Factorial: Difference between revisions
Added solution for EDSAC
(→{{header|PL/0}}: Added a solution.) |
(Added solution for EDSAC) |
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at run() (test.x:19)
at ^ShowFactorials (CallLaterRequest: native)
</pre>
=={{header|EDSAC order code}}==
<syntaxhighlight lang="edsac">
[Demo of subroutine to calculate factorial.
EDSAC program, Initial Orders 2.]
[Arrange the storage]
T45K P56F [H parameter: subroutine for factorial]
T46K P80F [N parameter: library subroutine P7 to print integer]
T47K P128F [M parameter: main routine]
[================================ H parameter ================================]
E25K TH
[Subroutine for N factorial. Works for 0 <= N <= 13 (no checking done).
Input: 17-bit integer N in 6F (preserved).
Output: 35-bit N factorial is returned in 0D.
Workspace: 7F]
GK
A3F T19@ [plant return link as usual]
TD [clear the whole of 0D, including the sandwich bit]
A20@ TF [0D := 35-bit 1]
A6F T7F [7F = current factor, initialize to N]
E15@ [jump into middle of loop]
[Head of loop: here with 7F = factor, acc = factor - 2]
[8] H7F [mult reg := factor]
A20@ [acc := factor - 1]
T7F [update factor, clear acc]
VD [acc := 0D times factor]
L64F L64F [shift 16 left (as 8 + 8) for integer scaling]
TD [update product, clear acc]
[15] A7F S2F [is factor >= 2 ? (2F permanently holds P1F)]
E8@ [if so, loop back]
T7F [clear acc on exit]
[19] ZF [(planted) return to caller]
[20] PD [constant: 17-bit 1]
[================================ M parameter ================================]
E25K TM GK
[Main routine]
[Teleprinter characters]
[0] K2048F [1] #F [letters mode, figures mode]
[2] FF [3] AF [4] CF [5] VF [F, A, C, equals]
[6] !F [7] @F [8] &F [space, carriage return, line feed]
[Enter here with acc = 0]
[9] TD [clear the whole of 0D, including the sandwich bit]
A33@ [load 17-bit number N whose factorial is required]
UF [store N in 0D, extended to 35 bits for printing]
T6F [also store N in 6F, for factorial subroutine]
O1@ [set teleprinter to figures]
[14] A14@ GN [print N (print subroutine preserves 6F)]
[Print " FAC = " (EDSAC teleprinter had no exclamation mark)]
O@ O6@ O2@ O3@ O4@ O1@ O6@ O5@ O6@
[25] A25@ GH [call the above subroutine, 0D := N factorial]
[27] A27@ GN [call subroutine to print 0D]
O7@ O8@ [print CR, LF]
O1@ [print dummy character to flush teleprinter buffer]
ZF [stop]
[33] P6D [constant: 17-bit 13]
[================================ N parameter ================================]
E25K TN
[Library subroutine P7, prints long strictly positive integer in 0D.
10 characters, right justified, padded left with spaces.
Even address; 35 storage locations; working position 4D.]
GKA3FT26@H28#@NDYFLDT4DS27@TFH8@S8@T1FV4DAFG31@SFLDUFOFFFSFL4F
T4DA1FA27@G11@XFT28#ZPFT27ZP1024FP610D@524D!FO30@SFL8FE22@
[============================= M parameter again =============================]
E25K TM GK
E9Z [define entry point]
PF [acc = 0 on entry]
[end]
</syntaxhighlight>
{{out}}
<pre>
13 FAC = 6227020800
</pre>
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