Merge pull request #1102 from cppalliance/1100

Fix unspecified format precision being 6 digits instead of shortest representation

Author: mborland

include/boost/decimal/fmt_format.hpp

@@ -36,7 +36,7 @@ template <typename ParseContext>
 constexpr auto parse_impl(ParseContext &ctx)
 {
     auto sign_character = sign_option::minus;
-    int ctx_precision = 6;
+    int ctx_precision = -1;
     boost::decimal::chars_format fmt = boost::decimal::chars_format::general;
     bool is_upper = false;
     int padding_digits = 0;
@@ -203,7 +203,15 @@ struct formatter
             // LCOV_EXCL_STOP
         }
 
-        const auto r = boost::decimal::to_chars(buffer_front, buffer.data() + buffer.size(), v, fmt, ctx_precision);
+        boost::decimal::to_chars_result r {};
+        if (ctx_precision != -1)
+        {
+            r = boost::decimal::to_chars(buffer_front, buffer.data() + buffer.size(), v, fmt, ctx_precision);
+        }
+        else
+        {
+            r = boost::decimal::to_chars(buffer_front, buffer.data() + buffer.size(), v, fmt);
+        }
 
         std::string s(buffer.data(), static_cast<std::size_t>(r.ptr - buffer.data()));
 

include/boost/decimal/format.hpp

@@ -42,7 +42,7 @@ constexpr auto parse_impl(ParseContext &ctx)
 {
     auto sign_character = format_sign_option::minus;
     auto it {ctx.begin()};
-    int ctx_precision = 6;
+    int ctx_precision = -1;
     boost::decimal::chars_format fmt = boost::decimal::chars_format::general;
     bool is_upper = false;
     int padding_digits = 0;
@@ -207,7 +207,15 @@ struct formatter<T>
             // LCOV_EXCL_STOP
         }
 
-        const auto r = to_chars(buffer_front, buffer.data() + buffer.size(), v, fmt, ctx_precision);
+        boost::decimal::to_chars_result r {};
+        if (ctx_precision != -1)
+        {
+            r = to_chars(buffer_front, buffer.data() + buffer.size(), v, fmt, ctx_precision);
+        }
+        else
+        {
+            r = to_chars(buffer_front, buffer.data() + buffer.size(), v, fmt);
+        }
 
         std::string s(buffer.data(), static_cast<std::size_t>(r.ptr - buffer.data()));
 

test/test_format.cpp

@@ -84,9 +84,9 @@ void test_general()
 template <typename T>
 void test_fixed()
 {
-    BOOST_TEST_EQ(std::format("{:f}", T {-21, 6}), "-21000000.000000");
-    BOOST_TEST_EQ(std::format("{:f}", T {-211, 6}), "-211000000.000000");
-    BOOST_TEST_EQ(std::format("{:f}", T {-2111, 6}), "-2111000000.000000");
+    BOOST_TEST_EQ(std::format("{:f}", T {-21, 6}), "-21000000");
+    BOOST_TEST_EQ(std::format("{:f}", T {-211, 6}), "-211000000");
+    BOOST_TEST_EQ(std::format("{:f}", T {-2111, 6}), "-2111000000");
 
     BOOST_TEST_EQ(std::format("{:.0f}", T {-21, 6}), std::string{"-21000000"});
     BOOST_TEST_EQ(std::format("{:.0f}", T {-211, 6}), std::string{"-211000000"});
@@ -115,13 +115,13 @@ void test_fixed()
 template <typename T>
 void test_scientific()
 {
-    BOOST_TEST_EQ(std::format("{:e}", T {-21, 6}), "-2.100000e+07");
-    BOOST_TEST_EQ(std::format("{:e}", T {-211, 6}), "-2.110000e+08");
-    BOOST_TEST_EQ(std::format("{:e}", T {-2111, 6}), "-2.111000e+09");
+    BOOST_TEST_EQ(std::format("{:e}", T {-21, 6}), "-2.1e+07");
+    BOOST_TEST_EQ(std::format("{:e}", T {-211, 6}), "-2.11e+08");
+    BOOST_TEST_EQ(std::format("{:e}", T {-2111, 6}), "-2.111e+09");
 
