451       rest = rest >> 1;
 452     }
 453   }
 454   return true;
 455 }
 456 
 457 BitMap::idx_t* BitMap::_pop_count_table = NULL;
 458 
 459 void BitMap::init_pop_count_table() {
 460   if (_pop_count_table == NULL) {
 461     BitMap::idx_t *table = NEW_C_HEAP_ARRAY(idx_t, 256, mtInternal);
 462     for (uint i = 0; i < 256; i++) {
 463       table[i] = num_set_bits(i);
 464     }
 465 
 466     intptr_t res = Atomic::cmpxchg_ptr((intptr_t)  table,
 467                                        (intptr_t*) &_pop_count_table,
 468                                        (intptr_t)  NULL_WORD);
 469     if (res != NULL_WORD) {
 470       guarantee( _pop_count_table == (void*) res, "invariant" );
 471       FREE_C_HEAP_ARRAY(idx_t, table, mtInternal);
 472     }
 473   }
 474 }
 475 
 476 BitMap::idx_t BitMap::num_set_bits(bm_word_t w) {
 477   idx_t bits = 0;
 478 
 479   while (w != 0) {
 480     while ((w & 1) == 0) {
 481       w >>= 1;
 482     }
 483     bits++;
 484     w >>= 1;
 485   }
 486   return bits;
 487 }
 488 
 489 BitMap::idx_t BitMap::num_set_bits_from_table(unsigned char c) {
 490   assert(_pop_count_table != NULL, "precondition");
 491   return _pop_count_table[c];

 451       rest = rest >> 1;
 452     }
 453   }
 454   return true;
 455 }
 456 
 457 BitMap::idx_t* BitMap::_pop_count_table = NULL;
 458 
 459 void BitMap::init_pop_count_table() {
 460   if (_pop_count_table == NULL) {
 461     BitMap::idx_t *table = NEW_C_HEAP_ARRAY(idx_t, 256, mtInternal);
 462     for (uint i = 0; i < 256; i++) {
 463       table[i] = num_set_bits(i);
 464     }
 465 
 466     intptr_t res = Atomic::cmpxchg_ptr((intptr_t)  table,
 467                                        (intptr_t*) &_pop_count_table,
 468                                        (intptr_t)  NULL_WORD);
 469     if (res != NULL_WORD) {
 470       guarantee( _pop_count_table == (void*) res, "invariant" );
 471       FREE_C_HEAP_ARRAY(idx_t, table);
 472     }
 473   }
 474 }
 475 
 476 BitMap::idx_t BitMap::num_set_bits(bm_word_t w) {
 477   idx_t bits = 0;
 478 
 479   while (w != 0) {
 480     while ((w & 1) == 0) {
 481       w >>= 1;
 482     }
 483     bits++;
 484     w >>= 1;
 485   }
 486   return bits;
 487 }
 488 
 489 BitMap::idx_t BitMap::num_set_bits_from_table(unsigned char c) {
 490   assert(_pop_count_table != NULL, "precondition");
 491   return _pop_count_table[c];