@@ -381,18 +381,23 @@ static inline uint64_t pow2floor(uint64_t value)
return 0x8000000000000000ull >> clz64(value);
}
-/* round up to the nearest power of 2 (0 if overflow) */
+/*
+ * Return @value rounded up to the nearest power of two modulo 2^64.
+ * This is *zero* for @value > 2^63, so be careful.
+ */
static inline uint64_t pow2ceil(uint64_t value)
{
- uint8_t nlz = clz64(value);
-
- if (is_power_of_2(value)) {
- return value;
- }
- if (!nlz) {
- return 0;
+ int n = clz64(value - 1);
+
+ if (!n) {
+ /*
+ * @value - 1 has no leading zeroes, thus @value - 1 >= 2^63
+ * Therefore, either @value == 0 or @value > 2^63.
+ * If it's 0, return 1, else return 0.
+ */
+ return !value;
}
- return 1ULL << (64 - nlz);
+ return 0x8000000000000000ull >> (n - 1);
}
/**