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cc65/libsrc/runtime/mul8.s
uz acd1233bf2 Greatly improved multiplication routine. Optimized the generic 16x16 one and
added special cases for 8x16 and 8x8. The former is directly called by the
compiler as tosmula0 and tosumula0 resp.


git-svn-id: svn://svn.cc65.org/cc65/trunk@4036 b7a2c559-68d2-44c3-8de9-860c34a00d81
2009-08-17 20:48:28 +00:00

64 lines
1.5 KiB
ArmAsm

;
; Ullrich von Bassewitz, 2009-08-17
;
; CC65 runtime: multiplication for ints. Short versions.
;
.export tosumula0, tosmula0
.export mul8x16, mul8x16a
.import popsreg
.importzp sreg, ptr4
;---------------------------------------------------------------------------
; 8x16 routine with external entry points used by the 16x16 routine in mul.s
tosmula0:
tosumula0:
sta ptr4
mul8x16:jsr popsreg ; Get left operand
lda #0 ; Clear byte 1
ldy #8 ; Number of bits
ldx sreg+1 ; Get into register for speed
beq mul8x8 ; Do 8x8 multiplication if high byte zero
mul8x16a:
sta ptr4+1 ; Clear byte 2
lsr ptr4 ; Get first bit into carry
@L0: bcc @L1
clc
adc sreg
pha
txa ; hi byte of left op
adc ptr4+1
sta ptr4+1
pla
@L1: ror ptr4+1
ror a
ror ptr4
dey
bne @L0
tax
lda ptr4 ; Load the result
rts
;---------------------------------------------------------------------------
; 8x8 multiplication routine
mul8x8:
lsr ptr4 ; Get first bit into carry
@L0: bcc @L1
clc
adc sreg
@L1: ror
ror ptr4
dey
bne @L0
tax
lda ptr4 ; Load the result
rts ; Done