8051 code to find Permutation and Combination

8051 code to find permutation and combination

This program finds the value of permutation and combination for given two input numbers

 Algorithm

1) Store the value of n to R0,store the value of r to R1 and store the value (n-r) to R2.
2) Compare if n>r continue the process, if n<r then stop computation, if n=r then assign permutation as n! and combination as 1.
3) Calculate the n!,r!,(n-r)! and store in R3,R4,R5 respectively.
4) Calculate permutation by dividing n!/(n-r)!
5) Calculate combination by dividing n!/(n-r)!*r!

Code goes here:

org 0000h
ljmp main
org 40h
main:          MOV R0,#04 ; value of n
               MOV R1,#02 ; value of r
               MOV A,R0
               MOV B,R1
               CJNE A,B,CHECK ; to check whether n is greater than r
               LJMP COMPUTE
CHECK:         JC STOP         ; jump to stop if n<r
               SUBB A,R1
               MOV R2,A        ; the value of n-r
               MOV A,R0
LABEL1:        DEC R0
               MOV B,R0
               MUL AB
               CJNE R0,#01,LABEL1
               MOV R3,A        ; the value of n!
               MOV A,R1
LABEL2:        DEC R1
               MOV B,R1
               MUL AB
               CJNE R1,#01,LABEL2
               MOV R4,A        ; the value of r!
               MOV A,R2
LABEL3:        DEC R2
               MOV B,R2
               MUL AB
               CJNE R1,#01,LABEL3
               MOV R5,A        ; the value of n-r!
               MOV A,R3
               MOV B,R5
               DIV AB         ; dividing n!/(n-r)!
               MOV R6,A        ; storing the result of permutation
               MOV B,R4 
               DIV AB          ; dividing n!/(n-r)!*r!
               MOV R7,A        ; storing the result of combination
               LJMP STOP
COMPUTE:       DEC R0         ; it stores the value of permutation=n! if n=r
               MOV B,R0
               MUL AB
               CJNE R0,#01,LABEL1
               MOV R6,A        ; the result of permutation=n! if n=r
STOP:          MOV R7,#01      ; it stores the value of combination=1 if n=r
    END