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|
;--------------------------------------------------------------------------
; divsigned.s
;
; Copyright (C) 2000-2010, Michael Hope, Philipp Klaus Krause
;
; 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.
;--------------------------------------------------------------------------
.area _CODE
.globl __divsint
.globl __divschar
__divsint:
pop af
pop hl
pop de
push de
push hl
push af
jp __div16
__divschar:
ld hl, #2+1
add hl, sp
ld e, (hl)
dec hl
ld l, (hl)
__div8::
ld a, l ; Sign extend
rlca
sbc a,a
ld h, a
__div_signexte::
ld a, e ; Sign extend
rlca
sbc a,a
ld d, a
; Fall through to __div16
;; signed 16-bit division
;;
;; Entry conditions
;; HL = dividend
;; DE = divisor
;;
;; Exit conditions
;; HL = quotient
;; DE = remainder
;;
;; Register used: AF,B,DE,HL
__div16::
;; Determine sign of quotient by xor-ing high bytes of dividend
;; and divisor. Quotient is positive if signs are the same, negative
;; if signs are different
;; Remainder has same sign as dividend
ld a, h ; Get high byte of dividend
xor a, d ; Xor with high byte of divisor
rla ; Sign of quotient goes into the carry
ld a, h ; Get high byte of dividend
push af ; Save sign of both quotient and reminder
; Take absolute value of dividend
rla
jr NC, .chkde ; Jump if dividend is positive
sub a, a ; Substract dividend from 0
sub a, l
ld l, a
sbc a, a ; Propagate borrow (A=0xFF if borrow)
sub a, h
ld h, a
; Take absolute value of divisor
.chkde:
bit 7, d
jr Z, .dodiv ; Jump if divisor is positive
sub a, a ; Subtract divisor from 0
sub a, e
ld e, a
sbc a, a ; Propagate borrow (A=0xFF if borrow)
sub a, d
ld d, a
; Divide absolute values
.dodiv:
call __divu16
.fix_quotient:
; Negate quotient if it is negative
pop af ; recover sign of quotient
ret NC ; Jump if quotient is positive
ld b, a
sub a, a ; Subtract quotient from 0
sub a, l
ld l, a
sbc a, a ; Propagate borrow (A=0xFF if borrow)
sub a, h
ld h, a
ld a, b
ret
__get_remainder::
; Negate remainder if it is negative and move it into hl
rla
ex de, hl
ret NC ; Return if remainder is positive
sub a, a ; Subtract remainder from 0
sub a, l
ld l, a
sbc a, a ; Propagate remainder (A=0xFF if borrow)
sub a, h
ld h, a
ret
|
