;-------------------------------------------------------------------------- ; div.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 __divsuchar .globl __modsuchar .globl __divuschar .globl __moduschar .globl __divschar .globl __modschar .globl __divsint .globl __modsint .globl __divuchar .globl __moduchar .globl __divuint .globl __moduint __divsuchar: ld hl,#2+1 add hl,sp ld e,(hl) dec hl ld c,(hl) ld b,#0 call signexte ld e,c ld d,b ret __modsuchar: ld hl,#2+1 add hl,sp ld e,(hl) dec hl ld c,(hl) ld b,#0 jp signexte __divuschar: ld hl,#2+1 ld d, h add hl,sp ld e,(hl) dec hl ld c,(hl) ld a,c ; Sign extend rlca sbc a ld b,a call .div16 ld e,c ld d,b ret __moduschar: ld hl,#2+1 ld d, h add hl,sp ld e,(hl) dec hl ld c,(hl) ld a,c ; Sign extend rlca sbc a ld b,a call .div16 ret __divschar: ld hl,#2+1 add hl,sp ld e,(hl) dec hl ld l,(hl) ld c,l call .div8 ld e,c ld d,b ret __modschar: ld hl,#2+1 add hl,sp ld e,(hl) dec hl ld l,(hl) ld c,l call .div8 ;; Already in DE ret __divsint: ld hl,#2+3 add hl,sp ld d,(hl) dec hl ld e,(hl) dec hl ld a,(hl) dec hl ld l,(hl) ld h,a ld b,h ld c,l call .div16 ld e,c ld d,b ret __modsint: ld hl,#2+3 add hl,sp ld d,(hl) dec hl ld e,(hl) dec hl ld a,(hl) dec hl ld l,(hl) ld h,a ld b,h ld c,l call .div16 ;; Already in DE ret ;; Unsigned __divuchar: ld hl,#2+1 add hl,sp ld e,(hl) dec hl ld l,(hl) ld c,l call .divu8 ld e,c ld d,b ret __moduchar: ld hl,#2+1 add hl,sp ld e,(hl) dec hl ld l,(hl) ld c,l call .divu8 ;; Already in DE ret __divuint: ld hl,#2+3 add hl,sp ld d,(hl) dec hl ld e,(hl) dec hl ld a,(hl) dec hl ld l,(hl) ld h,a ld b,h ld c,l call .divu16 ld e,c ld d,b ret __moduint: ld hl,#2+3 add hl,sp ld d,(hl) dec hl ld e,(hl) dec hl ld a,(hl) dec hl ld l,(hl) ld h,a ld b,h ld c,l call .divu16 ;; Already in DE ret .div8:: .mod8:: ld a,c ; Sign extend rlca sbc a ld b,a signexte: ld a,e ; Sign extend rlca sbc a ld d,a ; Fall through to .div16 ;; 16-bit division ;; ;; Entry conditions ;; BC = dividend ;; DE = divisor ;; ;; Exit conditions ;; BC = quotient ;; DE = remainder ;; If divisor is non-zero, carry=0 ;; If divisor is 0, carry=1 and both quotient and remainder are 0 ;; ;; Register used: AF,BC,DE,HL .div16:: .mod16:: ;; 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,b ; Get high byte of dividend push af ; Save as sign of remainder xor d ; Xor with high byte of divisor push af ; Save sign of quotient ;; Take absolute value of divisor bit 7,d jr Z,.chkde ; Jump if divisor is positive sub a ; Substract divisor from 0 sub e ld e,a sbc a ; Propagate borrow (A=0xFF if borrow) sub d ld d,a ;; Take absolute value of dividend .chkde: bit 7,b jr Z,.dodiv ; Jump if dividend is positive sub a ; Substract dividend from 0 sub c ld c,a sbc a ; Propagate borrow (A=0xFF if borrow) sub b ld b,a ;; Divide absolute values .dodiv: call .divu16 jr C,.exit ; Exit if divide by zero ;; Negate quotient if it is negative pop af ; recover sign of quotient and #0x80 jr Z,.dorem ; Jump if quotient is positive sub a ; Substract quotient from 0 sub c ld c,a sbc a ; Propagate borrow (A=0xFF if borrow) sub b ld b,a .dorem: ;; Negate remainder if it is negative pop af ; recover sign of remainder and #0x80 ret Z ; Return if remainder is positive sub a ; Substract remainder from 0 sub e ld e,a sbc a ; Propagate remainder (A=0xFF if borrow) sub d ld d,a ret .exit: pop af pop af ret .divu8:: .modu8:: ld b,#0x00 ld d,b ; Fall through to divu16 .divu16:: .modu16:: ;; Check for division by zero ld a,e or d jr NZ,.divide ; Branch if divisor is non-zero ld bc,#0x00 ; Divide by zero error ld d,b ld e,c scf ; Set carry, invalid result ret .divide: ld l,c ; L = low byte of dividend/quotient ld h,b ; H = high byte of dividend/quotient ld bc,#0x00 ; BC = remainder or a ; Clear carry to start ld a,#16 ; 16 bits in dividend .dvloop: ;; Shift next bit of quotient into bit 0 of dividend ;; Shift next MSB of dividend into LSB of remainder ;; BC holds both dividend and quotient. While we shift a bit from ;; MSB of dividend, we shift next bit of quotient in from carry ;; HL holds remainder ;; Do a 32-bit left shift, shifting carry to L, L to H, ;; H to C, C to B push af ; save number of bits remaining rl l ; Carry (next bit of quotient) to bit 0 rl h ; Shift remaining bytes rl c rl b ; Clears carry since BC was 0 ;; If remainder is >= divisor, next bit of quotient is 1. This ;; bit goes to carry push bc ; Save current remainder ld a,c ; Substract divisor from remainder sbc e ld c,a ld a,b sbc d ld b,a ccf ; Complement borrow so 1 indicates a ; successful substraction (this is the ; next bit of quotient) jr C,.drop ; Jump if remainder is >= dividend pop bc ; Otherwise, restore remainder pop af ; recover # bits remaining, carry flag destroyed dec a or a ; restore (clear) the carry flag jr NZ,.dvloop jr .nodrop .drop: inc sp inc sp pop af ; recover # bits remaining, carry flag destroyed dec a scf ; restore (set) the carry flag jr NZ,.dvloop jr .nodrop .nodrop: ;; Shift last carry bit into quotient ld d,b ; DE = remainder ld e,c rl l ; Carry to L ld c,l ; C = low byte of quotient rl h ld b,h ; B = high byte of quotient or a ; Clear carry, valid result ret