****************************************
* 16 x 8 bit integer divide

* Result must be an 8 bit value

* ENTRY: A = divisor
*        X = dividend

* EXIT:  A = remainder
*        B = quotient
*        all other registers (except CC) preserved

 nam 16x8 bit Divide
 ttl Assembler Library Module


 section .bss
negcount rmb 1
 endsect

 section .text

* Signed Divide
SDIV168:
 clr negcount,u
 PSHS A,X
 tst ,s
 bpl testquo
 lda ,s
 coma
 inca
 sta ,s
 inc negcount,u
testquo
 tst 1,s
 bpl ok
 ldd 1,s
 comb
 coma
 addd #$0001
 std 1,s
 inc negcount,u
ok
 puls a,x
 bsr DIV168
 dec negcount,u
 bne goforit
 pshs a,x
 lda ,s
 coma
 inca
 sta ,s
 ldd 1,s
 coma
 comb 
 addd #$0001
 std 1,s 
 puls a,x
goforit
 rts


DIV168:
 LDB #8 bit counter
 PSHS A,B,X save count and divisor and value
 TFR X,D put dividend in D

div1
 ASLB shift dividend and quotient
 ROLA
 CMPA 0,S is trial subtraction successful?
 BCS div2
 SUBA 0,S yes, subtract and set bit
 INCB in quotient

div2
 DEC 1,S count down bits
 BNE div1 loop till done
 LEAS 2,S clean stack
 PULS X,PC return

 endsect