Bill Cornutt wrote:

> And a right shift of the 200 value gives a 100 value.   The same
> shifting 80 to get the next compare/subtraction value...
> Is a shift quicker than a load?

  If the value is in a file register and the carry is already clear,
yes.  This is particularly useful if you extend this procedure to multi-
byte values.

> Also if the 'test for 80' is true, then no need to 'test for 40'

  Well, Osama ALASSIRY <osama@ALASSIRY.COM> suggested code:

> Improving the method discussed earlier:
> taking X=byte and converting to BCD digits H,T,U
>
>  H=0
>  T=0
>  U=X
>  if U>=200 then H=H+2: U=U-200: Goto Check40 'NUMBER WILL BE <=55
>  if U>=100 then H=H+1: U=U-100
>  if U>=80 then T=T+8: U=U-80: Goto Check10 'NUMBER WILL BE <=19
> Check40:
>  if U>=40 then T=T+4: U=U-40
>  if U>=20 then T=T+2: U=U-20
> Check10:
>  if U>=10 then T=T+1: U=U-10

  If you are using fixed subtractions rather than shifts, and since each
"IF" is coded <skip conditional> <GOTO else code> <IF code> (<GOTO ...>)
<else code> then the one-instruction-less optimisation of the above is:

H=0: T=0: U=X

C200:
 if U=>200 goto CG200
C100:
 if U<100 goto C80
 H=H+1: U=U-100
C80:
 if U<80 goto C40
 T=T+8: U=U-80
 goto C10

CG200:
 H=H+2: U=U-200
C40:
 if U<40 goto C20
 T=T+4: U=U-40
C20:
 if U<20 goto C10
 T=T+2: U=U-20
C10:
 if U<10 goto C00
 T=T+1: U=U-10
C00:

  FWIW!

  Cheers,
        Paul B.