Add methods for creating Bigint objects from unsigned 64-bit integers.

runtime/vm/bigint_operations.cc

Index: runtime/vm/bigint_operations.cc
diff --git a/runtime/vm/bigint_operations.cc b/runtime/vm/bigint_operations.cc
index 820562f56a32420a5064b4f5344ec27c054681f5..8a5d257fc83d73a994f57a960647a9f3f9cf8f0c 100644
--- a/runtime/vm/bigint_operations.cc
+++ b/runtime/vm/bigint_operations.cc
@@ -73,6 +73,14 @@ RawBigint* BigintOperations::NewFromInt64(int64_t value, Heap::Space space) {
     value = -value;
   }
 
+  const Bigint& result = Bigint::Handle(NewFromUInt64(value, space));
+  result.SetSign(is_negative);
+
+  return result.raw();
+}
+
+
+RawBigint* BigintOperations::NewFromUInt64(uint64_t value, Heap::Space space) {
   const int kNumBytes = sizeof(value);
   unsigned char pch[kNumBytes];
   for (int i = kNumBytes - 1; i >= 0; i--) {
@@ -80,13 +88,8 @@ RawBigint* BigintOperations::NewFromInt64(int64_t value, Heap::Space space) {
     value >>=8;
     pch[i] = c;
   }
-
   BN_bin2bn(pch, kNumBytes, TmpBN());
-
-  const Bigint& result = Bigint::Handle(Bigint::New(TmpBN(), space));
-  result.SetSign(is_negative);
-
-  return result.raw();
+  return Bigint::New(TmpBN(), space);
 }
 
 
@@ -330,6 +333,31 @@ int64_t BigintOperations::ToInt64(const Bigint& bigint) {
 }
 
 
+bool BigintOperations::FitsIntoUInt64(const Bigint& bigint) {
+  const BIGNUM *bn = bigint.BNAddr();
+  if (bigint.IsNegative()) return false;
+  int bits = BN_num_bits(bn);
+  if (bits > 64) return false;
+  return true;
+}
+
+
+uint64_t BigintOperations::ToUInt64(const Bigint& bigint) {
+  ASSERT(FitsIntoUInt64(bigint));
+  unsigned char bytes[8];
+  ASSERT(BN_num_bytes(bigint.BNAddr()) <= static_cast<int>(sizeof bytes));
+  int n = BN_bn2bin(bigint.BNAddr(), bytes);
+  ASSERT(n >= 0);
+  int64_t value = 0;
+  ASSERT(n <= static_cast<int>(sizeof value));
+  for (int i = 0; i < n; ++i) {
+    value <<= 8;
+    value |= bytes[i];
+  }

[siva, 2011/11/12 01:20:07]

This code here seems identical to ToInt64 except the initial ASSERT and the
final check for bigint.IsNegative.
Maybe the command code can be factored into a static method.

[cshapiro, 2011/11/12 01:50:09]

Good idea.  I am not sure how I missed that.  Done.

+  return value;
+}
+
+
 RawBigint* BigintOperations::Add(const Bigint& a, const Bigint& b) {
   int status = BN_add(TmpBN(), a.BNAddr(), b.BNAddr());
   ASSERT(status == 1);