═══ 1. BCD Calculator Overview ═══

The BCD Calculator is a simple four-function desktop calculator that is 
intended to demonstrate the facilities and functions of the BCD Class object. 

The calculator resembles other Windows and PM Calculators with a keypad and 
standard arithmetic function keys.  The big difference is that it operates on 
integers of up to 32 decimal digits in length. 

Since this version does not have floating point, you probably wouldn't want to 
replace your favorate desktop calculator.  Besides, I can't imagine anyone 
needing 32 digit arithmetic to balance their checkbook, even in countries with 
currencies that have very small unit values. 


═══ 1.1. Registers ═══

Three registers are displayed at the top of the calculator: 

o Memory 
o Accumulator 
o Entry 

The registers are more or less conventional except that all three are 
displayed.  The Memory register is set from the Accumulator and Memory Recall 
returns it's data to the Entry register.  The Accumulator is set as a result of 
some process on data from the Entry register. 

             ┌──────────Sh Right Cpld───────────┐
             │  ┌───────────┐     ┌──────────┐  │  ┌──────────┐
             └─>┤           │     │          ├──┘  │          │
      KeyPad───>┤   Entry   ├────>┤  Accum   ├────>┤  Memory  ├──┐
            ┌──>┤           │     │          │     │          │  │
            │   └───────────┘     └──────────┘     └──────────┘  │
            └───────────────Memory Recall────────────────────────┘

The Entry register is set from the keyboard, from a memory recall, or from the 
low-order digits from the accumulator on a Shift Right-Coupled operation. The 
Entry register has a "constant" capability such that its contents will be 
retained after an arithmetic function key is pressed so that you can add, 
(e.g.), the same value to the Accumulator multiple times.  The Entry register 
will clear after the += key is pressed or if a numeric key is pressed signaling 
the entry of a new value. 

The registers are read only and cannot be set from the keyboard.  However, you 
can mark a register and capture it's contents on the clipboard with a 
Ctrl-Insert. 


═══ 1.2. Shift Function Keys ═══

Directly below the registers are four shift function keys.  These are not 
particularly useful on a desktop calculator and are intended to demonstrate the 
shift functions available in the BCD Class.  The keys are: 

Key            Description 

<<n            Shift Accum left n places.  The contents of the Accumulator are 
               shifted left by the amount specified in the Entry register.  The 
               BCD Class will not allow significant digits to be shifted out of 
               the Accumulator to the left. 

>>n            Shift Accum right n places.  The contents of the Accumulator are 
               shifted right by the amount specified in the Entry register. 
               Unlike shift left, the BCD Class will allow you to shift right 
               up to 32 digits regardless of the contents of the Accumulator. 

>>n, Rnd       Shift Accum right n places and round.  Five is added to the nth 
               position before it is shifted out of the Accum.  If the nth 
               digit was >= 5, the result in the Accum is increased by one. 

>>n, Cpld      Shift Accum right n places and place the shifted digits into a 
               "coupled" register.  For the purposes of this demo, I am using 
               the Entry register to keep the digits shifted out of the 
               Accumulator.  The same result can be obtained by doing a modulus 
               to get the right-most digits and a divide to get the left. 
               Shift Right Coupled on the other hand, produces both results in 
               a single operation without using the divide algorithm and is 
               therefore much faster. 


═══ 1.3. Conventional Keys ═══

The keys below the shift functions are a set of conventional calculator keys: 

o Numeric key pad. 
o Delete key which removes the last digit entered. 
o Arithmetic function keys. 
o A += key which clears the Entry register after adding it's contents to the 
  Accumulator. 
o The Memory +,-,Clear and Recall keys. 
o Clear/Clear Entry keys. 


═══ 1.4. For Further Information ═══

For further information on the BCD Class please contact: 

Bill Connors 
JBC Enterprises, Inc. 
(301)330-8223 
CompuServe: 73124,1260