Changeset 40094f in git for factory/cf_util.cc

Timestamp:

Jul 2, 2020, 10:22:19 AM (4 years ago)

Author:

Hans Schoenemann <hannes@…>

Branches:

(u'spielwiese', 'fe61d9c35bf7c61f2b6cbf1b56e25e2f08d536cc')

Children:

53acc46a104d727e78284f0fda06b0ac9460dfae

Parents:

45e2d2305421369847cac77695d8c7aedcbfa7e5

Message:

move SI_LOG2 to factory/si_log2.h

File:

• factory/cf_util.cc (modified) (1 diff)

factory/cf_util.cc

@@ -39 +39 @@
 }
 
-int ilog2 (int a)
+int ilog2 (int v)
 {
-  int n = -1;
-  while ( a > 0 )
-  {
-    n++;
-    a /=2;
-  }
-  return n;
+  const unsigned int b[] = {0x2, 0xC, 0xF0, 0xFF00, 0xFFFF0000};
+  const unsigned int S[] = {1, 2, 4, 8, 16};
+
+  unsigned int r = 0; // result of log2(v) will go here
+  if (v & b[4]) { v >>= S[4]; r |= S[4]; }
+  if (v & b[3]) { v >>= S[3]; r |= S[3]; }
+  if (v & b[2]) { v >>= S[2]; r |= S[2]; }
+  if (v & b[1]) { v >>= S[1]; r |= S[1]; }
+  if (v & b[0]) { v >>= S[0]; r |= S[0]; }
+  return (int)r;
 }