1 files changed, 10 insertions, 0 deletions
diff --git a/src/runtime.js b/src/runtime.js
index 6439d0ed..6f17028a 100644
--- a/src/runtime.js
+++ b/src/runtime.js
@@ -73,6 +73,15 @@ var RuntimeGenerator = {
       quantum = '(quantum ? quantum : {{{ QUANTUM_SIZE }}})';
     }
     return target + ' = ' + Runtime.forceAlign(target, quantum);
+  },
+
+  // Given two 32-bit unsigned parts of an emulated 64-bit number, combine them into a JS number (double).
+  // Rounding is inevitable if the number is large. This is a particular problem for small negative numbers
+  // (-1 will be rounded!), so handle negatives separately and carefully
+  makeBigInt: function(low, high, unsigned) {
+    return '(' + unsigned +
+           ' ? (' + makeSignOp(low, 'i32', 'un', 1, 1) + '+(' + makeSignOp(high, 'i32', 'un', 1, 1) + '*4294967296))' +
+           ' : (' + makeSignOp(low, 'i32', 'un', 1, 1) + '+(' + makeSignOp(high, 'i32', 're', 1, 1) + '*4294967296)))';
   }
 };
 
@@ -260,6 +269,7 @@ var Runtime = {
 Runtime.stackAlloc = unInline('stackAlloc', ['size']);
 Runtime.staticAlloc = unInline('staticAlloc', ['size']);
 Runtime.alignMemory = unInline('alignMemory', ['size', 'quantum']);
+Runtime.makeBigInt = unInline('makeBigInt', ['low', 'high', 'unsigned']);
 
 function getRuntime() {
   var ret = 'var Runtime = {\n';