Fix floating point issues on Windows.

runtime/platform/floating_point_win.cc

Index: runtime/platform/floating_point_win.cc
diff --git a/runtime/platform/floating_point_win.cc b/runtime/platform/floating_point_win.cc
new file mode 100644
index 0000000000000000000000000000000000000000..bb34d9bc293a4d1ffb7f3206b23197e4401941f8
--- /dev/null
+++ b/runtime/platform/floating_point_win.cc
@@ -0,0 +1,44 @@
+// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+#include <math.h>
+#include <limits>
+
+#include "platform/globals.h"
+
+// Taken from third_party/v8/src/platform-win32.cc
+double modulo(double x, double y) {
+  // Work around MS fmod bugs. ISO Standard says:
+  // dividend is finite and divisor is an infinity => result equals dividend

[Mads Ager (google), 2012/11/29 09:36:36]

Nit picking: could you start with a capital letter and end with a period?

I like the list style you have below. Can you use that here as well:

 - Dividend is finite and divisor is an infinity => result equals dividend.

[aam-me, 2012/11/29 12:39:53]

Done.

+  // dividend is a zero and divisor is nonzero finite => result equals dividend
+  if (!(_finite(x) && (!_finite(y) && !isnan(y))) &&
+      !(x == 0 && (y != 0 && _finite(y)))) {
+    x = fmod(x, y);
+  }
+  return x;
+}
+
+// Bring MSVC atan2 behavior in line with ISO standard.
+// MSVC atan2 returns NaN when x and y are either +inf or -inf.
+// Per ISO standard:
+//  - If y is +inf(-infinity) and x is -inf, +3*pi/4 (-3*pi/4) is returned.

[Mads Ager (google), 2012/11/29 09:36:36]

Could you write out 'infinity' for all occurrences here and below.

[aam-me, 2012/11/29 12:39:53]

Done.

+//  - If y is +inf(-infinity) and x is +inf, +pi/4 (-pi/4) is returned.
+double atan2_ieee(double x, double y) {
+  int cls_x = _fpclass(x);
+  int cls_y = _fpclass(y);
+  if (((cls_x & (_FPCLASS_PINF | _FPCLASS_NINF)) != 0) &&
+      ((cls_y & (_FPCLASS_PINF | _FPCLASS_NINF)) != 0)) {
+    // atan2 values at infinities listed above are the same as values
+    // at (+/-1, +/-1). ndx_x is 0, when x is +inf, 1 when x is -inf.
+    // Same is with ndx_y.
+    int ndx_x = (cls_x & _FPCLASS_PINF) != 0? 0: 1;

[Mads Ager (google), 2012/11/29 09:36:36]

Please add spaces and write out index:

int index_x = (...) != 0 ? 0 : 1;
int index_y = (...) != 0 ? 0 : 1;

[aam-me, 2012/11/29 12:39:53]

Done.

+    int ndx_y = (cls_y & _FPCLASS_PINF) != 0? 0: 1;
+    static double atans_at_infinities[2][2] =
+      { { atan2(1.,  1.), atan2(1.,  -1.) },
+        { atan2(-1., 1.), atan2(-1., -1.) } };
+    return atans_at_infinities[ndx_x][ndx_y];
+  } else {
+    return atan2(x, y);
+  }
+}