Divide by 10

GAF

In the September issue if Nuts & Volts there was an article on floating point math on a 8-bit·chip.· Using what the author outlined I came up with a simple routine to divide a byte by 10 and determine the remainder.· This routine only involves simple shift and add instructions. In the following code X is the byte that will be divided by 10, tmp1 and tmp2 are just temporary variables. The "Result" contains the answer to the division.

tmp1 = X>>2
tmp1 = tmp1 + X
tmp2 = tmp1>>1
tmp2 = tmp2 + X
Result= tmp2>>4

tmp1 = Result<<2
tmp1 = tmp1 + Result
tmp2 = tmp1 << 1
Remainder = X - tmp2

I have used this routine in a couple of my SX programs and it seems to work fine.

Bean

Unless tmp1 and tmp2 are WORD variables, they will overflow.

Here is what I suggest for a fast divide by 10 with remainder:

' Byte divide by 10 with remainder DEVICE SX28, OSC4MHZ, TURBO, STACKX, OPTIONX
FREQ 4_000_000
 
x         VAR BYTE
result    VAR BYTE
remainder VAR BYTE
 
PROGRAM Start NOSTARTUP

 
Start:
  x = 0
 
  ASM 'Divide by 10
    MOV remainder,x
    CLR result
    MOV W,#160
    SUB remainder,W
    RL result
    SB result.0
    ADD remainder,W
    MOV W,#80
    SUB remainder,W
    RL result
    SB result.0
    ADD remainder,W
    MOV W,#40
    SUB remainder,W
    RL result
    SB result.0
    ADD remainder,W
    MOV W,#20
    SUB remainder,W
    RL result
    SB result.0
    ADD remainder,W
    MOV W,#10
    SUB remainder,W
    RL result
    SB result.0
    ADD remainder,W
 ENDASM
 'result = x / 10
 'remainder = x // 10
END

This is basicly and "unrolled" version of the normal division code.

Bean

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Post Edited (Bean (Hitt Consulting)) : 9/9/2007 1:05:31 PM GMT

GAF

Thanks Bean, I will give it a try. I see your point on my routine.