leftBitCount

1 files changed, 23 insertions, 1 deletions

diff --git a/bits.c b/bits.c
index 8297011..c5c08fa 100644
--- a/bits.c
+++ b/bits.c
@@ -155,7 +155,29 @@ int logicalShift(int x, int n) {
  *   Difficulty: 4
  */
 int leftBitCount(int x) {
-    return 2;
+    int shift = 16;
+    int t = !((((x >> shift) & 0xFFFF) ^ 0xFFFF));
+    int count = t << 4;
+
+    shift = 24 + ~count + 1;
+    t = !((((x >> shift) & 0xFF) ^ 0xFF));
+    count = count + (t << 3);
+
+    shift = 28 + ~count + 1;
+    t = !((((x >> shift) & 0xF) ^ 0xF));
+    count = count + (t << 2);
+
+    shift = 30 + ~count + 1;
+    t = !((((x >> shift) & 0x3) ^ 0x3));
+    count = count + (t << 1);
+
+    shift = 31 + ~count + 1;
+    t = !((((x >> shift) & 0x1) ^ 0x1));
+    count = count + t;
+
+    count = count + !(~x);
+
+    return count;
 }
 
 /*