Talk:Programming:Integer Multiplication - Revision history

Executioner at 01:41, 8 May 2007

2007-05-08T01:41:19Z

Prodatron at 09:51, 7 May 2007

2007-05-07T09:51:20Z

Executioner at 23:57, 6 May 2007

2007-05-06T23:57:48Z

Executioner: New page: The FastMult routine using logs can be optimised somewhat from it's original by removing the slow SET instructions and extra direct addressing operation:

 FastMult:   ld      l,c   l...

2007-05-06T23:42:55Z

New page: The FastMult routine using logs can be optimised somewhat from it's original by removing the slow SET instructions and extra direct addressing operation: <pre> FastMult: ld l,c l...

New page

The FastMult routine using logs can be optimised somewhat from it's original by removing the slow SET instructions and extra direct addressing operation:

<pre>
FastMult:
ld l,c
ld h,&82
ld d,(hl) ; d = 32 * log_2(c)

ld l,b
ld a,(hl) ; a = 32 * log_2(b)

add a,d
ld l,a
ld a,0
adc a,0
ld h,a ; hl = d + a

add hl,hl
set 2,h ; hl = hl + $0400
set 7,h ; hl = hl + &8000

ld e,(hl)
inc hl
ld d,(hl) ; de = 2^((hl)/32)

ret
</pre>

to

<pre>
FastMult:
ld l,c
ld h,&82
ld d,(hl) ; d = 32 * log_2(c)

ld l,b
ld a,(hl) ; a = 32 * log_2(b)

add a,d
ld l,a
adc &42
sub l
ld h,a ; hl = d + a

add hl,hl

ld e,(hl)
inc l
ld d,(hl) ; de = 2^((hl)/32)

ret
</pre>

The add hl,hl can also be removed if the tables are split with low-byte in one page and high-byte in the other.

← Older revision		Revision as of 01:41, 8 May 2007
Line 76:		Line 76:

	The two low and highbyte antilogtabs have to follow directly after the logtab. -- [[User:Prodatron\|Prodatron]] 11:51, 7 May 2007 (CEST)		The two low and highbyte antilogtabs have to follow directly after the logtab. -- [[User:Prodatron\|Prodatron]] 11:51, 7 May 2007 (CEST)
		+
		+	This is all well and good, but the routine is actually quite innacurate. [[User:Executioner\|Executioner]] 03:41, 8 May 2007 (CEST)

← Older revision		Revision as of 09:51, 7 May 2007
Line 54:		Line 54:

	The add hl,hl can also be removed if the tables are split with low-byte in one page and high-byte in the other and changing the &42 to &84. Since there are 512 entries in the anti-log table, you'd need two INC L's.		The add hl,hl can also be removed if the tables are split with low-byte in one page and high-byte in the other and changing the &42 to &84. Since there are 512 entries in the anti-log table, you'd need two INC L's.
		+
		+	:So the more optimal way would look like this:
		+
		+	<pre>
		+	FastMult:
		+	ld l,c
		+	ld h,logtab/256
		+	ld a,(hl) ; a = 32 * log_2(c)
		+	ld l,b
		+	add (hl) ; cf,a = 32 * log_2(c) + 32 * log_2(b)
		+	ld l,a
		+	ld a,h
		+	adc 1
		+	ld h,a
		+	ld e,(hl)
		+	inc h
		+	inc h
		+	ld d,(hl) ; de = 2^((hl)/32)
		+	ret
		+	</pre>
		+
		+	The two low and highbyte antilogtabs have to follow directly after the logtab. -- [[User:Prodatron\|Prodatron]] 11:51, 7 May 2007 (CEST)

← Older revision		Revision as of 23:57, 6 May 2007
Line 53:		Line 53:
	</pre>		</pre>

−	The add hl,hl can also be removed if the tables are split with low-byte in one page and high-byte in the other.	+	The add hl,hl can also be removed if the tables are split with low-byte in one page and high-byte in the other and changing the &42 to &84. Since there are 512 entries in the anti-log table, you'd need two INC L's.