75   // return NULL.
  76   HeapWord* allocate(size_t word_sz) {
  77     HeapWord* res = _top;
  78     if (pointer_delta(_end, _top) >= word_sz) {
  79       _top = _top + word_sz;
  80       return res;
  81     } else {
  82       return NULL;
  83     }
  84   }
  85 
  86   // Undo the last allocation in the buffer, which is required to be of the
  87   // "obj" of the given "word_sz".
  88   void undo_allocation(HeapWord* obj, size_t word_sz) {
  89     assert(pointer_delta(_top, _bottom) >= word_sz, "Bad undo");
  90     assert(pointer_delta(_top, obj)     == word_sz, "Bad undo");
  91     _top = obj;
  92   }
  93 
  94   // The total (word) size of the buffer, including both allocated and
  95   // unallocted space.
  96   size_t word_sz() { return _word_sz; }
  97 
  98   // Should only be done if we are about to reset with a new buffer of the
  99   // given size.
 100   void set_word_size(size_t new_word_sz) {
 101     assert(new_word_sz > AlignmentReserve, "Too small");
 102     _word_sz = new_word_sz;
 103   }
 104 
 105   // The number of words of unallocated space remaining in the buffer.
 106   size_t words_remaining() {
 107     assert(_end >= _top, "Negative buffer");
 108     return pointer_delta(_end, _top, HeapWordSize);
 109   }
 110 
 111   bool contains(void* addr) {
 112     return (void*)_bottom <= addr && addr < (void*)_hard_end;
 113   }
 114 
 115   // Sets the space of the buffer to be [buf, space+word_sz()).

  75   // return NULL.
  76   HeapWord* allocate(size_t word_sz) {
  77     HeapWord* res = _top;
  78     if (pointer_delta(_end, _top) >= word_sz) {
  79       _top = _top + word_sz;
  80       return res;
  81     } else {
  82       return NULL;
  83     }
  84   }
  85 
  86   // Undo the last allocation in the buffer, which is required to be of the
  87   // "obj" of the given "word_sz".
  88   void undo_allocation(HeapWord* obj, size_t word_sz) {
  89     assert(pointer_delta(_top, _bottom) >= word_sz, "Bad undo");
  90     assert(pointer_delta(_top, obj)     == word_sz, "Bad undo");
  91     _top = obj;
  92   }
  93 
  94   // The total (word) size of the buffer, including both allocated and
  95   // unallocated space.
  96   size_t word_sz() { return _word_sz; }
  97 
  98   // Should only be done if we are about to reset with a new buffer of the
  99   // given size.
 100   void set_word_size(size_t new_word_sz) {
 101     assert(new_word_sz > AlignmentReserve, "Too small");
 102     _word_sz = new_word_sz;
 103   }
 104 
 105   // The number of words of unallocated space remaining in the buffer.
 106   size_t words_remaining() {
 107     assert(_end >= _top, "Negative buffer");
 108     return pointer_delta(_end, _top, HeapWordSize);
 109   }
 110 
 111   bool contains(void* addr) {
 112     return (void*)_bottom <= addr && addr < (void*)_hard_end;
 113   }
 114 
 115   // Sets the space of the buffer to be [buf, space+word_sz()).