Fix exponent validation

References #25
Lawo · May 23, 2016 · 1d3310f · 1d3310f
1 parent 47c89d1
commit 1d3310f
Show file tree

Hide file tree

Showing 2 changed files with 14 additions and 14 deletions.
diff --git a/Lawo.EmberPlusSharp/Ember/EmberReader.cs b/Lawo.EmberPlusSharp/Ember/EmberReader.cs
@@ -466,7 +466,7 @@ private static double ReadReal(ReadBuffer readBuffer, int length)
 
             var firstContentsOctet = readBuffer[readBuffer.Index++];
             --length;
-            long sign;
+            long signBits;
             int exponentLength;
 
             // 8.5.3 - 8.5.7, encoding must be base 2, so the bits 6 to 3 must be 0. Moreover, bits 8 to 7 must not
@@ -484,42 +484,42 @@ private static double ReadReal(ReadBuffer readBuffer, int length)
 
                 // 8.5.7.4 a)
                 case 0x80:
-                    sign = 0;
+                    signBits = 0;
                     exponentLength = 1;
                     break;
                 case 0xC0:
-                    sign = long.MinValue;
+                    signBits = long.MinValue;
                     exponentLength = 1;
                     break;
 
                 // 8.5.7.4 b)
                 case 0x81:
-                    sign = 0;
+                    signBits = 0;
                     exponentLength = 2;
                     break;
                 case 0xC1:
-                    sign = long.MinValue;
+                    signBits = long.MinValue;
                     exponentLength = 2;
                     break;
 
                 // 8.5.7.4 c)
                 case 0x82:
-                    sign = 0;
+                    signBits = 0;
                     exponentLength = 3;
                     break;
                 case 0xC2:
-                    sign = long.MinValue;
+                    signBits = long.MinValue;
                     exponentLength = 3;
                     break;
 
                 // 8.5.7.4 d)
                 case 0x83:
-                    sign = 0;
+                    signBits = 0;
                     exponentLength = readBuffer[readBuffer.Index++];
                     --length;
                     break;
                 case 0xC3:
-                    sign = long.MinValue;
+                    signBits = long.MinValue;
                     exponentLength = readBuffer[readBuffer.Index++];
                     --length;
                     break;
@@ -538,14 +538,13 @@ private static double ReadReal(ReadBuffer readBuffer, int length)
 
             var exponent = Read8Bit(readBuffer, exponentLength, true);
 
-            if ((exponent < -Constants.DoubleExponentBias) || (exponent > Constants.DoubleExponentBias))
+            // https://en.wikipedia.org/wiki/Double-precision_floating-point_format
+            if ((exponent <= -Constants.DoubleExponentBias) || (exponent > Constants.DoubleExponentBias))
             {
                 throw CreateEmberException(
                     "The exponent of the Real at position {0} exceeds the expected range.", position);
             }
 
-            exponent = (exponent + Constants.DoubleExponentBias) << Constants.DoubleMantissaBits;
-
             var mantissa = Read8Bit(readBuffer, mantissaLength, false);
 
             if (mantissa == 0)
@@ -567,7 +566,8 @@ private static double ReadReal(ReadBuffer readBuffer, int length)
             }
 
             mantissa &= Constants.DoubleMantissaMask;
-            return BitConverter.Int64BitsToDouble(sign | exponent | mantissa);
+            var exponentBits = (exponent + Constants.DoubleExponentBias) << Constants.DoubleMantissaBits;
+            return BitConverter.Int64BitsToDouble(signBits | exponentBits | mantissa);
         }
 
         /// <summary>See <i>"X.690"</i><cite>X.690</cite>, chapter 8.1.3.</summary>

diff --git a/Lawo.EmberPlusSharpTest/Ember/EmberReaderTest.cs b/Lawo.EmberPlusSharpTest/Ember/EmberReaderTest.cs
@@ -250,7 +250,7 @@ public void ExceptionTest()
 
             AssertEmberException(
                 "The exponent of the Real at position 4 exceeds the expected range.",
-                0x60, 0x06, 0x09, 0x04, 0x81, 0xFC, 0x00, 0x01);
+                0x60, 0x06, 0x09, 0x04, 0x81, 0xFC, 0x01, 0x01);
 
             AssertEmberException(
                 "The mantissa of the Real at position 4 is zero.", 0x60, 0x05, 0x09, 0x03, 0x80, 0x00, 0x00);