From 1ce8615345a0167b8307b6390950dcd91aa2abc8 Mon Sep 17 00:00:00 2001
From: zhenyipeng <zhenyipeng@tencent.com>
Date: Thu, 1 Aug 2019 12:02:08 +0800
Subject: [PATCH] Add min exponent width option in double-to-string shortest
 conversion

---
 double-conversion/double-to-string.cc |  5 +++++
 double-conversion/double-to-string.h  |  7 +++++--
 test/cctest/test-conversions.cc       | 30 +++++++++++++++++++++++++++
 3 files changed, 40 insertions(+), 2 deletions(-)

diff --git a/double-conversion/double-to-string.cc b/double-conversion/double-to-string.cc
index 13c7110..e708097 100644
--- a/double-conversion/double-to-string.cc
+++ b/double-conversion/double-to-string.cc
@@ -105,6 +105,11 @@ void DoubleToStringConverter::CreateExponentialRepresentation(
     buffer[--first_char_pos] = '0' + (exponent % 10);
     exponent /= 10;
   }
+  // Add prefix '0' to make exponent width >= min(min_exponent_with_, kMaxExponentLength)
+  // For example: convert 1e+9 -> 1e+09, if min_exponent_with_ is set to 2
+  while(kMaxExponentLength - first_char_pos < std::min(min_exponent_width_, kMaxExponentLength)) {
+    buffer[--first_char_pos] = '0';
+  }
   result_builder->AddSubstring(&buffer[first_char_pos],
                                kMaxExponentLength - first_char_pos);
 }
diff --git a/double-conversion/double-to-string.h b/double-conversion/double-to-string.h
index c1be34d..194f80b 100644
--- a/double-conversion/double-to-string.h
+++ b/double-conversion/double-to-string.h
@@ -111,7 +111,8 @@ class DoubleToStringConverter {
                           int decimal_in_shortest_low,
                           int decimal_in_shortest_high,
                           int max_leading_padding_zeroes_in_precision_mode,
-                          int max_trailing_padding_zeroes_in_precision_mode)
+                          int max_trailing_padding_zeroes_in_precision_mode,
+                          int min_exponent_width = 0)
       : flags_(flags),
         infinity_symbol_(infinity_symbol),
         nan_symbol_(nan_symbol),
@@ -121,7 +122,8 @@ class DoubleToStringConverter {
         max_leading_padding_zeroes_in_precision_mode_(
             max_leading_padding_zeroes_in_precision_mode),
         max_trailing_padding_zeroes_in_precision_mode_(
-            max_trailing_padding_zeroes_in_precision_mode) {
+            max_trailing_padding_zeroes_in_precision_mode),
+        min_exponent_width_(min_exponent_width) {
     // When 'trailing zero after the point' is set, then 'trailing point'
     // must be set too.
     DOUBLE_CONVERSION_ASSERT(((flags & EMIT_TRAILING_DECIMAL_POINT) != 0) ||
@@ -378,6 +380,7 @@ class DoubleToStringConverter {
   const int decimal_in_shortest_high_;
   const int max_leading_padding_zeroes_in_precision_mode_;
   const int max_trailing_padding_zeroes_in_precision_mode_;
+  const int min_exponent_width_;
 
   DOUBLE_CONVERSION_DISALLOW_IMPLICIT_CONSTRUCTORS(DoubleToStringConverter);
 };
diff --git a/test/cctest/test-conversions.cc b/test/cctest/test-conversions.cc
index 397d8b3..0753489 100644
--- a/test/cctest/test-conversions.cc
+++ b/test/cctest/test-conversions.cc
@@ -71,6 +71,36 @@ TEST(DoubleToShortest) {
   CHECK(dc.ToShortest(-0.0, &builder));
   CHECK_EQ("0", builder.Finalize());
 
+  // Exponent min width test
+  flags = DoubleToStringConverter::UNIQUE_ZERO |
+      DoubleToStringConverter::EMIT_POSITIVE_EXPONENT_SIGN;
+  DoubleToStringConverter dcExpWidth(flags, NULL, NULL, 'e', -4, 6, 0, 0, 2);
+  builder.Reset();
+
+  builder.Reset();
+  CHECK(dcExpWidth.ToShortest(11111111111.0, &builder));
+  CHECK_EQ("1.1111111111e+10", builder.Finalize());
+
+  builder.Reset();
+  CHECK(dcExpWidth.ToShortest(1111111111.0, &builder));
+  CHECK_EQ("1.111111111e+09", builder.Finalize());
+
+  builder.Reset();
+  CHECK(dcExpWidth.ToShortest(1111111.0, &builder));
+  CHECK_EQ("1.111111e+06", builder.Finalize());
+
+  builder.Reset();
+  CHECK(dcExpWidth.ToShortest(111111.0, &builder));
+  CHECK_EQ("111111", builder.Finalize());
+
+  builder.Reset();
+  CHECK(dcExpWidth.ToShortest(10000000000.0, &builder));
+  CHECK_EQ("1e+10", builder.Finalize());
+
+  builder.Reset();
+  CHECK(dcExpWidth.ToShortest(1000000000.0, &builder));
+  CHECK_EQ("1e+09", builder.Finalize());
+
   flags = DoubleToStringConverter::NO_FLAGS;
   DoubleToStringConverter dc2(flags, NULL, NULL, 'e', -1, 1, 0, 0);
   builder.Reset();