counting bits!

gowrikumar/src/07-countbits.c

@@ -0,0 +1,40 @@
+/**
+ * :author: Dan Buch (daniel.buch@gmail.com)
+ */
+
+#include <stdio.h>
+
+static unsigned int mask[] = {
+    0x55555555,
+    0x33333333,
+    0x0F0F0F0F,
+    0x00FF00FF,
+    0x0000FFFF
+};
+
+
+int get_bit_count(unsigned int x)
+{
+
+    int i;
+    int shift; /* Number of positions to shift to right*/
+    for (i = 0, shift = 1; i < 5; i++, shift *= 2) {
+        x = (x & mask[i])+ ((x >> shift) & mask[i]);
+    }
+    return x;
+}
+
+
+int main()
+{
+    int to_test[] = {0, 5, 7};
+    int current;
+
+    for (int i = 0; i < 3 ; i++) {
+        current = to_test[i];
+        printf("get_bit_count(%d) = %d\n", current, get_bit_count(current));
+    }
+}
+
+/* vim:filetype=c:fileencoding=utf-8
+ */