+ * Copied and slightly adapted from the linux source tree, version 4.9.39
+ * (2017-07).
+ */
+__a_const static uint32_t fls64(uint64_t v)
+{
+ int n = 63;
+ const uint64_t ones = ~(uint64_t)0U;
+
+ if ((v & (ones << 32)) == 0) {
+ n -= 32;
+ v <<= 32;
+ }
+ if ((v & (ones << (64 - 16))) == 0) {
+ n -= 16;
+ v <<= 16;
+ }
+ if ((v & (ones << (64 - 8))) == 0) {
+ n -= 8;
+ v <<= 8;
+ }
+ if ((v & (ones << (64 - 4))) == 0) {
+ n -= 4;
+ v <<= 4;
+ }
+ if ((v & (ones << (64 - 2))) == 0) {
+ n -= 2;
+ v <<= 2;
+ }
+ if ((v & (ones << (64 - 1))) == 0)
+ n -= 1;
+ return n;
+}
+
+/*
+ * Compute the integer square root floor(sqrt(x)).