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|
;--------------------------------------------------------------------------
; mul.s
;
; Copyright (C) 2000, Michael Hope
;
; This library is free software; you can redistribute it and/or modify it
; under the terms of the GNU General Public License as published by the
; Free Software Foundation; either version 2, or (at your option) any
; later version.
;
; This library is distributed in the hope that it will be useful,
; but WITHOUT ANY WARRANTY; without even the implied warranty of
; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
; GNU General Public License for more details.
;
; You should have received a copy of the GNU General Public License
; along with this library; see the file COPYING. If not, write to the
; Free Software Foundation, 51 Franklin Street, Fifth Floor, Boston,
; MA 02110-1301, USA.
;
; As a special exception, if you link this library with other files,
; some of which are compiled with SDCC, to produce an executable,
; this library does not by itself cause the resulting executable to
; be covered by the GNU General Public License. This exception does
; not however invalidate any other reasons why the executable file
; might be covered by the GNU General Public License.
;--------------------------------------------------------------------------
;; Originally from GBDK by Pascal Felber.
.area _CODE
.globl __mulsuchar
.globl __muluschar
.globl __mulschar
.globl __muluchar
.globl __mulint
; operands have different sign
__mulsuchar:
ld hl,#2+1
ld b, h
add hl,sp
ld e,(hl)
dec hl
ld c,(hl)
jr signexte
__muluschar:
ld hl,#2
ld b, h
add hl,sp
ld e,(hl)
inc hl
ld c,(hl)
jr signexte
__mulschar:
ld hl,#2
add hl,sp
ld e,(hl)
inc hl
ld l,(hl)
;; Need to sign extend before going in.
ld c,l
ld a,l
rla
sbc a,a
ld b,a
signexte:
ld a,e
rla
sbc a,a
ld d,a
jp .mul16
__muluchar:
ld hl,#2
add hl,sp
ld e,(hl)
inc hl
ld c,(hl)
;; Clear the top
xor a
ld d,a
ld b,a
jp .mul16
__mulint:
ld hl,#2
add hl,sp
ld e,(hl)
inc hl
ld d,(hl)
inc hl
ld a,(hl)
inc hl
ld h,(hl)
ld l,a
;; Parameters:
;; HL, DE (left, right irrelivent)
ld b,h
ld c,l
;; 16-bit multiplication
;;
;; Entry conditions
;; BC = multiplicand
;; DE = multiplier
;;
;; Exit conditions
;; DE = less significant word of product
;;
;; Register used: AF,BC,DE,HL
.mul16:
ld hl,#0
ld a,b
; ld c,c
ld b,#16
;; Optimise for the case when this side has 8 bits of data or
;; less. This is often the case with support address calls.
or a
jp NZ,1$
ld b,#8
ld a,c
1$:
;; Taken from z88dk, which originally borrowed from the
;; Spectrum rom.
add hl,hl
rl c
rla ;DLE 27/11/98
jp NC,2$
add hl,de
2$:
dec b
jr NZ,1$
;; Return in DE
ld e,l
ld d,h
ret
|
