  97
  98   key_descriptor = descriptor->__map_descriptor->__key_type;
  99   key_offset = descriptor->__key_offset;
 100   key_size = key_descriptor->__size;
 101   __go_assert (key_size != -1UL);
 102   equalfn = key_descriptor->__equalfn;
 103
 104   key_hash = key_descriptor->__hashfn (key, key_size);
 105   bucket_index = key_hash % map->__bucket_count;
 106
 107   entry = (char *) map->__buckets[bucket_index];
 108   while (entry != NULL)
 109     {
 110       if (equalfn (key, entry + key_offset, key_size))
 111         return entry + descriptor->__val_offset;
 112       entry = *(char **) entry;
 113     }
 114
 115   if (!insert)
 116     return NULL;
 117
 118   if (map->__element_count >= map->__bucket_count)
 119     {
 120       __go_map_rehash (map);
 121       bucket_index = key_hash % map->__bucket_count;
 122     }
 123
 124   entry = (char *) __go_alloc (descriptor->__entry_size);
 125   __builtin_memset (entry, 0, descriptor->__entry_size);
 126
 127   __builtin_memcpy (entry + key_offset, key, key_size);
 128
 129   *(char **) entry = map->__buckets[bucket_index];
 130   map->__buckets[bucket_index] = entry;
 131
 132   map->__element_count += 1;
 133
 134   return entry + descriptor->__val_offset;
 135 }