19 Jan
2008
19 Jan
'08
6:23 p.m.
Date: Fri, 18 Jan 2008 18:20:45 -0800
From: dwight elvey <dkelvey at hotmail.com>
For this, I need a little help. Since the 8 inch
drives were 32 sectored,
calculating tracks from a disk offset number was easy. 5.25 disk with 10
sectored will require something different. Is there an easy way to to
separate track from sector using Z80 code? Dwight
Do you mean "is there an easy way to divide by 10?". If so, yes:
0.100x = x/16+x/32+x/256+x/4096+x/8192
to about 0.04 percent (4 parts in 10,000). Truncate the series if
you need less accuracy. Ask if you need Z80 code.
Cheers,
Chuck
19 Jan
19 Jan
9:01 p.m.
New subject: div by 10 on Z80 was RE: Reading Polymorphic ---
From: cclist at sydex.com
Date: Fri, 18 Jan 2008 18:20:45 -0800
From: dwight elvey
Hi Chuck
I'm not sure how effective that would be in Z80 code. It looks
like I'd at least need to do 32 bit coding to keep track of things.
I'd still need to calculate the remainder when done( I need both ).
The maximum sector index would be 800 decimal. I came up
with the following code to do this all in Z80 code but I'm interested
both compact and fast, with more emphasis on compact.
Here is the code I've made so far:
; hl is value to be divided by 10
; max hl will be 800
; uses a, bc, de and hl
; returns a = quotient
; h = remainder
; uses 42 bytes
div10:
xor a
ld bc -640d
ld de 640d
call div10s
call div10s
call div10s
call div10s
call div10s
call div10s
call div10s
add hl,hl
ret
div10s:
add a,a
add hl,bc
jp c,div10s1
add hl,de
jp div10s2
div10s1:
inc a
div10s2:
add hl,hl
ret
After the first two calls, I could do the rest as byte operations
but I think the total byte cost would be greater.
I'm looking for other ideas on smaller code. It would be nice
to hace one more 8 bit register as a counter.
Dwight
_________________________________________________________________
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For this, I need a little help. Since the 8 inch
drives were 32 sectored,
calculating tracks from a disk offset number was easy. 5.25 disk with 10
sectored will require something different. Is there an easy way to to
separate track from sector using Z80 code? Dwight
Do you mean "is there an easy way to divide by 10?". If so, yes:
0.100x = x/16+x/32+x/256+x/4096+x/8192
to about 0.04 percent (4 parts in 10,000). Truncate the series if
you need less accuracy. Ask if you need Z80 code.
Cheers,
Chuck
20 Jan
20 Jan
5:02 p.m.
New subject: div by 10 on Z80 was RE: Reading Polymorphic ---
From: dkelvey at hotmail.com
Hi
Pete Turnbull sent some suggestions and here is what we have
now. It trades a little speed for size but the inner loop is faster
As I stated, faster is good but smaller is better. Any more help
would be great:
Next try at code:
div10:
xor a
ld de,#-640d ; largest power of 2 times 10 less then 800d
ld b,#7 ; only seven loops needed to finish divide 800/10
divloop:
call div10s ; divide steps
djnz divloop
add hl,hl ; push full remainder in HL
ret
div10s:
add a,a ; 2*a
add hl,de ; trial subtract
jr c,div10s1 ; carry means trial passed
sbc hl,de ; undo previous add, carry is clear
dec a ; to nullify the following inc
div10s1:
inc a ; add to quotient
add hl,hl ; shift number to reuse same constant, 640 decimal
ret
This is 23 bytes and looks good.
Dwight
_________________________________________________________________
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From: cclist at sydex.com
Date: Fri, 18 Jan 2008 18:20:45 -0800
From: dwight elvey
Hi Chuck
I'm not sure how effective that would be in Z80 code. It looks
like I'd at least need to do 32 bit coding to keep track of things.
I'd still need to calculate the remainder when done( I need both ).
The maximum sector index would be 800 decimal. I came up
with the following code to do this all in Z80 code but I'm interested
both compact and fast, with more emphasis on compact.
