a more verbose version of the bit counter

gowrikumar/src/07b-countbits.c

@@ -0,0 +1,67 @@
+/**
+ * :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)
+{
+    printf("get_bit_count(%d)\n", x);
+
+    int i;
+    int x_and_mask;
+    int x_shifted;
+    int x_shifted_and_mask;
+    int shift; /* Number of positions to shift to right*/
+    for (i = 0, shift = 1; i < 5; i++, shift *= 2) {
+        printf("    START loop\n");
+        printf("        i = %d, x = %d, shift = %d\n", i, x, shift);
+
+        x_and_mask = x & mask[i];
+        printf("        x & mask[i] = %d\n", x_and_mask);
+
+        x_shifted = x >> shift;
+        printf("        x >> shift = %d\n", x_shifted);
+
+        x_shifted_and_mask = x_shifted & mask[i];
+        printf("        (x >> shift) & mask[i] = %d\n", x_shifted_and_mask);
+
+        x = x_and_mask + x_shifted_and_mask;
+        printf("        x = %d\n", x);
+        printf("    END loop\n");
+    }
+
+    return x;
+}
+
+
+int main()
+{
+    int to_test[] = {0, 5, 7};
+    int current;
+
+    /*
+    size_t mask_len = sizeof(mask) / sizeof(unsigned int);
+
+    for (int i = 0; i < mask_len; i++) {
+        printf("mask[%d] = %d\n", i, mask[i]);
+    }
+    */
+
+    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
+ */