Q65323: BASIC Program to Read COBOL BCD (COMP-3) Numbers
Article: Q65323
Product(s): See article
Version(s): 6.00 6.00b 7.00 7.10 | 6.00 6.00b 7.00 7.10
Operating System(s): MS-DOS | OS/2
Keyword(s): ENDUSER | SR# S900828-36 B_COBOL | mspl13_basic
Last Modified: 2-JAN-1991
Below is a BASIC program that reads a data file created by Microsoft
COBOL containing binary-coded-decimal (COMP-3) numbers. This is
accomplished by reading in the file one byte at a time, interpreting
those bytes according to the binary-coded-decimal (BCD) format, and
performing calculations based on those interpretations to generate
equivalent BASIC double-precision floating-point numbers.
This information applies to Microsoft QuickBASIC versions 4.00, 4.00b,
and 4.50 for MS-DOS; to Microsoft BASIC Compiler versions 6.00 and
6.00b for MS-DOS and MS OS/2; and to Microsoft BASIC Professional
Development System (PDS) versions 7.00 and 7.10 for MS-DOS and MS
OS/2.
The information about binary-coded-decimal numbers and the COMP-3
format applies to Microsoft COBOL Compiler versions 3.00 and 3.00a for
MS-DOS and MS OS/2, and to Microsoft COBOL Professional Development
System version 4.00 for MS-DOS and MS OS/2.
Microsoft COBOL 3.00, 3.00a, and 4.00 support a data type commonly
referred to as binary-coded-decimal (BCD) format. The syntactical name
for this data type in COBOL is COMP-3.
The bytes used to store a COMP-3 number can contain two base-10 digits
each. The high nibble (4 bits) stores one digit of the number and the
low nibble (4 bits) stores the next digit to the right. That is, the
high nibble stores a digit whose place in the number has a power of 10
that is one greater than that of the digit in the low nibble.
Moreover, the first byte used to store the number will contain the
digit with the highest power of 10; subsequent bytes will hold digits
that have successively lesser powers of 10. (Note: There are two
nibbles in every byte.)
A special case is made for the last byte, where the high nibble stores
the last digit in the number, and the low nibble stores the sign of
the number. The low nibble will contain 15 if the number is unsigned,
12 for positive, and 13 for negative. Also, if the number of nibbles
needed for digits plus the sign nibble will not fill a whole number of
bytes, the high nibble of the byte storing the first digit is set to
0.
As an example, here is a binary representation of how the number 69
(signed positive) would be stored:
+---------- First Byte ---------+--------- Second Byte ---------+
| | |
+- High Nibble -+- Low Nibble --+- High Nibble -+- Low Nibble --+
| | | | |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| 0 | 0 | 0 | 0 | 0 | 1 | 1 | 0 | 1 | 0 | 0 | 1 | 1 | 1 | 0 | 0 |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| | | | |
+------ 0 ------+------ 6 ------+------ 9 ------+-- Positive ---+
Below is a BASIC program (BCDTODBL.BAS) that converts the COMP-3
numbers in a COBOL data file to BASIC's double-precision numbers. The
program reads in each byte of the file sequentially, interpreting it
as either a pair of digits or a digit and a sign. The program knows
that it has read all the digits in a number when the low nibble of the
last byte read contains a sign value (12, 13, or 15). When this
happens, the program circulates through all the digits accumulated for
the number and multiplies each by its associated power of 10. The
result of this iterative calculation is assigned to a double-precision
floating-point number. Finally, one more calculation is performed on
the number so that it will contain the amount of decimal places
specified by the user.
Following the BASIC program is a COBOL program (WRITEBCD.CBL) that
creates a file containing a user-specified amount of COMP-3 signed
numbers. To compile and link the program in COBOL 3.00 or 3.00a, enter
the following commands from the DOS or OS/2 prompt:
cobol writebcd;
link writebcd;
The compile lines for COBOL Professional Development System (PDS)
version 4.00 are as follows:
cobol writebcd;
link writebcd,,,coblib cobapi;
The BASIC program can be run or compiled from within the QB.EXE or
QBX.EXE environments. See your BASIC documentation for information on
using the QB.EXE or QBX.EXE environments.
BCDTODBL.BAS
------------
DIM Digits%(15) 'Holds the digits for each number (max = 16).
DIM BASICeqv#(1000) 'Holds the BASIC equivalent of each COMP-3 number.
'Clear the screen, get the filename and the amount of decimal places
'desired for each number, and open the file for sequential input:
CLS
INPUT "Enter the COBOL data file name: ", FileName$
INPUT "Enter the number of decimal places desired: ", Decimal%
OPEN FileName$ FOR INPUT AS #1
DO UNTIL EOF(1) 'Loop until the end of the file is reached.
Byte$ = INPUT$(1, 1) 'Read in a byte.
IF Byte$ = CHR$(0) THEN 'Check if byte is 0 (ASC won't work on 0).
Digits%(HighPower%) = 0 'Make next two digits 0. Increment
Digits%(HighPower% + 1) = 0 'the high power to reflect the
HighPower% = HighPower% + 2 'number of digits in the number
'plus 1.
ELSE
HighNibble% = ASC(Byte$) \ 16 'Extract the high and low
LowNibble% = ASC(Byte$) AND &HF 'nibbles from the byte. The
Digits%(HighPower%) = HighNibble% 'high nibble will always be a
'digit.
IF LowNibble% <= 9 THEN 'If low nibble is a
'digit, assign it and
Digits%(HighPower% + 1) = LowNibble% 'increment the high
HighPower% = HighPower% + 2 'power accordingly.
ELSE
HighPower% = HighPower% + 1 'Low nibble was not a digit but a
Digit% = 0 '+ or - signals end of number.
'Start at the highest power of 10 for the number and multiply
'each digit by the power of 10 place it occupies.
FOR Power% = (HighPower% - 1) TO 0 STEP -1
BASICeqv#(E%)=BASICeqv#(E%) + (Digits%(Digit%) * (10^Power%))
Digit% = Digit% + 1
NEXT
'If the sign read was negative, make the number negative.
IF LowNibble% = 13 THEN
BASICeqv#(E%) = BASICeqv#(E%) - (2 * BASICeqv#(E%))
END IF
'Give the number the desired amount of decimal places, print
'the number, increment E% to point to the next number to be
'converted, and reinitialize the highest power.
BASICeqv#(E%) = BASICeqv#(E%) / (10 ^ Decimal%)
PRINT BASICeqv#(E%)
E% = E% + 1
HighPower% = 0
END IF
END IF
LOOP
CLOSE 'Close the COBOL data file, and end.
WRITEBCD.CBL
------------
$SET ANS85
IDENTIFICATION DIVISION.
PROGRAM-ID. WriteBCD.
ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION.
FILE-CONTROL.
SELECT BCDFile ASSIGN TO "BCD.DAT".
DATA DIVISION.
FILE SECTION.
FD BCDFile.
01 BCDNumber PIC S9(5) COMP-3.
WORKING-STORAGE SECTION.
* Holds the number of COMP-3 items to write to the file.
01 TotalNumbers PIC 99 COMP-5.
PROCEDURE DIVISION.
* Get the number of COMP-3 items to write to file.
DISPLAY "Enter the number of items to write:".
ACCEPT TotalNumbers.
* Open the COMP-3 file for sequential output and write each
* number out to the file as the user enters it.
OPEN OUTPUT BCDFile.
PERFORM TotalNumbers TIMES
ACCEPT BCDNumber
WRITE BCDNumber
END-PERFORM.
* Close the COMP-3 file and end.
CLOSE BCDFile.
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