Fix signed compare of byte string.

TPMCmd/tpm/src/support/MathOnByteBuffers.c

@@ -70,6 +70,7 @@ UnsignedCompareB(
                 return (a[i] > b[i]) ? 1 : -1;
         }
     }
+    // Will return == if sizes are both zero
     return 0;
 }
 
@@ -87,26 +88,13 @@ SignedCompareB(
     const BYTE      *b              // IN: b buffer
     )
 {
-    int      signA, signB;       // sign of a and b
-
-    // For positive or 0, sign_a is 1
-    // for negative, sign_a is 0
-    signA = ((a[0] & 0x80) == 0) ? 1 : 0;
-
-    // For positive or 0, sign_b is 1
-    // for negative, sign_b is 0
-    signB = ((b[0] & 0x80) == 0) ? 1 : 0;
-
-    if(signA != signB)
-    {
-        return signA - signB;
-    }
-    if(signA == 1)
-        // do unsigned compare function
-        return UnsignedCompareB(aSize, a, bSize, b);
+    // are the signs different ?
+    if(((a[0] ^ b[0]) & 0x80) > 0)
+        // if the signs are different, then a is less than b if a is negative.
+        return a[0] & 0x80 ? -1 : 1;
     else
-        // do unsigned compare the other way
-        return 0 - UnsignedCompareB(aSize, a, bSize, b);
+    // do unsigned compare function
+        return UnsignedCompareB(aSize, a, bSize, b);
 }
 
 //*** ModExpB
@@ -203,9 +191,9 @@ DivideB(
 }
 
 //*** AdjustNumberB()
-// Remove/add leading zeros from a number in a TPM2B. Will try to make the number 
-// by adding or removing leading zeros. If the number is larger than the requested 
-// size, it will make the number as small as possible. Setting 'requestedSize' to 
+// Remove/add leading zeros from a number in a TPM2B. Will try to make the number
+// by adding or removing leading zeros. If the number is larger than the requested
+// size, it will make the number as small as possible. Setting 'requestedSize' to
 // zero is equivalent to requesting that the number be normalized.
 UINT16
 AdjustNumberB(
@@ -233,7 +221,7 @@ AdjustNumberB(
         }
     }
     // This is a request to shift the number to the right (add leading zeros)
-    else 
+    else
     {
         MemoryCopy(&num->buffer[requestedSize - num->size], num->buffer, num->size);
         MemorySet(num->buffer, 0, requestedSize- num->size);
@@ -243,7 +231,7 @@ AdjustNumberB(
 }
 
 //*** ShiftLeft()
-// This function shifts a byte buffer (a TPM2B) one byte to the left. That is, 
+// This function shifts a byte buffer (a TPM2B) one byte to the left. That is,
 // the most significant bit of the most significant byte is lost.
 TPM2B *
 ShiftLeft(