ppkarwasz commented on code in PR #1379:
URL: https://github.com/apache/commons-lang/pull/1379#discussion_r2086790446
##########
src/main/java/org/apache/commons/lang3/CachedRandomBits.java:
##########
@@ -52,6 +52,16 @@ final class CachedRandomBits {
*/
private int bitIndex;
+ /**
+ * The maximum size of the cache.
+ *
+ * <p>
+ * This is dictated by the {@code if (bitIndex >> 3 >= cache.length)} in
the {@link #nextBits(int)} method.
+ * Essentially {@code 63_913_202 << 3 } will overflow so this line will
never evaluate to true.
+ * At some point the {@code bitIndex += generatedBitsInIteration} will
overflow and cause an exception.
+ */
+ private static final int MAX_CACHE_SIZE = 63_913_200;
Review Comment:
The value here should rather be `0x1FFF_FFFF` (i.e. `268_435_455`, but in
hex it is easier to understand).
`63_913_201` is the highest `x` such that `(21x + 3) / 5 + 10 ≤ 268 435 455`.
##########
src/main/java/org/apache/commons/lang3/RandomStringUtils.java:
##########
@@ -330,8 +329,8 @@ public static String random(int count, int start, int end,
final boolean letters
// Ideally the cache size depends on multiple factor, including the
cost of generating x bytes
// of randomness as well as the probability of rejection. It is
however not easy to know
// those values programmatically for the general case.
- // To prevent overflow restrict the cache size to 60M entries (
- final int cacheSize = Math.min ((count * gapBits + 3) / 5 + 10,
MAX_CACHE_SIZE);
+ // For huge strings the padding required can cause an overflow
+ final int cacheSize = (count * gapBits + 3) / 5 + 10 > 0 ? (count *
gapBits + 3) / 5 + 10 : Integer.MAX_VALUE;
Review Comment:
```suggestion
final int cacheSize = count * gapBits + 3 > 0 ? (count * gapBits +
3) / 5 + 10 : Integer.MAX_VALUE;
```
Adding `10` can transform a negative number into a small positive one.
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