[Farey sequence for Rosetta Code website.
  EDSAC program, Initial Orders 2.
  Prints Farey sequences up to order 11
  (or other limit determined by a simple edit).]

 [Modification of library subroutine P6.
  Prints number (absolute value <= 65535)
  passed in 0F, without leading spaces.
  41 locations.]
          T 56 K
  GKA3FT35@SFG11@UFS40@E10@O40@T4FE35@O@T4F
  H38@VFT4DA13@TFH39@S16@T1FV4DU4DAFG36@TFTF
  O5FA4DF4FS4FL4FT4DA1FS13@G19@EFSFE30@J995FJFPD

          T 100 K
          G     K
  [Maximum order to be printed. For convenience, entered as
  an address, not an integer, e.g. 'P 11 F' not 'P 5 D'.]
    [0]   P  11 F [<--- edit here]
  [Other constants]
    [1]   P     D [1]
    [2]   #     F [figure shift]
    [3]   X     F [slash]
    [4]   !     F [space]
    [5]   @     F [carriage return]
    [6]   &     F [line feed]
    [7]   K4096 F [teleprinter null]
  [Variables]
    [8]   P     F [n, order of current Farey sequence]
    [9]   P     F [maximum n + 1, as integer]
          [a/b and c/d are consecutive terms of the Farey sequence]
   [10]   P     F [a]
   [11]   P     F [b]
   [12]   P     F [c]
   [13]   P     F [d]
   [14]   P     F [t, temporary store]

          [Subroutine to print c/d]
   [15]   A   3 F [plant link for return]
          T  26 @
          A  12 @ [load c]
          T     F [to 0F for printing]
   [19]   A  19 @ [for subroutine return]
          G  56 F [print c]
          O   3 @ [print '/']
          A  13 @ [load d]
          T     F [to 0F for printing]
   [24]   A  24 @ [for subroutine return]
          G  56 F [print d]
   [26]   E     F [return]

           [Main routine.
           Enter with accumulator = 0.]
   [27]   O   2 @ [set teleprinter to figures]
          A     @ [max order as address]
          R     D [shift 1 right to make integer]
          A   1 @ [add 1]
          T   9 @ [save for comparison]
          A   1 @ [start with order 1]
          [Here with next order (n) in the accumulator]
   [33]   S   9 @ [subtract (max order) + 1]
          E  84 @ [exit if over maximum]
          A   9 @ [restore after test]
          T   8 @ [store]
          [Prefix the Farey sequence with a formal term -1/0.
           The second term is calculated from this and the first term.]
          S   1 @ [acc := -1]
          T  10 @ [a := -1]
          T  11 @ [b := 0]
          T  12 @ [c := 0]
          A   1 @ [d := 1]
          T  13 @
          A  43 @ [for subroutine return]
          G  15 @ [call subroutine to print c/d]

          [Calculate next term; basically same as Wikipedia method]
   [45]   T     F [clear acc]
          A  10 @ [t := a]
          T  14 @
          A  12 @ [a := c;]
          T  10 @
          S  14 @ [c := -t]
          T  12 @
          A  11 @ [t := b]
          T  14 @
          A  13 @ [b := d]
          T  11 @
          S  14 @ [d := -t]
          T  13 @
          A   8 @ [t := n + t]
          A  14 @
          T  14 @
          [Inner loop, get t div b by repeated subtraction]
   [61]   A  14 @ [t := t - b]
          S  11 @
          G  72 @ [jump out when t < 0]
          T  14 @
          A  12 @ [c := c + a]
          A  10 @
          T  12 @
          A  13 @ [d := d + b]
          A  11 @
          T  13 @
          E  61 @ [loop back (always, since acc = 0)]
          [End of inner loop, print c/d preceded by space]
   [72]   O   4 @
          T     F
   [74]   A  74 @ [for subroutine return]
          G  15 @ [call subroutine to print c/d]
          A   1 @ [form 1 - d, to test for d = 1]
          S  13 @
          G  45 @ [if d > 1, loop for next term]
          O   5 @ [else print end of line (CR LF)]
          O   6 @

          [Next Farey series.]
          A   8 @ [load order]
          A   1 @ [add 1]
          E  33 @ [loop back]

          [Here when finished]
   [84]   O   7 @ [output null to flush teleprinter buffer]
          Z     F [stop]
          E  27 Z [define start of execution]
          P     F [start with accumulator = 0]