Fast algorithm for double->string conversion.

test/cctest/test-diy_fp.cc

Index: test/cctest/test-diy_fp.cc
===================================================================
--- test/cctest/test-diy_fp.cc	(revision 0)
+++ test/cctest/test-diy_fp.cc	(revision 0)
@@ -0,0 +1,77 @@
+// Copyright 2006-2008 the V8 project authors. All rights reserved.
+
+#include <stdlib.h>
+
+#include "v8.h"
+
+#include "platform.h"
+#include "cctest.h"
+#include "diy_fp.h"
+
+using namespace v8::internal;
+
+
+TEST(Subtract) {
+  DiyFp diy_fp1 = DiyFp(3, 0);
+  DiyFp diy_fp2 = DiyFp(1, 0);
+  DiyFp diff = DiyFp::Minus(diy_fp1, diy_fp2);
+  uint64_t correct_f;
+
+  correct_f = 2;
+  CHECK_EQ(correct_f, diff.f());
+  CHECK_EQ(0, diff.e());
+  diy_fp1.Subtract(diy_fp2);
+  correct_f = 2;
+  CHECK_EQ(correct_f, diy_fp1.f());
+  CHECK_EQ(0, diy_fp1.e());
+}
+
+
+TEST(Multiply) {
+  uint64_t correct_f;
+
+  DiyFp diy_fp1 = DiyFp(3, 0);
+  DiyFp diy_fp2 = DiyFp(2, 0);
+  DiyFp product = DiyFp::Times(diy_fp1, diy_fp2);
+  correct_f = 0;
+  CHECK_EQ(correct_f, product.f());
+  CHECK_EQ(64, product.e());
+  diy_fp1.Multiply(diy_fp2);
+  correct_f = 0;
+  CHECK_EQ(correct_f, diy_fp1.f());
+  CHECK_EQ(64, diy_fp1.e());
+
+  diy_fp1 = DiyFp(V8_2PART_UINT64_C(0x80000000,00000000), 11);
+  diy_fp2 = DiyFp(2, 13);
+  product = DiyFp::Times(diy_fp1, diy_fp2);
+  correct_f = 1;
+  CHECK_EQ(correct_f, product.f());
+  CHECK_EQ(11 + 13 + 64, product.e());
+
+  // Test rounding.
+  diy_fp1 = DiyFp(V8_2PART_UINT64_C(0x80000000,00000001), 11);
+  diy_fp2 = DiyFp(1, 13);
+  product = DiyFp::Times(diy_fp1, diy_fp2);
+  correct_f = 1;
+  CHECK_EQ(correct_f, product.f());
+  CHECK_EQ(11 + 13 + 64, product.e());
+
+  diy_fp1 = DiyFp(V8_2PART_UINT64_C(0x7fffffff,ffffffff), 11);
+  diy_fp2 = DiyFp(1, 13);
+  product = DiyFp::Times(diy_fp1, diy_fp2);
+  correct_f = 0;
+  CHECK_EQ(correct_f, product.f());
+  CHECK_EQ(11 + 13 + 64, product.e());
+
+  // Halfway cases are allowed to round either way. So don't check for it.
+
+  // Big numbers.
+  diy_fp1 = DiyFp(V8_2PART_UINT64_C(0xFFFFFFFF,FFFFFFFF), 11);
+  diy_fp2 = DiyFp(V8_2PART_UINT64_C(0xFFFFFFFF,FFFFFFFF), 13);
+  // 128bit result: 0xfffffffffffffffe0000000000000001
+  product = DiyFp::Times(diy_fp1, diy_fp2);
+  correct_f = V8_2PART_UINT64_C(0xFFFFFFFF,FFFFFFFe);
+  CHECK_EQ(correct_f, product.f());
+  CHECK_EQ(11 + 13 + 64, product.e());
+
+}