Mysql源码学习——没那么简单的Hash(4)

{

  DBUG_ENTER("my_hash_init");

  DBUG_PRINT("enter",("hash: 0x%lx  size: %u", (long) hash, (uint) size));

  hash->records=0;

  hash->key_offset=key_offset;

  hash->key_length=key_length;

  hash->blength=1;

  hash->get_key=get_key;

  hash->free=free_element;

  hash->flags=flags;

  hash->charset=charset;

  DBUG_RETURN(my_init_dynamic_array_ci(&hash->array,

                                       sizeof(HASH_LINK), size, growth_size));

}

<font size="3">   可以看到，_my_hash_init函数主要是初始化HASH结构体和hash->array（DYNAMIC_ARRAY结构体）。</font>

动态HASH函数

<font size="3">   我们首先来看下hash函数的定义：</font>

static inline char*

my_hash_key(const HASH *hash, const uchar *record, size_t *length,

            my_bool first)

{

  if (hash->get_key)

    return (char*) (*hash->get_key)(record,length,first);

  *length=hash->key_length;

  return (char*) record+hash->key_offset;

}

static uint my_hash_mask(my_hash_value_type hashnr, size_t buffmax,

                         size_t maxlength)

{

  if ((hashnr & (buffmax-1)) < maxlength) return (hashnr & (buffmax-1));

  return (hashnr & ((buffmax >> 1) -1));

}