vpx_mem/memory_manager/hmm_shrink.c

   1 /*
   2  *  Copyright (c) 2010 The WebM project authors. All Rights Reserved.
   3  *
   4  *  Use of this source code is governed by a BSD-style license
   5  *  that can be found in the LICENSE file in the root of the source
   6  *  tree. An additional intellectual property rights grant can be found
   7  *  in the file PATENTS.  All contributing project authors may
   8  *  be found in the AUTHORS file in the root of the source tree.
   9  */
  10
  11
  12 /* This code is in the public domain.
  13 ** Version: 1.1  Author: Walt Karas
  14 */
  15
  16 #include "hmm_intrnl.h"
  17
  18 void U(shrink_chunk)(U(descriptor) *desc, U(size_bau) n_baus_to_shrink)
  19 {
  20     head_record *dummy_end_block = (head_record *)
  21                                    BAUS_BACKWARD(desc->end_of_shrinkable_chunk, DUMMY_END_BLOCK_BAUS);
  22
  23 #ifdef HMM_AUDIT_FAIL
  24
  25     if (dummy_end_block->block_size != 0)
  26         /* Chunk does not have valid dummy end block. */
  27         HMM_AUDIT_FAIL
  28
  29 #endif
  30
  31         if (n_baus_to_shrink)
  32         {
  33             head_record *last_block = (head_record *)
  34                                       BAUS_BACKWARD(
  35                                           dummy_end_block, dummy_end_block->previous_block_size);
  36
  37 #ifdef HMM_AUDIT_FAIL
  38             AUDIT_BLOCK(last_block)
  39 #endif
  40
  41             if (last_block == desc->last_freed)
  42             {
  43                 U(size_bau) bs = BLOCK_BAUS(last_block);
  44
  45                 /* Chunk will not be shrunk out of existence if
  46                 ** 1.  There is at least one allocated block in the chunk
  47                 **     and the amount to shrink is exactly the size of the
  48                 **     last block, OR
  49                 ** 2.  After the last block is shrunk, there will be enough
  50                 **     BAUs left in it to form a minimal size block. */
  51                 int chunk_will_survive =
  52                     (PREV_BLOCK_BAUS(last_block) && (n_baus_to_shrink == bs)) ||
  53                     (n_baus_to_shrink <= (U(size_bau))(bs - MIN_BLOCK_BAUS));
  54
  55                 if (chunk_will_survive ||
  56                     (!PREV_BLOCK_BAUS(last_block) &&
  57                      (n_baus_to_shrink ==
  58                       (U(size_bau))(bs + DUMMY_END_BLOCK_BAUS))))
  59                 {
  60                     desc->last_freed = 0;
  61
  62                     if (chunk_will_survive)
  63                     {
  64                         bs -= n_baus_to_shrink;
  65
  66                         if (bs)
  67                         {
  68                             /* The last (non-dummy) block was not completely
  69                             ** eliminated by the shrink. */
  70
  71                             last_block->block_size = bs;
  72
  73                             /* Create new dummy end record.
  74                             */
  75                             dummy_end_block =
  76                                 (head_record *) BAUS_FORWARD(last_block, bs);
  77                             dummy_end_block->previous_block_size = bs;
  78                             dummy_end_block->block_size = 0;
  79
  80 #ifdef HMM_AUDIT_FAIL
  81
  82                             if (desc->avl_tree_root)
  83                                 AUDIT_BLOCK(PTR_REC_TO_HEAD(desc->avl_tree_root))
  84 #endif
  85
  86                                 U(into_free_collection)(desc, last_block);
  87                         }
  88                         else
  89                         {
  90                             /* The last (non-dummy) block was completely
  91                             ** eliminated by the shrink.  Make its head
  92                             ** the new dummy end block.
  93                             */
  94                             last_block->block_size = 0;
  95                             last_block->previous_block_size &= ~HIGH_BIT_BAU_SIZE;
  96                         }
  97                     }
  98                 }
  99
 100 #ifdef HMM_AUDIT_FAIL
 101                 else
 102                     HMM_AUDIT_FAIL
 103 #endif
 104                 }
 105
 106 #ifdef HMM_AUDIT_FAIL
 107             else
 108                 HMM_AUDIT_FAIL
 109 #endif
 110             }
 111 }