Fix precision 7 overflow

src/protobuf.js

@@ -6,19 +6,18 @@
 export function readVarInt64 (ta_struct) {
   let cursor = ta_struct.cursor
   let nVal = 0
-  let nShift = 0
+  let multiplier = 1
   let nByte
 
   while (true) {
     nByte = ta_struct.buffer[cursor]
+    cursor++
+    nVal += (nByte & 0x7f) * multiplier
     if ((nByte & 0x80) === 0) {
-      cursor++
       ta_struct.cursor = cursor
-      return nVal | (nByte << nShift)
+      return nVal
     }
-    nVal = nVal | (nByte & 0x7f) << nShift
-    cursor++
-    nShift += 7
+    multiplier *= 128
   }
 }
 
@@ -28,7 +27,7 @@ export function readVarSInt64 (ta_struct) {
 }
 
 export function unzigzag (nVal) {
-  if ((nVal & 1) === 0)
-    return nVal >> 1
-  return -(nVal >> 1) - 1
-}
+  if ((nVal % 2) === 0)
+    return nVal / 2
+  return -((nVal + 1) / 2)
+}

test/twkb.spec.js

@@ -23,6 +23,23 @@ describe('twkb', function () {
       })
     })
 
+    it('should decode precision=7 point in east Asia longitude range', function () {
+      // POINT(141.961144 35.681234) with precision 7
+      var g = twkb.toGeoJSON(Buffer.from('e100e0b4ecc90ae898a4d402', 'hex'))
+      assert.deepEqual(g, {
+         type: 'FeatureCollection',
+         features: [
+             {
+                type: 'Feature',
+                geometry: {
+                  type: 'Point',
+                  coordinates: [141.961144, 35.681234]
+                }
+             }
+         ]
+      })
+    })
+
     it('should decode linestring to geojson', function () {
       var g = twkb.toGeoJSON(Buffer.from('02000202020808', 'hex'))
       assert.deepEqual(g, {