Add difference operation.

src/meryl/meryl-args.C

@@ -421,6 +421,8 @@ merylArgs::merylArgs(int argc, char **argv) {
         personality = PERSONALITY_ADD;
       } else if (strcmp(argv[arg], "sub") == 0) {
         personality = PERSONALITY_SUB;
+      } else if (strcmp(argv[arg], "difference") == 0) {
+        personality = PERSONALITY_DIFFERENCE;
       } else if (strcmp(argv[arg], "abs") == 0) {
         personality = PERSONALITY_ABS;
       } else if (strcmp(argv[arg], "divide") == 0) {

src/meryl/meryl-binaryOp.C

@@ -64,6 +64,7 @@ binaryOperations(merylArgs *args) {
     exit(1);
   }
   if ((args->personality != PERSONALITY_SUB) &&
+      (args->personality != PERSONALITY_DIFFERENCE) &&
       (args->personality != PERSONALITY_ABS) &&
       (args->personality != PERSONALITY_DIVIDE)) {
     fprintf(stderr, "ERROR - only personalities sub and abs\n");
@@ -146,6 +147,43 @@ binaryOperations(merylArgs *args) {
         }
       }
       break;
+    case PERSONALITY_DIFFERENCE:
+      while (A->validMer() || B->validMer()) {
+        Amer = A->theFMer();
+        Acnt = A->theCount();
+        Bmer = B->theFMer();
+        Bcnt = B->theCount();
+
+        //  If A stream is out of mers, do nothing but read the B stream.
+        if (A->validMer() == false) {
+          B->nextMer();
+          continue;
+        }
+
+        //  If B stream is out of mers, output the A mer.
+        if (B->validMer() == false) {
+          W->addMer(Amer, Acnt);
+          A->nextMer();
+          continue;
+        }
+
+        //  If the same mer, do nothing but read new mers.
+        if (Amer == Bmer) {
+          A->nextMer();
+          B->nextMer();
+          continue;
+        }
+
+        //  If A is before B, output A and read a new one.
+        //  Otherwise, do nothing and read a new one.
+        if (Amer < Bmer) {
+          W->addMer(Amer, Acnt);
+          A->nextMer();
+        } else {
+          B->nextMer();
+        }
+      }
+      break;
     case PERSONALITY_ABS:
       while (A->validMer() || B->validMer()) {
         Amer = A->theFMer();

src/meryl/meryl.C

@@ -88,6 +88,7 @@ main(int argc, char **argv) {
       break;
 
     case PERSONALITY_SUB:
+    case PERSONALITY_DIFFERENCE:
     case PERSONALITY_ABS:
     case PERSONALITY_DIVIDE:
       binaryOperations(args);

src/meryl/meryl.H

@@ -64,8 +64,9 @@
 #define PERSONALITY_MAXEXIST      0x04
 #define PERSONALITY_ADD           0x05
 #define PERSONALITY_SUB           0x06
-#define PERSONALITY_DIVIDE        0x07
-#define PERSONALITY_ABS           0x08
+#define PERSONALITY_DIFFERENCE    0x07
+#define PERSONALITY_DIVIDE        0x08
+#define PERSONALITY_ABS           0x09
 
 #define PERSONALITY_AND           0x10
 #define PERSONALITY_NAND          0x11