script_number: refactor

src/script_number.js

@@ -11,38 +11,38 @@ function decode (buffer, maxLength, minimal) {
     }
   }
 
-  // 32-bit?
+  var result
-  if (length < 5) {
-    var result = 0
 
-    for (var i = 0; i < length; ++i) {
+  // 40-bit
-      result += buffer[i] << (8 * i)
+  if (length === 5) {
+    var a = buffer.readUInt32LE(0)
+    var b = buffer.readUInt8(4)
+
+    if (b & 0x80) return -((b & ~0x80) * 0x100000000 + a)
+    return b * 0x100000000 + a
+
+  // 32-bit
+  } else if (length === 4) {
+    result = buffer.readUInt32LE(0)
+
+  // 24-bit
+  } else if (length === 3) {
+    result = buffer.readUInt16LE(0)
+    result |= buffer.readUInt8(2) << 16
+
+  // 16-bit
+  } else if (length === 2) {
+    result = buffer.readUInt16LE(0)
+
+  // 8-bit
+  } else {
+    result = buffer.readUInt8(0)
   }
 
   if (buffer[length - 1] & 0x80) return -(result & ~(0x80 << (8 * (length - 1))))
   return result
 }
 
-  // 40-bit
-  var a = buffer.readUInt32LE(0)
-  var b = buffer.readUInt8(4)
-
-  // TODO: refactor
-  var neg = false
-  if (b & 0x80) {
-    b &= ~0x80
-    neg = true
-  }
-
-  var r = b * 0x100000000 + a
-
-  if (neg) {
-    r = -r
-  }
-
-  return r
-}
-
 function scriptNumSize (i) {
   return i > 0x7fffffff ? 5
   : i > 0x7fffff ? 4