add if/notif/else/endif opcodes.

lib/bcoin/script.js

@@ -130,7 +130,30 @@ script.verify = function verify(hash, sig, pub) {
   }
 };
 
+script._next = function(to, s, pc) {
+  var depth = 0;
+  while (s[pc]) {
+    var o = s[pc];
+    if (o === 'if_' || o === 'notif')
+      depth++;
+    else if (o === 'else')
+      depth--;
+    else if (o === 'endif')
+      depth--;
+    if (depth < 0)
+      break;
+    if (depth === 0 && o === to)
+      return pc;
+    if (o === 'else')
+      depth++;
+    pc++;
+  }
+  return -1;
+};
+
 script.execute = function execute(s, stack, tx, index) {
+  s = s.slice();
+
   if (s.length > 10000)
     return false;
 
@@ -153,6 +176,47 @@ script.execute = function execute(s, stack, tx, index) {
     }
 
     switch (o) {
+      case 'if_':
+      case 'notif': {
+        var val = false;
+        if (stack.length < 1)
+          return false;
+        var v = stack.pop();
+        val = new bn(v).cmp(0) !== 0;
+        if (o === 'notif')
+          val = !val;
+        var if_ = pc;
+        var else_ = script._next('else_', s, pc);
+        var endif = script._next('endif', s, pc);
+        // Splice out the statement blocks we don't need
+        if (val) {
+          if (endif === -1)
+            return false;
+          if (else_ === -1) {
+            s.splice(endif, 1);
+            s.splice(if_, 1);
+          } else {
+            s.splice(else_, (endif - else_) + 1);
+            s.splice(if_, 1);
+          }
+        } else {
+          if (endif === -1)
+            return false;
+          if (else_ === -1)
+            s.splice(if_, (endif - if_) + 1);
+          else
+            s.splice(if_, (else_ - if_) + 1);
+        }
+        // Subtract one since we removed the if/notif opcode
+        pc--;
+        break;
+      }
+      case 'else_': {
+        return false;
+      }
+      case 'endif': {
+        return false;
+      }
       case 'dup': {
         if (stack.length === 0)
           return false;