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/* Implement a cached obstack.

   Written by Fred Fish <fnf@cygnus.com>

   Rewritten by Jim Blandy <jimb@cygnus.com>

   Copyright 1999 Free Software Foundation, Inc.

   This file is part of GDB.

   This program is free software; you can redistribute it and/or modify

   it under the terms of the GNU General Public License as published by

   the Free Software Foundation; either version 2 of the License, or

   (at your option) any later version.

   This program is distributed in the hope that it will be useful,

   but WITHOUT ANY WARRANTY; without even the implied warranty of

   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License

   along with this program; if not, write to the Free Software

   Foundation, Inc., 59 Temple Place - Suite 330,

   Boston, MA 02111-1307, USA.  */

#include <stddef.h>

#include <stdlib.h>

#include "defs.h"

#include "obstack.h"

#include "bcache.h"

#include "gdb_string.h"         /* For memcpy declaration */

/* The hash function.  */

unsigned long

hash (void *addr, int length)

{

  /* If it's a short string, hash on every character.  Otherwise, sample

     characters from throughout the string.  */

  if (length <= 64)

    {

      char *byte = addr;

      unsigned long h = 0;

      int i;

      for (i = 0; i < length; i++)

        h = h * 65793 ^ (h >> (sizeof (h) * 8 - 6)) ^ byte[i];

      return h;

    }

  else

    {

      char *byte = addr;

      int n, i;

      unsigned long h = 0;

      for (n = i = 0; n < 64; n++)

        {

          h = h * 65793 + (h >> (sizeof (h) * 8 - 6)) + byte[i];

          i = h % length;

        }

      return h;

    }

}

/* Growing the bcache's hash table.  */

/* If the average chain length grows beyond this, then we want to

   resize our hash table.  */

#define CHAIN_LENGTH_THRESHOLD (5)

static void

expand_hash_table (struct bcache *bcache)

{

  /* A table of good hash table sizes.  Whenever we grow, we pick the

     next larger size from this table.  sizes[i] is close to 1 << (i+10),

     so we roughly double the table size each time.  After we fall off

     the end of this table, we just double.  Don't laugh --- there have

     been executables sighted with a gigabyte of debug info.  */

  static unsigned long sizes[] = {

    1021, 2053, 4099, 8191, 16381, 32771,

    65537, 131071, 262144, 524287, 1048573, 2097143,

    4194301, 8388617, 16777213, 33554467, 67108859, 134217757,

    268435459, 536870923, 1073741827, 2147483659UL

  };

  unsigned int new_num_buckets;

  struct bstring **new_buckets;

  unsigned int i;

  /* Find the next size.  */

  new_num_buckets = bcache->num_buckets * 2;

  for (i = 0; i < (sizeof (sizes) / sizeof (sizes[0])); i++)

    if (sizes[i] > bcache->num_buckets)

      {

        new_num_buckets = sizes[i];

        break;

      }

  /* Allocate the new table.  */

  {

    size_t new_size = new_num_buckets * sizeof (new_buckets[0]);

    new_buckets = (struct bstring **) xmalloc (new_size);

    memset (new_buckets, 0, new_size);

    bcache->structure_size -= (bcache->num_buckets

                               * sizeof (bcache->bucket[0]));

    bcache->structure_size += new_size;

  }

  /* Rehash all existing strings.  */

  for (i = 0; i < bcache->num_buckets; i++)

    {

      struct bstring *s, *next;

      for (s = bcache->bucket[i]; s; s = next)

        {

          struct bstring **new_bucket;

          next = s->next;

          new_bucket = &new_buckets[(hash (&s->d.data, s->length)

                                     % new_num_buckets)];

          s->next = *new_bucket;

          *new_bucket = s;

        }

    }

  /* Plug in the new table.  */

  if (bcache->bucket)

    free (bcache->bucket);

  bcache->bucket = new_buckets;

  bcache->num_buckets = new_num_buckets;

}

/* Looking up things in the bcache.  */

/* The number of bytes needed to allocate a struct bstring whose data

   is N bytes long.  */

#define BSTRING_SIZE(n) (offsetof (struct bstring, d.data) + (n))

/* Find a copy of the LENGTH bytes at ADDR in BCACHE.  If BCACHE has

   never seen those bytes before, add a copy of them to BCACHE.  In

   either case, return a pointer to BCACHE's copy of that string.  */

void *

bcache (void *addr, int length, struct bcache *bcache)

{

  int hash_index;

  struct bstring *s;

  /* If our average chain length is too high, expand the hash table.  */

  if (bcache->unique_count >= bcache->num_buckets * CHAIN_LENGTH_THRESHOLD)

    expand_hash_table (bcache);

  bcache->total_count++;

  bcache->total_size += length;

  hash_index = hash (addr, length) % bcache->num_buckets;

