X-Git-Url: http://git.tuebingen.mpg.de/?p=paraslash.git;a=blobdiff_plain;f=mood.c;h=c06f695c36f8d29664cc48e2e877a7d758702913;hp=584c46b8fa375f24d2f87492d44f67ac902fa98b;hb=177ea8ea46918a925c0d2d8a07e7fbe9f478a40c;hpb=3d3a2f50a05501cf27f1155629799953f952bd4b

diff --git a/mood.c b/mood.c
index 584c46b8..c06f695c 100644
--- a/mood.c
+++ b/mood.c
@@ -93,32 +93,60 @@ struct mood {
  */
 static struct mood *current_mood;
 
-/**
- * Rough approximation to sqrt.
+/*
+ * Find the position of the most-significant set bit.
  *
- * \param x Integer of which to calculate the sqrt.
+ * 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)).
  *
- * \return An integer res with res * res <= x.
+ * Taken 2007 from the linux source tree.
  */
 __a_const static uint64_t int_sqrt(uint64_t x)
 {
-	uint64_t op, res, one = 1;
-	op = x;
-	res = 0;
-
-	one = one << 62;
-	while (one > op)
-		one >>= 2;
+	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;
 }