nCr_HL_DE

;===============================================================
nCrHL_DE:
;===============================================================
;Inputs:
;     hl is "n"
;     de is "r"
;Outputs:
;     interrupts off
;     a is 0
;     bc is an intermediate result
;     de is "n"
;     hl is the result
;     a' is not changed
;     bc' is "r"+1
;     de' is the same as bc
;     hl' is "r" or the compliment, whichever is smaller
;===============================================================
     or a                     ;reset carry flag
     sbc hl,de
     ret c                    ;r should not be bigger than n
     sbc hl,de \ add hl,de
     jr nc,$+3
       ex de,hl
                             ;hl is R
     push de
     ld bc,1                 ;A
     exx
     pop de                  ;N
     ld bc,1                 ;C
     ld h,b \ ld l,c         ;D
nCrLoop:
     push de
     push hl
     call DE_Times_BC
     push hl \ exx \ pop de
     push hl
     call DE_Div_BC
     pop de
     push hl \ ex de,hl \ exx \ pop hl
     ld b,h \ ld c,l
     pop de \ add hl,de
     pop de \ inc de
     exx
     inc bc
     or a \ sbc hl,bc \ add hl,bc
     exx
     jr nc,nCrLoop
     ret