From 40414b34468046ed84eb2897682d49964986c467 Mon Sep 17 00:00:00 2001
From: Victor Zverovich <victor.zverovich@gmail.com>
Date: Mon, 28 Oct 2019 12:31:00 -0700
Subject: [PATCH] Don't emit trailing zeros in exponential notation (#1376)

---
 include/fmt/format-inl.h | 10 +++++++++-
 include/fmt/format.h     |  4 ----
 test/printf-test.cc      |  4 ++--
 3 files changed, 11 insertions(+), 7 deletions(-)

diff --git a/include/fmt/format-inl.h b/include/fmt/format-inl.h
index d6ecc366..b412b928 100644
--- a/include/fmt/format-inl.h
+++ b/include/fmt/format-inl.h
@@ -1070,7 +1070,15 @@ bool grisu_format(Double value, buffer<char>& buf, int precision,
     fixed_handler handler{buf.data(), 0, precision, -cached_exp10, fixed};
     if (grisu_gen_digits(normalized, 1, exp, handler) == digits::error)
       return false;
-    buf.resize(to_unsigned(handler.size));
+    int num_digits = handler.size;
+    if (!fixed) {
+      // Remove trailing zeros.
+      while (num_digits > 0 && buf[num_digits - 1] == '0') {
+        --num_digits;
+        ++exp;
+      }
+    }
+    buf.resize(to_unsigned(num_digits));
   } else {
     fp fp_value;
     fp lower, upper;  // w^- and w^+ in the Grisu paper.
diff --git a/include/fmt/format.h b/include/fmt/format.h
index e665d612..41f9cc01 100644
--- a/include/fmt/format.h
+++ b/include/fmt/format.h
@@ -1073,10 +1073,6 @@ template <typename Char> class grisu_writer {
       *it++ = static_cast<Char>(*digits_);
       if (num_digits_ > 1) *it++ = decimal_point_;
       it = copy_str<Char>(digits_ + 1, digits_ + num_digits_, it);
-      if (num_digits_ < params_.num_digits) {
-        it = std::fill_n(it, params_.num_digits - num_digits_,
-                         static_cast<Char>('0'));
-      }
       *it++ = static_cast<Char>(params_.upper ? 'E' : 'e');
       return write_exponent<Char>(full_exp - 1, it);
     }
diff --git a/test/printf-test.cc b/test/printf-test.cc
index d8fbc964..75101226 100644
--- a/test/printf-test.cc
+++ b/test/printf-test.cc
@@ -410,6 +410,7 @@ TEST(PrintfTest, Float) {
   EXPECT_PRINTF("392.65", "%G", 392.65);
   EXPECT_PRINTF("392", "%g", 392.0);
   EXPECT_PRINTF("392", "%G", 392.0);
+  EXPECT_PRINTF("4.56e-07", "%g", 0.000000456);
   safe_sprintf(buffer, "%a", -392.65);
   EXPECT_EQ(buffer, format("{:a}", -392.65));
   safe_sprintf(buffer, "%A", -392.65);
@@ -588,8 +589,7 @@ class custom_printf_arg_formatter : public formatter_t {
       if (round(value * pow(10, specs()->precision)) == 0.0) value = 0;
   return formatter_t::operator()(value);
 }
-}
-;
+};
 
 typedef fmt::basic_format_args<context_t> format_args_t;