fix serialization of some floating-point values

CBOR/PeterO/Cbor/CBORObject.cs

@@ -6309,7 +6309,9 @@ public static int WriteFloatingPointBits(
           }
         } else if (byteCount == 4) {
           int bits =
-            CBORUtilities.SingleToHalfPrecisionIfSameValue(floatingBits);
+
+            CBORUtilities.SingleToHalfPrecisionIfSameValue(
+              unchecked((int)floatingBits));
           if (bits != -1) {
             return WriteFloatingPointBits(outputStream, bits, 2, false);
           }

CBOR/PeterO/Cbor/CBORUtilities.cs

@@ -1627,8 +1627,7 @@ public static int DoubleToRoundedSinglePrecision(long bits) {
       }
     }
 
-    public static int SingleToHalfPrecisionIfSameValue(float f) {
-      int bits = BitConverter.ToInt32(BitConverter.GetBytes((float)f), 0);
+    public static int SingleToHalfPrecisionIfSameValue(int bits) {
       int exp = (bits >> 23) & 0xff;
       int mant = bits & 0x7fffff;
       int sign = (bits >> 16) & 0x8000;

CBORTest/CBORObjectTest.cs

@@ -6878,6 +6878,49 @@ public static void TestWriteExtraOne(long longValue) {
       }
     }
 
+    private void TestWriteUnchangedFloatBits(int bits) {
+          using (var ms = new Test.DelayingStream()) {
+            byte[] expectedBytes = {
+              (byte)0xfa,
+              (byte)((bits >> 24) & 0xff),
+              (byte)((bits >> 16) & 0xff),
+              (byte)((bits >> 8) & 0xff),
+              (byte)(bits & 0xff)
+            };
+            CBORObject.WriteFloatingPointBits(ms, bits, 4, true);
+            TestCommon.AssertByteArraysEqual(expectedBytes, ms.ToArray());
+          }
+    }
+
+    private void TestWriteUnchangedDoubleBits(long bits) {
+          using (var ms = new Test.DelayingStream()) {
+            byte[] expectedBytes = {
+              (byte)0xfb,
+              (byte)((bits >> 56) & 0xffL),
+              (byte)((bits >> 48) & 0xffL),
+              (byte)((bits >> 40) & 0xffL),
+              (byte)((bits >> 32) & 0xffL),
+              (byte)((bits >> 24) & 0xffL),
+              (byte)((bits >> 16) & 0xffL),
+              (byte)((bits >> 8) & 0xffL),
+              (byte)(bits & 0xffL)
+            };
+            CBORObject.WriteFloatingPointBits(ms, bits, 8, true);
+            TestCommon.AssertByteArraysEqual(expectedBytes, ms.ToArray());
+          }
+    }
+
+    [Test]
+    public void TestWriteSubnormalFloat() {
+      for (var i = 1; i <= 0x1fff; ++i) {
+          this.TestWriteUnchangedFloatBits(i);
+          this.TestWriteUnchangedFloatBits(0x2000 + i);
+          this.TestWriteUnchangedFloatBits(0x4000 + i);
+          this.TestWriteUnchangedFloatBits(0x8000 + i);
+          this.TestWriteUnchangedDoubleBits((long)i);
+      }
+    }
+
     [Test]
     public void TestWriteExtra() {
       try {

CBORTest/CBORTest.csproj

@@ -1,6 +1,6 @@
 <Project Sdk='Microsoft.NET.Sdk'>
   <PropertyGroup>
-    <TargetFramework>netcoreapp8.0</TargetFramework>
+    <TargetFramework>netcoreapp7.0</TargetFramework>
   </PropertyGroup>
   <PropertyGroup Condition=' &apos;$(Configuration)&apos;==&apos;Debug&apos; '>
     <DebugType>full</DebugType>