Changes
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...
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.
<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.
