[conversions] Fix toPrecision buffer length

pthier · V8 LUCI CQ · commit 245b6b0bc266 · 2025-01-09T03:59:09.000-08:00
Fixed: 386487312 Change-Id: I1247cafb0c27d2a1ea80c5c52e32926b07740ab4 Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/6162974 Auto-Submit: Patrick Thier <pthier@chromium.org> Reviewed-by: Leszek Swirski <leszeks@chromium.org> Commit-Queue: Leszek Swirski <leszeks@chromium.org> Cr-Commit-Position: refs/heads/main@{#98021}
diff --git a/src/numbers/conversions.cc b/src/numbers/conversions.cc
@@ -1196,10 +1196,6 @@ std::string_view DoubleToPrecisionStringView(double value, int p,
                                              exponent, negative, p, buffer);
   } else {
     // Use fixed notation.
-    //
-    // Leave room in the result for appending a minus, a period and in
-    // the case where decimal_point is not positive for a zero in
-    // front of the period.
     SimpleStringBuilder builder(buffer.begin(), buffer.length());
     if (negative) builder.AddCharacter('-');
     if (decimal_point <= 0) {
diff --git a/src/numbers/conversions.h b/src/numbers/conversions.h
@@ -72,10 +72,9 @@ constexpr int kDoubleToFixedMaxDigitsBeforePoint = 21;
 // Leave room in the result for appending a minus and a period.
 constexpr int kDoubleToFixedMaxChars =
     kDoubleToFixedMaxDigitsBeforePoint + kMaxFractionDigits + 2;
-// Leave room in the result for appending a minus, for a period, the
-// letter 'e', a minus or a plus depending on the exponent, and a
-// three digit exponent.
-constexpr int kDoubleToPrecisionMaxChars = kMaxFractionDigits + 7;
+// Leave room in the result for appending a minus, for a period, up to 5 zeros
+// padding after the period and a zero in front of the period.
+constexpr int kDoubleToPrecisionMaxChars = kMaxFractionDigits + 8;
 // Leave room in the result for one digit before the period, a minus, a period,
 // the letter 'e', a minus or a plus depending on the exponent, and a three
 // digit exponent.
diff --git a/test/mjsunit/regress/regress-386487312.js b/test/mjsunit/regress/regress-386487312.js
@@ -0,0 +1,7 @@
+// Copyright 2024 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+assertEquals(
+    '-0.000001234499999999999996546707660416419827242862083949148654937744140625000000000000000000000000000000000',
+    (-.0000012345).toPrecision(100));
