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Special cased the division 16 by 8.

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git-svn-id: svn://svn.cc65.org/cc65/trunk@4043 b7a2c559-68d2-44c3-8de9-860c34a00d81
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uz 2009-08-19 14:51:16 +00:00
parent b9c0d6ac85
commit c4763e9007
1 changed files with 46 additions and 14 deletions
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60
libsrc/runtime/udiv.s
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@ -5,11 +5,12 @@
;
.export tosudiva0, tosudivax, udiv16
.import popsreg
.importzp sreg, ptr1, ptr4
.import popsreg
.importzp sreg, ptr1, ptr4
tosudiva0:
ldx #0
ldx #$00 ; Clear high byte
tosudivax:
sta ptr4
stx ptr4+1 ; Save right operand
@ -25,30 +26,61 @@ tosudivax:
ldx sreg+1
rts
; Do (sreg/ptr4) -> sreg (see mult-div.s from "The Fridge").
;---------------------------------------------------------------------------
; 16by16 division. Divide sreg by ptr4. Result is in sreg, remainder in ptr1
; (see mult-div.s from "The Fridge").
; This is also the entry point for the signed division
udiv16: lda #0
sta ptr1+1
ldy #16
ldx sreg+1
beq udiv16by8a
L0: asl sreg
rol sreg+1
rol a
rol ptr1+1
pha
cmp ptr4
lda ptr1+1
sbc ptr4+1
bcc L1
sta ptr1+1
pla
sbc ptr4
pha
inc sreg
bcc L1
sta ptr1+1
pla
sbc ptr4
pha
inc sreg
L1: pla
dey
bne L0
sta ptr1
rts
dey
bne L0
sta ptr1
rts
;---------------------------------------------------------------------------
; 16by8 division
udiv16by8:
lda #0
sta ptr1+1
ldy #16
udiv16by8a:
@L0: asl sreg
rol sreg+1
rol a
bcs @L1
cmp ptr4
bcc @L2
@L1: sbc ptr4
inc sreg
@L2: dey
bne @L0
sta ptr1
rts