.data
;----------------------------------
;
;----------------------------------
eight   db  8         ; mothafuckin 8
;----------------------------------
; GETBIT
;
; Input:
; - ax contains  the bit number requested ( 0 to 1783 are valid)
; - si points to the input compressed data string 1 to 223 bytes
;
; Output
; - if the requested bit number is valid (0 to 1783) then
;   ax contains the bit value 0 - 1
; - if the requested bit number is invalid  (greater than 1783)  then
;   ax is unchanged
; - the subroutine must save and restore any other used register
; - the input compressed data may not be changed
;----------------------------------
         .code                    ;
getbit:                           ;
     cmp    ax,1783       ; compare ax to 1783
     jg return        ; if ax > 1783, return
     cmp    ax,0          ; compare ax to 0
     jl return        ; if ax < 0, return
     push   bx        ; store bx
     push   cx        ; store cx
     div    [eight]       ; ah = remainder, al = quotient
     mov    bl,al         ; bx is byte offset
     mov    bh,0          ; convert bl to word
     mov    al,[bx+si]    ; looking at correct byte
         mov    cl,ah         ; cx is bit offset to CF
         mov    ch,0          ; convert ch to
     inc    cx        ; always loop once more
shift:                ;
     shl    al,1          ; shift left once
     loop   shift         ; loop cx times
restore:              ;
     pop    cx        ; restore cx
     pop    bx        ; restore bx
getflag:              ;
     jnc    zero          ; check the carry flag
     mov    ax,1          ; bit is a 1
     ret              ; return to main
zero:                 ;
     mov    ax,0          ; bit is a 0
return:               ;
         ret                      ; return bit
;----------------------------------
         end