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Hackers’ Corner: Unlocking Functions in Dyalog APL for MS DOS

by Ray Cannon

Vector 7:2, page 132

implementations system interfaces

Transcribed from the printed issue; not yet reviewed. Read it in the PDF of the issue, page 132

By comparing DYALOG APL workspaces as DOS files, it is easy to discover that locked functions differ from unlocked functions by a single byte. Unlocked functions have a marker of hex 23, but in locked functions, this marker is hex 33.

So here is how to unlock a locked function. (To simplify the explanation, I will use a function called FOO and a temporary workspace named LOCK.)

First copy the function FOO into a clear ws. Save this workspace as LOCK. (Don't name the ws the same as the locked function as this might cause difficulties later.) Exit back to DOS.

Change directory to the one holding your newly saved ws. Now using DEBUG modify the HEX 33 to HEX 23 viz:- Enter DEBUG thus: DEBUG LOCK.DWS<enter> Then after DEBUG's prompt (a minus sign) type: L 0<enter> This will load the file starting at offset 0. Then locate the locked function by searching for it thus:- S 0,700 46 4F 4F<enter> Where 46 4F 4F is FOO (the function name) in hex. Debug will respond with its location thus:- 27F4:05C8 or some such numbers. Ask DEBUG to display its contents round there by typing: D 05C8<enter> DEBUG will respond with 8 lines of hex with text on the right. At the position 5C8 in the text will be the function name (FOO). In the HEX the function name will be followed by 00. This will be follow about 8 HEX numbers and then the all-important HEX 33. (In the text, this will display as the number 3.) If the HEX 33 is at location 5D4 you change it to HEX 23 by typing:- E 5D4 23<enter> You the write the change back to disk by typing:- W 0<enter> Debug will say "Writing 062c bytes" or some such. Then exit from DEBUG by typing:- Q<enter>

Now reload DYALOG APL, )COPY LOCK FOO and check FOO is unlocked. Simple!

Alternatively, you could write a function in APL to read LOCK as a DOS file into APL, modify the HEX 33 to 23, and write the data back out to the same DOS file. But I'll leave that up to you.