Implement Double.toStringAsFixed.

runtime/vm/double_conversion.cc

Index: runtime/vm/double_conversion.cc
diff --git a/runtime/vm/double_conversion.cc b/runtime/vm/double_conversion.cc
new file mode 100644
index 0000000000000000000000000000000000000000..7ec022f299a5503400130c67c7bc01c8f30f8d5a
--- /dev/null
+++ b/runtime/vm/double_conversion.cc
@@ -0,0 +1,150 @@
+// Copyright (c) 2011, 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 "vm/double_conversion.h"
+
+#include "third_party/double-conversion/src/double-conversion.h"
+
+#include "vm/exceptions.h"
+#include "vm/globals.h"
+#include "vm/object.h"
+
+namespace dart {
+
+static const char kDoubleToStringCommonExponentChar = 'e';
+static const char* kDoubleToStringCommonInfinitySymbol = "Infinity";
+static const char* kDoubleToStringCommonNaNSymbol = "NaN";
+
+bool DoubleToString(double d, String& result) {
+  static const int kDecimalLow = -6;
+  static const int kDecimalHigh = 21;
+  static const int kConversionFlags =
+      double_conversion::DoubleToStringConverter::EMIT_POSITIVE_EXPONENT_SIGN |
+      double_conversion::DoubleToStringConverter::EMIT_TRAILING_DECIMAL_POINT |
+     double_conversion::DoubleToStringConverter::EMIT_TRAILING_ZERO_AFTER_POINT;
+  const int kBufferSize = 128;
+  // The output contains the sign, at most kDecimalHigh - 1 digits,
+  // the decimal point followed by a 0 plus the \0.
+  ASSERT(kBufferSize >= 1 + (kDecimalHigh - 1) + 1 + 1 + 1);
+  // Or it contains the sign, a 0, the decimal point, kDecimalLow '0's,
+  // 17 digits (the precision needed for doubles), plus the \0.
+  ASSERT(kBufferSize >= 1 + 1 + 1 + kDecimalLow + 17 + 1);
+  // Alternatively it contains a sign, at most 17 digits (precision needed for
+  // any double), the decimal point, the exponent character, the exponent's
+  // sign, at most three exponent digits, plus the \0.
+  ASSERT(kBufferSize >= 1 + 17 + 1 + 1 + 1 + 3 + 1);
+
+  const double_conversion::DoubleToStringConverter converter(
+      kConversionFlags,
+      kDoubleToStringCommonInfinitySymbol,
+      kDoubleToStringCommonNaNSymbol,
+      kDoubleToStringCommonExponentChar,
+      kDecimalLow,
+      kDecimalHigh,
+      0, 0);  // Last two values are ignored in shortest mode.
+
+  UNIMPLEMENTED();
+  return false;
+}
+
+bool DoubleToStringAsFixed(double d, int fraction_digits, String& result) {
+  static const int kMinFractionDigits = 0;
+  static const int kMaxFractionDigits = 20;
+  static const int kMaxDigitsBeforePoint = 20;
+  // The boundaries are exclusive.
+  static const double kLowerBoundary = -1e21;
+  static const double kUpperBoundary = 1e21;
+  static const int kConversionFlags =
+      double_conversion::DoubleToStringConverter::NO_FLAGS;
+  const int kBufferSize = 128;
+  // The output contains the sign, at most kMaxDigitsBeforePoint digits,
+  // the decimal point followed by at most fraction_digits digits plus the \0.
+  ASSERT(kBufferSize >= 1 + kMaxDigitsBeforePoint + 1 + kMaxFractionDigits + 1);
+
+  if (!(isnan(d) || (kLowerBoundary < d && d < kUpperBoundary))) {

[Ivan Posva, 2011/12/20 00:30:03]

You could add an early bailout for NaN and return a canonicalized string "NaN"
instead of going through the full machinery below. You could even test that
before entering into the native code on the Dart side.

