Re: Did I write a good (efficient) program?
- From: Robert <no@xxxxxx>
- Date: Sun, 30 Mar 2008 18:44:48 -0600
On Sun, 30 Mar 2008 06:37:28 -0700 (PDT), MikeB <MPBrede@xxxxxxxxx> wrote:
I haven't written COBOL in a number of years and am quite rusty.
Recently someone asked my help to write some code to display an IP V6
address in human-readable code. I wrote something, but am not sure if
I used the best available techniques. Please have a look at what I
wrote and feel free to comment.
Background. An IP V6 address is 4 words (128-bit) long. It is in
binary format. For human-readable purposes it is converted into 8
"octets" separated by colons. leading zeroes in each field are
suppressed. To compact the address, one or more adjacent octets
containing all zeroes can be compressed *once* per IP address by
simply producing a pair of colons.
thus: 76DF:54AE:A30:1:1:4321:EAD5:AA43
or FD05::1:0:5 (in this instance 4 octets have been suppressed)
or even: ::1 (loopback address)
I was under a little time pressure (only had yesterday morning), so I
haven't figured out the compression part yet. However, that is
optional, so I'll do it when I have some spare time. In the meantime,
I'd like to hear from members of this group if I could have written
cleaner, leaner and more efficient COBOL.
Efficient is Cobolese for fast. In the Good Old Days we had to hold the machine's hand,
showing it how to go fast. Concern for speed became THE criteria driving design. As
machines got faster, we kept doing it out of habit and because no one told us to stop. We
now program as though the year is still 1973, ignoring the fact that the Pentium 4 on our
desktop is 2,000 times the speed of a 370/158.
http://freespace.virgin.net/roy.longbottom/whetstone.htm
000300 IDENTIFICATION
DIVISION.
000400 PROGRAM-ID.
IPDISP.
003200 ENVIRONMENT
DIVISION.
003300 DATA
DIVISION.
003400 WORKING-STORAGE
SECTION.
007212*
IPV6
007213 01 HEX-
VALUES.
007214 05 FILLER PIC X(32) VALUE
"000102030405060708090A0B0C0D0E0F".
007215 05 FILLER PIC X(32) VALUE
"101112131415161718191A1B1C1D1E1F".
007216 05 FILLER PIC X(32) VALUE
"202122232425262728292A2B2C2D2E2F".
007217 05 FILLER PIC X(32) VALUE
"303132333435363738393A3B3C3D3E3F".
007218 05 FILLER PIC X(32) VALUE
"404142434445464748494A4B4C4D4E4F".
007219 05 FILLER PIC X(32) VALUE
"505152535455565758595A5B5C5D5E5F".
007220 05 FILLER PIC X(32) VALUE
"606162636465666768696A6B6C6D6E6F".
007221 05 FILLER PIC X(32) VALUE
"707172737475767778797A7B7C7D7E7F".
007222 05 FILLER PIC X(32) VALUE
"808182838485868788898A8B8C8D8E8F".
007223 05 FILLER PIC X(32) VALUE
"909192939495969798999A9B9C9D9E9F".
007224 05 FILLER PIC X(32) VALUE
"A0A1A2A3A4A5A6A7A8A9AAABACADAEAF".
007225 05 FILLER PIC X(32) VALUE
"B0B1B2B3B4B5B6B7B8B9BABBBCBDBEBF".
007226 05 FILLER PIC X(32) VALUE
"C0C1C2C3C4C5C6C7C8C9CACBCCCDCECF".
007227 05 FILLER PIC X(32) VALUE
"D0D1D2D3D4D5D6D7D8D9DADBDCDDDEDF".
007228 05 FILLER PIC X(32) VALUE
"E0E1E2E3E4E5E6E7E8E9EAEBECEDEEEF".
007229 05 FILLER PIC X(32) VALUE
"F0F1F2F3F4F5F6F7F8F9FAFBFCFDFEFF".
007230 01 HEX-TABLE REDEFINES HEX-
VALUES.
007231 05 HEX-BYTE PIC XX OCCURS 256
TIMES.
The table is awkward and repetitive. All you need is a single copy of the hex alphabet:
01 hex-alphabet value '0123456789ABCDEF' pic x(16).
007232
007235 01 IP-
ADDRESS.
007236 05 IP-ONE PIC
X(8).
007237 05 IP-TWO PIC
X(8).
007238 01 IP-BYTES REDEFINES IP-
ADDRESS.
007239 05 IP-BYTE6 PIC X OCCURS 16
TIMES.
007240
007241 01 IP-
BINARY.
007242 05 IP-HEX OCCURS 16
TIMES.
007243 10 FILLER PIC X VALUE LOW-
VALUES.
007244 10 IP-NUMBER-BINARY PIC
X.
007245 01 IP-INDEX REDEFINES IP-
BINARY.
007246 05 IP-NUMBER-INDEX PIC 99 USAGE COMP-5 OCCURS 16
TIMES.
Replace all that verbosity with:
01 IP-bytes redefines IP-addesses.
05 IP-binary occurs 16 binary pic 99.
01 left-nybble binary pic 99.
01 right-nybble binary pic 99.
perform varying IP-index1 from 1 by 1 until IP-index1 > 16
divide 16 into IP-binary (IP-index1)
giving left-nybble remainder right-nybble
compute IP-index2 = IP-index1 * 2
move hex-alphabet (left-nybble + 1: 1) to IP-display-byte (IP-index-2: 1)
move hex-alphabet (right-nybble + 1:1) to IP-display-byte (IP-index-2 + 1: 1)
end-perform
046562 MOVE ZEROES TO FLD-START
* count leading zeroes
046563 INSPECT IP-OCTET(IP-INDEX1) TALLYING FLD-
START
046564 FOR LEADING "0"
046576 IF FLD-START =
4
046577 THEN
* if the entire field are zeroes, then simply display "0:"
*at a later stage figure out the IP compaction convention
* of allowing one or more zero address fields to be compacted
*once* per
* address into a sequence of
"::"
046578 MOVE "0:" TO IP-PRINT-FIELD(IP-PRINT-POSITION:
2)
046579 ADD 2 TO IP-PRINT-
POSITION
046586 ELSE
* only suppress leading zeroes
* how many bytes to move?
046587 COMPUTE FLD-LENGTH = (4 - FLD-START)
* move them into the display field
046598 MOVE IP-OCTET(IP-INDEX1)(FLD-START + 1:FLD-
LENGTH)
046599 TO IP-PRINT-FIELD(IP-PRINT-POSITION:fld-
length)
* calculate next position in display field
046600 COMPUTE IP-PRINT-POSITION = (IP-PRINT-
POSITION + fld-length)
* add a colon (":")
046601 MOVE ":" TO IP-PRINT-FieLD(IP-PRINT-POSITION:
1)
* bump position in display field
046602 ADD 1 TO IP-PRINT-
POSITION
046613 END-
IF
046614 END-PERFORM
move 1 to fld-start
inspect IP-octet (IP-index1) tallying fld-start for leading zero
compute fld-length = length of IP-octet - fld-start + 1
string IP-octet(IP-index1) (fld-start: fld-length) ':'
delimited by size into IP-print-field(IP-print-position:fld-length+1)
add fld-length, 1 to IP-print-position
.
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