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