I decided to learn COBOL because… well…
Since I learn best by doing, I wanted a small project to get my hands dirty. Most COBOL samples I found were simple “Hello, world!” type projects or domain-specific finance stuff. I went for something different and implemented the MT19937 PRNG. Anyway, here’s the rest of the fucking owl.
>>DEFINE CONSTANT N 624
>>DEFINE CONSTANT M 397
>>DEFINE CONSTANT W 32
>>DEFINE CONSTANT R 31
>>DEFINE CONSTANT A 2567483615 *> 0x9908b0dfUL
>>DEFINE CONSTANT U 11
>>DEFINE CONSTANT S 7
>>DEFINE CONSTANT T 15
>>DEFINE CONSTANT L 18
>>DEFINE CONSTANT B 2636928640 *> 0x9d2c5680UL
>>DEFINE CONSTANT C 4022730752 *> 0xefc60000UL
>>DEFINE CONSTANT D 4294967295 *> 0xffffffffUL
>>DEFINE CONSTANT F 1812433253
IDENTIFICATION DIVISION.
PROGRAM-ID. mt19937.
AUTHOR. dodslaser.
ENVIRONMENT DIVISION.
CONFIGURATION SECTION.
REPOSITORY.
FUNCTION ALL INTRINSIC.
DATA DIVISION.
WORKING-STORAGE SECTION.
01 STATE-TABLE.
05 STATE OCCURS N TIMES BINARY-LONG UNSIGNED.
77 UMASK BINARY-LONG UNSIGNED.
77 LMASK BINARY-LONG UNSIGNED.
77 IDX BINARY-SHORT UNSIGNED.
77 N-VALUES BINARY-SHORT UNSIGNED.
77 CHR-N-VALUES PIC Z(5).
77 SEED BINARY-LONG UNSIGNED.
77 CHR-SEED PIC Z(10).
77 X BINARY-LONG UNSIGNED.
77 Y BINARY-LONG UNSIGNED.
77 CHR-Y PIC Z(10).
PROCEDURE DIVISION.
ACCEPT SEED FROM ENVIRONMENT "SEED"
ON EXCEPTION MOVE 5489 TO SEED.
MOVE SEED TO CHR-SEED.
DISPLAY "MT19937 (Seed: " TRIM(CHR-SEED) ")".
ACCEPT N-VALUES FROM ENVIRONMENT "N"
ON EXCEPTION MOVE 10 TO N-VALUES.
MOVE N-VALUES TO CHR-N-VALUES.
DISPLAY "Generating " TRIM(CHR-N-VALUES) " values".
COMPUTE UMASK = 4294967295 B-SHIFT-L R.
COMPUTE LMASK = 4294967295 B-SHIFT-R (W - R).
MOVE SEED TO STATE(1).
PERFORM VARYING IDX FROM 2 BY 1
UNTIL IDX = N
COMPUTE STATE(IDX) =
STATE(IDX - 1)
B-SHIFT-R (W - 2)
B-XOR STATE(IDX - 1) * F + IDX - 1
B-AND ((1 B-SHIFT-L W) - 1)
END-PERFORM.
DISPLAY SPACE.
PERFORM N-VALUES TIMES
PERFORM TEMPER
MOVE Y TO CHR-Y
DISPLAY HEX-OF(Y) " : " TRIM(CHR-Y)
END-PERFORM.
TWIST.
PERFORM VARYING IDX FROM 1 BY 1
UNTIL IDX = N
COMPUTE X =
STATE(IDX)
B-AND UMASK
+ STATE(MOD(IDX, N) + 1)
COMPUTE STATE(IDX) =
X
B-AND LMASK
B-SHIFT-R 1
B-XOR (A * MOD(X, 2))
B-XOR STATE(MOD(IDX + M, N))
END-PERFORM.
MOVE 1 TO IDX.
TEMPER.
IF IDX = N THEN PERFORM TWIST END-IF.
MOVE STATE(IDX) TO Y.
COMPUTE Y = Y B-XOR ((Y B-SHIFT-R U) B-AND D).
COMPUTE Y = Y B-XOR ((Y B-SHIFT-L S) B-AND B).
COMPUTE Y = Y B-XOR ((Y B-SHIFT-L T) B-AND C).
COMPUTE Y = Y B-XOR (Y B-SHIFT-R L).
COMPUTE Y = Y B-AND ((1 B-SHIFT-L W) - 1).
COMPUTE IDX = IDX + 1.
The above code compiles with cobc (GnuCOBOL) 3.2.0. You can control the seed with the SEED and the number of values to generate with the N environment variables.
I imagine any elder COBOL wizard reading this is probably angrily shaking their wrinkly old fist at the screen, cursing me for wasting precious punch-card space, or not sacrificing the correct number of goats to the right deities in the RITUAL SACRIFICE DIVISION.. If this is you, feel free to open an issue, and I will try to atone for my sins. On a semi-related note, I strongly suspect this would not run on an actual mainframe. Again, feel free to prove me wrong.
Now, if you’ll excuse me, I must go scream into PILLOW DIVISION..