X-Git-Url: http://git.tuebingen.mpg.de/?p=paraslash.git;a=blobdiff_plain;f=mood.c;fp=mood.c;h=c24b3d8b9da25c011e237b40e4508b0b61894598;hp=54d7b85fa411ef65031d716b6a6d8bb7818b9720;hb=e79198e9851faddfd64e47654b5bc66fbc574255;hpb=ae183bb0cf15903c4d6bf72d0c814ced9f1b261d

diff --git a/mood.c b/mood.c
index 54d7b85f..c24b3d8b 100644
--- a/mood.c
+++ b/mood.c
@@ -84,6 +84,42 @@ struct mood {
  */
 static struct mood *current_mood;
 
+/*
+ * Find the position of the most-significant set bit.
+ *
+ * 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;
+}
+
 /*
  * Rough approximation to sqrt.
  *
@@ -96,10 +132,7 @@ __a_const static uint64_t int_sqrt(uint64_t x)
 	op = x;
 	res = 0;
 
-	one = one << 62;
-	while (one > op)
-		one >>= 2;
-
+	one = one << (fls64(x) & ~one);
 	while (one != 0) {
 		if (op >= res + one) {
 			op = op - (res + one);