types: add Satoshi

src/types.js

@@ -6,6 +6,11 @@ function UInt31 (value) {
   return typeforce.UInt32(value) && value <= UINT31_MAX
 }
 
+var SATOSHI_MAX = 2.1 * 1e15
+function Satoshi (value) {
+  return typeforce.UInt53(value) && value <= SATOSHI_MAX
+}
+
 function Bip32Path (value) {
   return typeforce.String(value) &&
     value.match(/^(m\/)?(\d+'?\/)*\d+'?$/)
@@ -38,6 +43,7 @@ var types = {
   Hash160bit: typeforce.BufferN(20),
   Hash256bit: typeforce.BufferN(32),
   Network: Network,
+  Satoshi: Satoshi,
   UInt2: UInt2,
   UInt31: UInt31,
   Bip32Path: Bip32Path

test/types.js

@@ -46,4 +46,19 @@ describe('types', function () {
       }, /Expected Buffer\(Length: 32\), got Buffer\(Length: 20\)/)
     })
   })
+
+  describe('Satoshi', function () {
+    [
+      { value: -1, result: false },
+      { value: 0, result: true },
+      { value: 1, result: true },
+      { value: 20999999 * 1e8, result: true },
+      { value: 21000000 * 1e8, result: true },
+      { value: 21000001 * 1e8, result: false }
+    ].forEach(function (f) {
+      it('returns ' + f.result + ' for valid for ' + f.value, function () {
+        assert.strictEqual(types.Satoshi(f.value), f.result)
+      })
+    })
+  })
 })