src/hotspot/share/utilities/bitMap.cpp

rev 52445 : 8211926: Catastrophic size_t underflow in BitMap::*_large methods
Reviewed-by: kbarrett

*** 261,278 ****
      clear_range_within_word(beg, boundary);
      clear_range_within_word(boundary, end);
    }
  }
  
  void BitMap::set_large_range(idx_t beg, idx_t end) {
    verify_range(beg, end);
  
    idx_t beg_full_word = word_index_round_up(beg);
    idx_t end_full_word = word_index(end);
  
!   assert(end_full_word - beg_full_word >= 32,
!          "the range must include at least 32 bytes");
  
    // The range includes at least one full word.
    set_range_within_word(beg, bit_index(beg_full_word));
    set_large_range_of_words(beg_full_word, end_full_word);
    set_range_within_word(bit_index(end_full_word), end);
--- 261,288 ----
      clear_range_within_word(beg, boundary);
      clear_range_within_word(boundary, end);
    }
  }
  
+ bool BitMap::is_small_range_of_words(idx_t beg_full_word, idx_t end_full_word) {
+   // There is little point to call large version on small ranges.
+   // Need to check carefully, keeping potential idx_t underflow in mind.
+   // The threshold should be at least one word.
+   STATIC_ASSERT(small_range_words >= 1);
+   return (beg_full_word + small_range_words >= end_full_word);
+ }
+ 
  void BitMap::set_large_range(idx_t beg, idx_t end) {
    verify_range(beg, end);
  
    idx_t beg_full_word = word_index_round_up(beg);
    idx_t end_full_word = word_index(end);
  
!   if (is_small_range_of_words(beg_full_word, end_full_word)) {
!     set_range(beg, end);
!     return;
!   }
  
    // The range includes at least one full word.
    set_range_within_word(beg, bit_index(beg_full_word));
    set_large_range_of_words(beg_full_word, end_full_word);
    set_range_within_word(bit_index(end_full_word), end);
*** 282,292 ****
    verify_range(beg, end);
  
    idx_t beg_full_word = word_index_round_up(beg);
    idx_t end_full_word = word_index(end);
  
!   if (end_full_word - beg_full_word < 32) {
      clear_range(beg, end);
      return;
    }
  
    // The range includes at least one full word.
--- 292,302 ----
    verify_range(beg, end);
  
    idx_t beg_full_word = word_index_round_up(beg);
    idx_t end_full_word = word_index(end);
  
!   if (is_small_range_of_words(beg_full_word, end_full_word)) {
      clear_range(beg, end);
      return;
    }
  
    // The range includes at least one full word.
*** 366,377 ****
    verify_range(beg, end);
  
    idx_t beg_full_word = word_index_round_up(beg);
    idx_t end_full_word = word_index(end);
  
!   assert(end_full_word - beg_full_word >= 32,
!          "the range must include at least 32 bytes");
  
    // The range includes at least one full word.
    par_put_range_within_word(beg, bit_index(beg_full_word), value);
    if (value) {
      set_large_range_of_words(beg_full_word, end_full_word);
--- 376,389 ----
    verify_range(beg, end);
  
    idx_t beg_full_word = word_index_round_up(beg);
    idx_t end_full_word = word_index(end);
  
!   if (is_small_range_of_words(beg_full_word, end_full_word)) {
!     par_at_put_range(beg, end, value);
!     return;
!   }
  
    // The range includes at least one full word.
    par_put_range_within_word(beg, bit_index(beg_full_word), value);
    if (value) {
      set_large_range_of_words(beg_full_word, end_full_word);