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nlohmann · May 7, 2020 · b87b962 · b87b962
1 parent 0ae471c
commit b87b962
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Showing 3 changed files with 30 additions and 4 deletions.
diff --git a/include/nlohmann/detail/output/binary_writer.hpp b/include/nlohmann/detail/output/binary_writer.hpp
@@ -178,6 +178,7 @@ class binary_writer
             case value_t::number_float:
             {
 		double valueD = j.m_value.number_float;
+		float valueF = (float)valueD;
 		if (std::isnan(valueD)) {
 		    // NaN is 0xf97e00 in CBOR
 		    oa->write_character(to_char_type(0xF9));
@@ -189,8 +190,13 @@ class binary_writer
 		    oa->write_character(valueD > 0 ? to_char_type(0x7C) : to_char_type(0xFC));
 		    oa->write_character(to_char_type(0x00));
 		} else {
-		    oa->write_character(get_cbor_float_prefix(valueD));
-		    write_number(valueD);
+                    if((double)valueF == valueD) {
+		        oa->write_character(get_cbor_float_prefix(valueF));
+		        write_number(valueF);
+                    } else {
+		        oa->write_character(get_cbor_float_prefix(valueD));
+		        write_number(valueD);
+                    }
 		}
                 break;
             }

diff --git a/single_include/nlohmann/json.hpp b/single_include/nlohmann/json.hpp
@@ -12165,6 +12165,7 @@ class binary_writer
             case value_t::number_float:
             {
 		double valueD = j.m_value.number_float;
+		float valueF = (float)valueD;
 		if (std::isnan(valueD)) {
 		    // NaN is 0xf97e00 in CBOR
 		    oa->write_character(to_char_type(0xF9));
@@ -12176,8 +12177,13 @@ class binary_writer
 		    oa->write_character(valueD > 0 ? to_char_type(0x7C) : to_char_type(0xFC));
 		    oa->write_character(to_char_type(0x00));
 		} else {
-		    oa->write_character(get_cbor_float_prefix(valueD));
-		    write_number(valueD);
+                    if((double)valueF == valueD) {
+		        oa->write_character(get_cbor_float_prefix(valueF));
+		        write_number(valueF);
+                    } else {
+		        oa->write_character(get_cbor_float_prefix(valueD));
+		        write_number(valueD);
+                    }
 		}
                 break;
             }

diff --git a/test/src/unit-cbor.cpp b/test/src/unit-cbor.cpp
@@ -853,6 +853,20 @@ TEST_CASE("CBOR")
 
                     CHECK(json::from_cbor(result, true, false) == j);
                 }
+                SECTION("0.5")
+                {
+                    double v = 0.5;
+                    json j = v;
+                    // its double-precision float binary value is
+                    // {0xfb, 0x3f, 0xe0, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00}
+                    // but to save memory, we can store it as single-precision float.
+                    std::vector<uint8_t> expected = {0xfa, 0x3f, 0x00, 0x00, 0x00};
+                    const auto result = json::to_cbor(j);
+                    CHECK(result == expected);
+                    // roundtrip
+                    CHECK(json::from_cbor(result) == j);
+                    CHECK(json::from_cbor(result) == v);
+                }
             }
 
             SECTION("half-precision float (edge cases)")