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This is a program written in Sinclair BASIC (48 BASIC) for the Sinclair ZX Spectrum. It uses a hardcoded key (null right now) as seen in the bottom and outputs a stream of integers generated with RC4. Is there any way I can improve this particularly to get around 48 BASIC using one-indexed arrays (which makes RC4 hard to do without a lot of integer additions)?

  10 READ L
  20 DIM K(L)
  30 FOR I=1 TO L
  40 READ K(I)
  50 NEXT I
  60 DEF FN M(A,B)=A-INT (A/B)*B
  65 REM KSA
  70 DIM S(256)
  80 FOR I=0 TO 255
  90 LET S(I+1)=I
 100 NEXT I
 110 LET J=0
 120 FOR I=0 TO 255
 130 LET T=S(I+1)+K(FN M(I,L)+1)
 140 LET J=FN M(J+T,256)
 150 GO SUB 250
 160 NEXT I
 165 REM PRGA
 170 LET I=0
 180 LET J=0
 190 LET I=FN M(I+1, 256)
 200 LET J=FN M(J+S(I+1),256)
 210 GO SUB 250
 220 LET T=S(I+1)+S(J+1)
 230 PRINT S(FN M(T,256)+1)
 240 GO TO 190
 245 REM SWAP
 250 LET T=S(I+1)
 260 LET S(I+1)=S(J+1)
 270 LET S(J+1)=T
 280 RETURN
 285 REM KEY
 290 DATA 5
 300 DATA 0,0,0,0,0

KSA is the Key Scheduling Algorithm which initializes a 256-element array S with a permutation based on the key K (an array of size L). PRGA is the Pseudo-Random Generator Algorithm which prints a single integer to the screen at a time based on the contents of S.

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