static struct mood *current_mood;
/*
- * Rough approximation to sqrt.
+ * Find the position of the most-significant set bit.
*
- * It returns an integer res with res * res <= x. Taken 2007 from the linux
- * source tree.
+ * Copied and slightly adapted from the linux source tree, version 4.9.39
+ * (2017-07).
*/
-__a_const static uint64_t int_sqrt(uint64_t x)
+__a_const static uint32_t fls64(uint64_t v)
{
- uint64_t op, res, one = 1;
- op = x;
- res = 0;
+ int n = 63;
+ const uint64_t ones = ~(uint64_t)0U;
- one = one << 62;
- while (one > op)
- one >>= 2;
+ 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)).
+ *
+ * Taken 2007 from the linux source tree.
+ */
+__a_const static uint64_t int_sqrt(uint64_t x)
+{
+ uint64_t op = x, res = 0, one = 1;
+ one = one << (fls64(x) & ~one);
while (one != 0) {
if (op >= res + one) {
op = op - (res + one);
- res = res + 2 * one;
+ res = res + 2 * one;
}
res /= 2;
one /= 4;
}
-// PARA_NOTICE_LOG("sqrt(%llu) = %llu\n", x, res);
return res;
}