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sqrt10.a
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sqrt10.a
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; https://github.com/TobyLobster/sqrt_test/blob/main/sqrt/sqrt10.a
; My tweaking of sqrt1.a, which was based on https://codebase64.org/doku.php?id=base:fast_sqrt
MLO = $02
MHI = $03
THI = $04
* = $0200
start
ldy #0 ; R = 0
; iteration one
lda MHI ;
cmp #$40 ;
bcc ++ ;
sbc #$40 ;
ldy #$80 ; R = R OR D
++
asl MLO ;
rol ; M = M ASL 1
sta MHI ; M = M - T
; iteration two
tya ;
ora #$20 ;
sta THI ; (R ASL 8) | (D ASL 7)
lda MHI ;
bcs + ; M >= 65536? then T <= M is always true
cmp THI ;
bcc ++ ; T <= M
+
sbc THI ;
sta MHI ; M = M - T
tya ;
ora #$40 ; set bit
tay ; R = R OR D
++
asl MLO
rol MHI ; M = M ASL 1
; iteration three
tya ;
ora #$10 ;
sta THI ; (R ASL 8) | (D ASL 7)
lda MHI ;
bcs + ; M >= 65536? then T <= M is always true
cmp THI ;
bcc ++ ; T <= M
+
sbc THI ;
sta MHI ; M = M - T
tya ;
ora #$20 ; set bit
tay ; R = R OR D
++
asl MLO ;
rol MHI ; M = M ASL 1
; iteration four
tya ;
ora #$08 ;
sta THI ; (R ASL 8) | (D ASL 7)
lda MHI ;
bcs + ; M >= 65536? then T <= M is always true
cmp THI ;
bcc ++ ; T <= M
+
sbc THI ;
sta MHI ; M = M - T
tya ;
ora #$10 ; set bit
tay ; R = R OR D
++
asl MLO ;
rol MHI ; M = M ASL 1
; iteration five
tya ;
ora #$04 ;
sta THI ; (R ASL 8) | (D ASL 7)
lda MHI ;
bcs + ; M >= 65536? then T <= M is always true
cmp THI ;
bcc ++ ; T <= M
+
sbc THI ;
sta MHI ; M = M - T
tya ;
ora #$08 ; set bit
tay ; R = R OR D
++
asl MLO ;
rol MHI ; M = M ASL 1
; iteration six
tya ;
ora #$02 ;
sta THI ; (R ASL 8) | (D ASL 7)
lda MHI ;
bcs + ; M >= 65536? then T <= M is always true
cmp THI ;
bcc ++ ; T <= M
+
sbc THI ;
; from this point on, A holds MHI, so no need to store it
; sta MHI ; M = M - T
; instead of this...
;tya ;
;ora #$04 ; set bit
;tay ; R = R OR D
; ...do this (it takes 2 cycles longer, but preserves A to avoid more expensive instructions)
iny ;
iny ;
iny ;
iny ;
++
asl MLO ;
rol ; M = M ASL 1
; iteration seven
; instead of this...
;tya ;
;ora #$01 ;
;sta THI ; (R ASL 8) | (D ASL 7)
; ... do this (same timing, but one byte shorter, and doesn't use A):
iny ;
sty THI ;
dey ;
; lda MHI ;
bcs + ; M >= 65536? then T <= M is always true
cmp THI
bcc ++ ; T <= M
+
sbc THI ; M = M - T
; instead of this...
;tya ;
;ora #$02 ; set bit
;tay ; R = R OR D
; ...do this (quicker, shorter, and preserves A)
iny ;
iny ;
++
asl MLO ;
rol ; M = M ASL 1
; last iteration (iteration eight)
bcs + ;
sty THI ;
asl MLO ;
sbc THI ; M = M - T
bcc ++ ;
+
iny ; R = R OR D (D is 1 here)
++
rts ;