[floitsch, 2011/12/22 21:53:20]

Added early bailout in dart-land.
Done.

+    return false;
+  }
+  if (!(kMinFractionDigits <= fraction_digits &&

[Ivan Posva, 2011/12/20 00:30:03]

Might be personal style, but I prefer not to have large expressions negated.
Same above...

[floitsch, 2011/12/22 21:53:20]

Done.

+        fraction_digits <= kMaxFractionDigits)) {
+    return false;
+  }
+
+  const double_conversion::DoubleToStringConverter converter(
+      kConversionFlags,
+      kDoubleToStringCommonInfinitySymbol,
+      kDoubleToStringCommonNaNSymbol,
+      kDoubleToStringCommonExponentChar,
+      0, 0, 0, 0);  // Last four values are ignored in fixed mode.
+
+  char buffer[kBufferSize];
+  double_conversion::StringBuilder builder(buffer, kBufferSize);
+  bool status = converter.ToFixed(d, fraction_digits, &builder);
+  if (!status) return false;
+  int length = builder.position();
+  result ^= String::New(reinterpret_cast<uint8_t*>(builder.Finalize()), length);
+  return true;
+}
+
+
+bool DoubleToStringAsExponential(double d,
+                                 int fraction_digits,
+                                 String& result) {
+  static const int kMinFractionDigits = 0;
+  static const int kMaxFractionDigits = 20;
+  static const int kConversionFlags =
+      double_conversion::DoubleToStringConverter::EMIT_POSITIVE_EXPONENT_SIGN;
+  const int kBufferSize = 128;
+  // The output contains the sign, at most 1 digits, the decimal point followed
+  // by at most kMaxFractionDigits digits, the exponent-character, the
+  // exponent-sign and three exponent digits plus \0.
+  ASSERT(kBufferSize >= 1 + 1 + kMaxFractionDigits + 1 + 1 + 3 + 1);
+
+  if (!(kMinFractionDigits <= fraction_digits &&
+        fraction_digits <= kMaxFractionDigits)) {
+    return false;
+  }
+
+  const double_conversion::DoubleToStringConverter converter(
+      kConversionFlags,
+      kDoubleToStringCommonInfinitySymbol,
+      kDoubleToStringCommonNaNSymbol,
+      kDoubleToStringCommonExponentChar,
+      0, 0, 0, 0);  // Last four values are ignored in exponential mode.
+
+  UNIMPLEMENTED();
+  return false;
+}
+
+
+bool DoubleToStringAsPrecision(double d, int precision, String& result) {
+  static const int kMinPrecisionDigits = 1;
+  static const int kMaxPrecisionDigits = 21;
+  static const int kMaxLeadingPaddingZeroes = 6;
+  static const int kMaxTrailingPaddingZeroes = 0;
+  static const int kConversionFlags =
+      double_conversion::DoubleToStringConverter::EMIT_POSITIVE_EXPONENT_SIGN;
+  const int kBufferSize = 128;
+  // The output contains the sign, the decimal point, precision digits,
+  // the exponent-character, the exponent-sign, three exponent digits
+  // plus the \0.
+  ASSERT(kBufferSize >= 1 + 1 + kMaxPrecisionDigits + 1 + 1 + 3 + 1);
+
+  if (!(kMinPrecisionDigits <= precision && precision <= kMaxPrecisionDigits)) {
+    return false;
+  }
+
+  const double_conversion::DoubleToStringConverter converter(
+      kConversionFlags,
+      kDoubleToStringCommonInfinitySymbol,
+      kDoubleToStringCommonNaNSymbol,
+      kDoubleToStringCommonExponentChar,
+      0, 0,  // Ignored in precision mode.
+      kMaxLeadingPaddingZeroes,
+      kMaxTrailingPaddingZeroes);
+
+  UNIMPLEMENTED();
+  return false;
+}
+
+}  // namespace dart