Error running [RC] Arbitrary Size Bit Adder - ByRef Issue?

[Brandon Parker]

The Arbitrary Size Bit Adder code shown below should all show an overflow, but it does not. The code runs normally under LB 4.5.1. The bit string appears to be formatted correctly, but something is going awry with the carryOut variable. Maybe because each function uses the same named ByRef carryOut variable?

' 0110
' 1110
'=0100 with Overflow
Print arbitrarySizeBitAdder$(8, "0110", "1110", Overflow);", Overflow: ";Overflow
Print arbitrarySizeBitAdder$(8, "10010011", "11111111", Overflow);", Overflow: ";Overflow
Print arbitrarySizeBitAdder2$(8, "10010011", "11111111", Overflow);", Overflow: ";Overflow

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   Function xorGate(a, b)
       xorGate = ((a And Not(b)) Or (Not(a) And b))
   End Function

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   Function halfAdder(a, b, ByRef carryOut)
       carryOut = 0
       halfAdder = xorGate(a, b)
       carryOut = (a And b)
   End Function

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   Function fullAdderFromHalfAdder(a, b, carryIn, ByRef carryOut)
       fullAdderFromHalfAdder = halfAdder(halfAdder(carryIn, a, carryOutA), b, carryOutB)
       carryOut = (carryOutA Or carryOutB)
   End Function

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   Function fullAdder(a, b, carryIn, ByRef carryOut)
       carryOut = 0
       xorAB = xorGate(a, b)
       fullAdder = xorGate(xorAB, carryIn)
       carryOut = ((xorAB And carryIn) Or (a And b))
   End Function

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   Function arbitrarySizeBitAdder$(bitCount, bitSet1$, bitSet2$, ByRef vBit)
       vBit = 0
       bitSet1$ = Right$(string$("0", bitCount);bitSet1$, bitCount)
       bitSet2$ = Right$(string$("0", bitCount);bitSet2$, bitCount)

       For i = bitCount To 1 Step -1
           arbitrarySizeBitAdder$ = fullAdderFromHalfAdder(Val(Mid$(bitSet1$, i, 1)), Val(Mid$(bitSet2$, i, 1)), vBit, vBit);arbitrarySizeBitAdder$
       Next i
   End Function

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   Function arbitrarySizeBitAdder2$(bitCount, bitSet1$, bitSet2$, ByRef vBit)
       vBit = 0
       bitSet1$ = Right$(string$("0", bitCount);bitSet1$, bitCount)
       bitSet2$ = Right$(string$("0", bitCount);bitSet2$, bitCount)

       For i = bitCount To 1 Step -1
           arbitrarySizeBitAdder2$ = fullAdder(Val(Mid$(bitSet1$, i, 1)), Val(Mid$(bitSet2$, i, 1)), vBit, vBit);arbitrarySizeBitAdder2$
       Next i
   End Function

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   Function string$(myString$, numstring)
       For i = 1 To numstring
           string$ = string$ + myString$
       Next i
   End Function

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Hardware: Samsung Laptop Intel Core i7, 16GB of RAM
Operating System: Windows 10 Home build 18363.1016 - 64-bit


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Brandon Parker

[Carl Gundel]

Mar 31, 2021 17:38:52 GMT -5 Brandon Parker said:

The Arbitrary Size Bit Adder code shown below should all show an overflow, but it does not. The code runs normally under LB 4.5.1. The bit string appears to be formatted correctly, but something is going awry with the carryOut variable. Maybe because each function uses the same named ByRef carryOut variable?

There needs to be a little more robustness in the way that parameters are passed.  Partly there is bugginess when the same variable is passed more than once in the same call, and also the compiler needs to throw an error when it sees code pass the same variable into more than one byref slot (your code isn't doing that).  And, there may be something else.  Working on it.