Here is the code I've made so far:
; hl is value to be divided by 10
; max hl will be 800
; uses a, bc, de and hl
; returns a = quotient
; h = remainder
; uses 42 bytes
div10:
xor a
ld bc -640d
ld de 640d
call div10s
call div10s
call div10s
call div10s
call div10s
call div10s
call div10s
add hl,hl
ret
div10s:
add a,a
add hl,bc
jp c,div10s1
add hl,de
jp div10s2
div10s1:
inc a
div10s2:
add hl,hl
ret
After the first two calls, I could do the rest as byte operations
but I think the total byte cost would be greater.
I'm looking for other ideas on smaller code. It would be nice
to hace one more 8 bit register as a counter.
Dwight
For this, I need a little help. Since the 8 inch
drives were 32 sectored,
calculating tracks from a disk offset number was easy. 5.25 disk with 10
sectored will require something different. Is there an easy way to to
separate track from sector using Z80 code? Dwight
Do you mean "is there an easy way to divide by 10?". If so, yes:
0.100x = x/16+x/32+x/256+x/4096+x/8192
to about 0.04 percent (4 parts in 10,000). Truncate the series if
you need less accuracy. Ask if you need Z80 code.
Cheers,
Chuck
21 Jan
21 Jan
4:57 a.m.
New subject: div by 10 on Z80 was RE: Reading Polymorphic ---
dwight elvey wrote:
Hi
Pete Turnbull sent some suggestions and here is what we have
now. It trades a little speed for size but the inner loop is faster
As I stated, faster is good but smaller is better. Any more help
would be great:
Next try at code:
div10:
xor a
ld de,#-640d ; largest power of 2 times 10 less then 800d
ld b,#7 ; only seven loops needed to finish divide 800/10
divloop:
call div10s ; divide steps
djnz divloop
add hl,hl ; push full remainder in HL
ret
div10s:
add a,a ; 2*a
add hl,de ; trial subtract
jr c,div10s1 ; carry means trial passed
sbc hl,de ; undo previous add, carry is clear
dec a ; to nullify the following inc
div10s1:
inc a ; add to quotient
add hl,hl ; shift number to reuse same constant, 640 decimal
ret
This is 23 bytes and looks good.
(I expect you may have noticed already..) the subroutine (div10s) is
only called once now, you could inline it to save another 4 bytes.
3:09 p.m.
New subject: div by 10 on Z80 was RE: Reading Polymorphic ---
Date: Sun, 20 Jan 2008 20:57:27 -0800
From: hilpert at cs.ubc.ca
To: General at priv-edmwaa04.telusplanet.net
CC:
Subject: Re: div by 10 on Z80 was RE: Reading Polymorphic ---
dwight elvey wrote:
Hi
Yes, I saw that after posting.
Thanks
Dwight
_________________________________________________________________
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Hi
Pete Turnbull sent some suggestions and here is what we have
now. It trades a little speed for size but the inner loop is faster
As I stated, faster is good but smaller is better. Any more help
would be great:
Next try at code:
div10:
xor a
ld de,#-640d ; largest power of 2 times 10 less then 800d
ld b,#7 ; only seven loops needed to finish divide 800/10
divloop:
call div10s ; divide steps
djnz divloop
add hl,hl ; push full remainder in HL
ret
div10s:
add a,a ; 2*a
add hl,de ; trial subtract
jr c,div10s1 ; carry means trial passed
sbc hl,de ; undo previous add, carry is clear
dec a ; to nullify the following inc
div10s1:
inc a ; add to quotient
add hl,hl ; shift number to reuse same constant, 640 decimal
ret
This is 23 bytes and looks good.
(I expect you may have noticed already..) the subroutine (div10s) is
only called once now, you could inline it to save another 4 bytes.
6187
days inactive
6189
days old
4 comments
3 participants
participants (3)
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cclist＠sydex.com -
dkelvey＠hotmail.com -
hilpert＠cs.ubc.ca