commit 949f122a742fffa8019acbae4f09b16ce694e837
Author: David Sorber <david.sorber@gmail.com>
Date:   Thu Oct 29 15:34:27 2015 -0400

    Added a third bit position approach and created a script for making sparse vectors.

diff --git a/software/misc/bit_position/bit_position.c b/software/misc/bit_position/bit_position.c
index 22724f8..dc0ede9 100644
--- a/software/misc/bit_position/bit_position.c
+++ b/software/misc/bit_position/bit_position.c
@@ -15,7 +15,7 @@
 
 int timeval_subtract(struct timeval *result, struct timeval *x, struct timeval *y)
 {
-    /* Perform the carry for the later subtraction by updating y. */
+    // Perform the carry for the later subtraction by updating yy
     if (x->tv_usec < y->tv_usec) {
         int nsec = (y->tv_usec - x->tv_usec) / 1000000 + 1;
         y->tv_usec -= 1000000 * nsec;
@@ -26,11 +26,11 @@ int timeval_subtract(struct timeval *result, struct timeval *x, struct timeval *
         y->tv_usec += 1000000 * nsec;
         y->tv_sec -= nsec;
     }
-    /* Compute the time remaining to wait.
-     tv_usec is certainly positive. */
+    // Compute the time remaining to wait. tv_usec is certainly positive.
     result->tv_sec = x->tv_sec - y->tv_sec;
     result->tv_usec = x->tv_usec - y->tv_usec;
-    /* Return 1 if result is negative. */
+    
+    // Return 1 if result is negative.
     return x->tv_sec < y->tv_sec;
 }
 
@@ -40,21 +40,22 @@ void approach0(uint32_t count, uint64_t* vectors)
     for (uint32_t idx = 0; idx < count; idx++) {
         uint64_t copy = vectors[idx];
         
-        printf("Index: %" PRIu32 "\n", idx);
+        //~ printf("Index: %" PRIu32 "\n", idx);
         
         uint64_t compare = 1;
-            
+        uint64_t position = 0;    
         for (uint32_t ctr = 0; ctr < 64; ctr++)
         {
             if (compare & copy)
             {
-                printf("%" PRIu32 " ", ctr);
+                uint64_t position = ctr;
+                //~ printf("%" PRIu32 " ", ctr);
             }
             
             compare = (compare << 1);
         }
         
-        printf("\n\n");
+        //~ printf("\n\n");
     }
 }
 
@@ -64,16 +65,16 @@ void approach1(uint32_t count, uint64_t* vectors)
     for (uint32_t idx = 0; idx < count; idx++) {
         uint64_t copy = vectors[idx];
         
-        printf("Index: %" PRIu32 "\n", idx);
+        //~ printf("Index: %" PRIu32 "\n", idx);
         
         uint64_t position = 0;
         while (copy) {
             position = __builtin_ctzll(copy);
-            printf("%" PRIu64 " ", position);
+            //~ printf("%" PRIu64 " ", position);
             copy &= ~((uint64_t)1 << position);
         }
         
-        printf("\n\n");
+        //~ printf("\n\n");
     }
 }
 
@@ -149,16 +150,37 @@ void approach2(uint32_t count, uint64_t* vectors)
     for (uint32_t idx = 0; idx < count; idx++) {
         uint64_t copy = vectors[idx];
         
-        printf("Index: %" PRIu32 "\n", idx);
+        //~ printf("Index: %" PRIu32 "\n", idx);
         
         uint64_t position = 0;
         while (copy) {
             position = __builtin_ctzll(copy);
-            printf("%" PRIu64 " ", position);
+            //~ printf("%" PRIu64 " ", position);
             copy &= masks[position];
         }
         
-        printf("\n\n");
+        //~ printf("\n\n");
+    }
+}
+
+// Approach 3: use intrinsic and 2's complement trick
+void approach3(uint32_t count, uint64_t* vectors)
+{
+    for (uint32_t idx = 0; idx <   I wcount; idx++) {
+        uint64_t copy = vectors[idx];
+        uint64_t vector = copy & (~copy + 1);
+        
+        //~ printf("Index: %" PRIu32 "\n", idx);
+        
+        uint64_t position = 0;
+        while (vector) {
+            position = __builtin_ffsll(vector);
+            //~ printf("%" PRIu64 " ", position);
+            copy = ~vector & copy;
+            vector = copy & (~copy + 1);
+        }
+        
+        //~ printf("\n\n");
     }
 }
 
@@ -168,7 +190,7 @@ int main(int argc, char** argv)
     // was specified
     if (argc < 3) {
         fprintf(stderr, "Please specify file containing vectors and approach "
-                        "index (0-2)\n");
+                        "index (0-3)\n");
         return -1;
     }
     
@@ -209,6 +231,9 @@ int main(int argc, char** argv)
         case '2':
             approach2(count, vectors);
             break;
+        case '3':
+            approach3(count, vectors);
+            break;
         default:
             fprintf(stderr, "ERROR: invalid approach index\n");
     }
diff --git a/software/misc/bit_position/make_sparse_vectors.py b/software/misc/bit_position/make_sparse_vectors.py
new file mode 100755
index 0000000..47e0769
--- /dev/null
+++ b/software/misc/bit_position/make_sparse_vectors.py
@@ -0,0 +1,33 @@
+#!/usr/bin/python3
+import random
+import sys
+
+def main():
+    
+    if len(sys.argv) < 3:
+        print('ERROR: must specify sparsity and number of output vectors')
+        return 1
+    
+    sparsity = 0
+    try:
+        sparsity = int(sys.argv[1])
+    except ValueError:
+        print('ERROR: sparsity argument must be an integer')
+        return 1
+    
+    num_vectors = 0
+    try:
+        num_vectors = int(sys.argv[2])
+    except ValueError:
+        print('ERROR: number of vectors argument must be an integer')
+        return 1
+    
+    random.seed()
+    for idx in range(num_vectors):
+        vector = 0
+        for num_bits in range(random.randint(0, sparsity)):
+            vector |= (1 << random.randint(0, 63));
+        print('{:016X}'.format(vector))
+    
+if __name__ == '__main__':
+    sys.exit(main())
diff --git a/software/misc/bit_position/make_vectors.py b/software/misc/bit_position/make_vectors.py
old mode 100644
new mode 100755
index 1f25625..231a991
--- a/software/misc/bit_position/make_vectors.py
+++ b/software/misc/bit_position/make_vectors.py
@@ -1,3 +1,4 @@
+#!/usr/bin/python3
 import sys
 
 def main():