  /* Search the hash bucket for a string identical to the caller's.  */

  for (s = bcache->bucket[hash_index]; s; s = s->next)

    if (s->length == length

        && ! memcmp (&s->d.data, addr, length))

      return &s->d.data;

  /* The user's string isn't in the list.  Insert it after *ps.  */

  {

    struct bstring *new

      = obstack_alloc (&bcache->cache, BSTRING_SIZE (length));

    memcpy (&new->d.data, addr, length);

    new->length = length;

    new->next = bcache->bucket[hash_index];

    bcache->bucket[hash_index] = new;

    bcache->unique_count++;

    bcache->unique_size += length;

    bcache->structure_size += BSTRING_SIZE (length);

    return &new->d.data;

  }

}

/* Freeing bcaches.  */

/* Free all the storage associated with BCACHE.  */

void

free_bcache (struct bcache *bcache)

{

  obstack_free (&bcache->cache, 0);

  if (bcache->bucket)

    free (bcache->bucket);

  /* This isn't necessary, but at least the bcache is always in a

     consistent state.  */

  memset (bcache, 0, sizeof (*bcache));

}

/* Printing statistics.  */

static int

compare_ints (const void *ap, const void *bp)

{

  /* Because we know we're comparing two ints which are positive,

     there's no danger of overflow here.  */

  return * (int *) ap - * (int *) bp;

}

static void

print_percentage (int portion, int total)

{

  if (total == 0)

    printf_filtered ("(not applicable)\n");

  else

    printf_filtered ("%3d%%\n", portion * 100 / total);

}

/* Print statistics on BCACHE's memory usage and efficacity at

   eliminating duplication.  NAME should describe the kind of data

   BCACHE holds.  Statistics are printed using `printf_filtered' and

   its ilk.  */

void

print_bcache_statistics (struct bcache *c, char *type)

{

  int occupied_buckets;

  int max_chain_length;

  int median_chain_length;

  /* Count the number of occupied buckets, and measure chain lengths.  */

  {

    unsigned int b;

    int *chain_length

      = (int *) alloca (c->num_buckets * sizeof (*chain_length));

    occupied_buckets = 0;

    for (b = 0; b < c->num_buckets; b++)

      {

        struct bstring *s = c->bucket[b];

        chain_length[b] = 0;

        if (s)

          {

            occupied_buckets++;

            while (s)

              {

                chain_length[b]++;

                s = s->next;

              }

          }

      }

    /* To compute the median, we need the set of chain lengths sorted.  */

    qsort (chain_length, c->num_buckets, sizeof (chain_length[0]),

           compare_ints);

    if (c->num_buckets > 0)

      {

        max_chain_length = chain_length[c->num_buckets - 1];

        median_chain_length = chain_length[c->num_buckets / 2];

      }

    else

      {

        max_chain_length = 0;

        median_chain_length = 0;

      }

  }

  printf_filtered ("  Cached '%s' statistics:\n", type);

  printf_filtered ("    Total object count:  %ld\n", c->total_count);

  printf_filtered ("    Unique object count: %lu\n", c->unique_count);

  printf_filtered ("    Percentage of duplicates, by count: ");

  print_percentage (c->total_count - c->unique_count, c->total_count);

  printf_filtered ("\n");

  printf_filtered ("    Total object size:   %ld\n", c->total_size);

  printf_filtered ("    Unique object size:  %ld\n", c->unique_size);

  printf_filtered ("    Percentage of duplicates, by size:  ");

  print_percentage (c->total_size - c->unique_size, c->total_size);

  printf_filtered ("\n");

  printf_filtered ("    Total memory used by bcache, including overhead: %ld\n",

                   c->structure_size);

  printf_filtered ("    Percentage memory overhead: ");

  print_percentage (c->structure_size - c->unique_size, c->unique_size);

  printf_filtered ("    Net memory savings:         ");

  print_percentage (c->total_size - c->structure_size, c->total_size);

  printf_filtered ("\n");

  printf_filtered ("    Hash table size:           %3d\n", c->num_buckets);

  printf_filtered ("    Hash table population:     ");

  print_percentage (occupied_buckets, c->num_buckets);

  printf_filtered ("    Median hash chain length:  %3d\n",

                   median_chain_length);

  printf_filtered ("    Average hash chain length: ");

  if (c->num_buckets > 0)

    printf_filtered ("%3lu\n", c->unique_count / c->num_buckets);

  else

    printf_filtered ("(not applicable)\n");

  printf_filtered ("    Maximum hash chain length: %3d\n", max_chain_length);

  printf_filtered ("\n");

}