New bigint implementation in the vm.

runtime/lib/math.cc

Index: runtime/lib/math.cc
===================================================================
--- runtime/lib/math.cc	(revision 40060)
+++ runtime/lib/math.cc	(working copy)
@@ -6,7 +6,6 @@
 
 #include "vm/bootstrap_natives.h"
 
-#include "vm/bigint_operations.h"
 #include "vm/exceptions.h"
 #include "vm/native_entry.h"
 #include "vm/object.h"
@@ -153,26 +152,34 @@
   GET_NON_NULL_NATIVE_ARGUMENT(Integer, seed_int, arguments->NativeArgAt(0));
   uint64_t seed = 0;
   if (seed_int.IsBigint()) {
-    const Bigint& mask64 = Bigint::Handle(
-        BigintOperations::NewFromUint64(0xffffffffffffffffLL));
     Bigint& big_seed = Bigint::Handle();
     big_seed ^= seed_int.raw();
     uint64_t negate_mask = 0;
+    uint64_t borrow = 0;
     if (big_seed.IsNegative()) {
       // Negate bits to make seed positive.
       // Negate bits again (by xor with negate_mask) when extracted below,
       // to get original bits.
       negate_mask = 0xffffffffffffffffLL;
-      big_seed ^= BigintOperations::BitNot(big_seed);
+
+      // Instead of computing ~big_seed here, we compute it on the fly below as
+      // follows: ~(-big_seed) == ~(~(big_seed-1)) == big_seed-1
+      borrow = 1;
     }
-    Bigint& low64 = Bigint::Handle();
+    const intptr_t used = big_seed.Used();
+    intptr_t digit = 0;
     do {
-      low64 = BigintOperations::BitAnd(big_seed, mask64);
-      ASSERT(BigintOperations::FitsIntoUint64(low64));
-      uint64_t chunk = BigintOperations::ToUint64(low64) ^ negate_mask;
-      seed = (seed * 1037) ^ mix64(chunk);
-      big_seed = BigintOperations::ShiftRight(big_seed, 64);
-    } while (!big_seed.IsZero());
+      uint64_t low64 = ((digit + 1) < used) ? big_seed.DigitAt(digit + 1) : 0;
+      low64 <<= 32;
+      low64 |= (digit < used) ? big_seed.DigitAt(digit) : 0;
+      low64 -= borrow;
+      if ((borrow == 1) && (low64 != 0xffffffffffffffffLL)) {
+        borrow = 0;
+      }
+      low64 ^= negate_mask;
+      seed = (seed * 1037) ^ mix64(low64);
+      digit += 2;
+    } while (digit < used);
   } else {
     seed = mix64(static_cast<uint64_t>(seed_int.AsInt64Value()));
   }