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cc65/libsrc/runtime/udiv.s
uz 4a32e84639 Fixed an error in the division routine: The high byte of the wrong 16 bit
value was checked before entering the faster 16b8 division routine.


git-svn-id: svn://svn.cc65.org/cc65/trunk@4904 b7a2c559-68d2-44c3-8de9-860c34a00d81
2011-01-11 17:08:29 +00:00

83 lines
1.2 KiB
ArmAsm

;
; Ullrich von Bassewitz, 07.08.1998
;
; CC65 runtime: division for unsigned ints
;
.export tosudiva0, tosudivax, udiv16
.import popsreg
.importzp sreg, ptr1, ptr4
tosudiva0:
ldx #$00 ; Clear high byte
tosudivax:
sta ptr4
stx ptr4+1 ; Save right operand
jsr popsreg ; Get left operand
; Do the division
jsr udiv16
; Result is in sreg, remainder in ptr1
lda sreg
ldx sreg+1
rts
;---------------------------------------------------------------------------
; 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 ptr4+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
L1: pla
dey
bne L0
sta ptr1
rts
;---------------------------------------------------------------------------
; 16by8 division
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