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Fix the move D, command.

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Alexander Noack
2026-04-19 23:10:29 +02:00
parent 7439e26a69
commit 8a27297c16
1 changed files with 21 additions and 7 deletions
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28
src/chkmat.s
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@@ -18,26 +18,40 @@ DONE: .LOGOUT 2, ;Exit from the program
;Subroutine that checks a byte array, where one byte is a 4-bit value,
;for duplicate values.
;The algorithm works as follows:
;The original word is walked through in for bit steps. Each 4-bit value
;The original word is walked through in 4-bit steps. Each 4-bit value
;is read, and its value is used as a bit pointer to the 'hashing'-register.
;If a number is found, the bit in the hashing register is set. If the bit
;is already set, the number has already been found the in original set.
;is already set, the number has already been found the in original data.
;To make the walk through easy, we use a special feature of the PDP-10:
;We access the data register, as if it was a memory address.
;The following registers are used:
;A: Accumulator used to store the values that are read from the data field.
;B: Used to check if a bit is set, without destroying the contents of I.
;C: Contains the data field itself: 36 bits, in 4-bit segments.
;D: Contains the result, 0 if successfull, else >0.
;E: Used as a table to store if a number was found in the field.
;X: The byte pointer to the data field.
CHKMAT: PUSH P,A ;Save the register A
PUSH P,B ;Save the B-register
PUSH P,C ;Save the data register
PUSH P,E ;Save the E register
PUSH P,X ;Save the index register
SET E ;Set the hash register to 0.
MOVEI D,11 ;Load D with 16.
SETZ E ;Set the hash register to 0.
MOVE X,[440400,,C] ;Store a byte pointer to C
LOOP: ILDB A,X ;Store a byte in A
MOVEI B,E ;Copy the table.
LSH B,A ;Shift out the bit to check.
ANDI B,1 ;Check if the first bit is set.
CKLOOP: SOJE D,CHKEXT ;All bits set?
ILDB A,X ;Store a byte in A
MOVEI B,1 ;Set B to 1
LSH B,A ;Set the Ath bit in the mask
TRNE E,B ;Test, if a bit is already set
JRST CHKEXT ;Double value found, exit.
IORI E,B ;Set the Ath bit in the code
JRST LOOP ;Back to the loop
CHKEXT: POP P,X ;Restore X
POP P,E ;Restore E
POP P,C ;Restore C
POP P,B ;Restore B
POP P,A ;Restore A
POPJ P, ;Return from function