-    BOOST_TEST_EQ(std::format("{:E}", T {-21, 6}), "-2.100000E+07");
-    BOOST_TEST_EQ(std::format("{:E}", T {-211, 6}), "-2.110000E+08");
-    BOOST_TEST_EQ(std::format("{:E}", T {-2111, 6}), "-2.111000E+09");
+    BOOST_TEST_EQ(std::format("{:E}", T {-21, 6}), "-2.1E+07");
+    BOOST_TEST_EQ(std::format("{:E}", T {-211, 6}), "-2.11E+08");
+    BOOST_TEST_EQ(std::format("{:E}", T {-2111, 6}), "-2.111E+09");
 
     BOOST_TEST_EQ(std::format("{:.0E}", T {0}), "0E+00");
     BOOST_TEST_EQ(std::format("{:e}", std::numeric_limits<T>::infinity()), "inf");

test/test_format_fmtlib.cpp

@@ -130,9 +130,9 @@ void test_general()
 template <typename T>
 void test_fixed()
 {
-    BOOST_TEST_EQ(fmt::format("{:f}", T {21u, 6, true}), "-21000000.000000");
-    BOOST_TEST_EQ(fmt::format("{:f}", T {211u, 6, true}), "-211000000.000000");
-    BOOST_TEST_EQ(fmt::format("{:f}", T {2111u, 6, true}), "-2111000000.000000");
+    BOOST_TEST_EQ(fmt::format("{:f}", T {21u, 6, true}), "-21000000");
+    BOOST_TEST_EQ(fmt::format("{:f}", T {211u, 6, true}), "-211000000");
+    BOOST_TEST_EQ(fmt::format("{:f}", T {2111u, 6, true}), "-2111000000");
 
     BOOST_TEST_EQ(fmt::format("{:.0f}", T {21u, 6, true}), std::string{"-21000000"});
     BOOST_TEST_EQ(fmt::format("{:.0f}", T {211u, 6, true}), std::string{"-211000000"});
@@ -161,13 +161,13 @@ void test_fixed()
 template <typename T>
 void test_scientific()
 {
-    BOOST_TEST_EQ(fmt::format("{:e}", T {21u, 6, true}), "-2.100000e+07");
-    BOOST_TEST_EQ(fmt::format("{:e}", T {211u, 6, true}), "-2.110000e+08");
-    BOOST_TEST_EQ(fmt::format("{:e}", T {2111u, 6, true}), "-2.111000e+09");
+    BOOST_TEST_EQ(fmt::format("{:e}", T {21u, 6, true}), "-2.1e+07");
+    BOOST_TEST_EQ(fmt::format("{:e}", T {211u, 6, true}), "-2.11e+08");
+    BOOST_TEST_EQ(fmt::format("{:e}", T {2111u, 6, true}), "-2.111e+09");
 
-    BOOST_TEST_EQ(fmt::format("{:E}", T {21u, 6, true}), "-2.100000E+07");
-    BOOST_TEST_EQ(fmt::format("{:E}", T {211u, 6, true}), "-2.110000E+08");
-    BOOST_TEST_EQ(fmt::format("{:E}", T {2111u, 6, true}), "-2.111000E+09");
+    BOOST_TEST_EQ(fmt::format("{:E}", T {21u, 6, true}), "-2.1E+07");
+    BOOST_TEST_EQ(fmt::format("{:E}", T {211u, 6, true}), "-2.11E+08");
+    BOOST_TEST_EQ(fmt::format("{:E}", T {2111u, 6, true}), "-2.111E+09");
 
     BOOST_TEST_EQ(fmt::format("{:.0E}", T {0}), "0E+00");
     BOOST_TEST_EQ(fmt::format("{:e}", std::numeric_limits<T>::infinity()), "inf");