- ;; Originally from GBDK by Pascal Felber.
- .area _CODE
+ ;; Originally from GBDK by Pascal Felber.
-__divschar_rr_s::
+ .area _CODE
+
+__divuint_rrx_s::
+ pop af
+ pop hl
+ pop de
+ push de
+ push hl
+ push af
+
+ jr __divu16
+
+__divsuchar_rrx_s::
ld hl,#2+1
add hl,sp
-
+
ld e,(hl)
dec hl
ld l,(hl)
-
- ;; Fall through
-__divschar_rr_hds::
- ld c,l
-
- call .div8
+ xor a
+
+ jr signexte
- ld l,c
- ld h,b
-
- ret
-
-__modschar_rr_s::
+__modsuchar_rrx_s::
ld hl,#2+1
add hl,sp
-
+
ld e,(hl)
dec hl
ld l,(hl)
-
- ;; Fall through
-__modschar_rr_hds::
- ld c,l
+ xor a
- call .div8
+ call signexte
- ld l,e
- ld h,d
-
- ret
+ ex de,hl
+ ret
-__divsint_rr_s::
- ld hl,#2+3
+__divuschar_rrx_s::
+ ld hl,#2+1
+ ld d, h
add hl,sp
-
- ld d,(hl)
- dec hl
- ld e,(hl)
- dec hl
- ld a,(hl)
- dec hl
- ld l,(hl)
- ld h,a
-
- ;; Fall through
-__divsint_rr_hds::
- ld b,h
- ld c,l
-
- call .div16
- ld l,c
- ld h,b
-
- ret
-
-__modsint_rr_s::
- 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
-
- ;; Fall through
-__modsint_rr_hds::
- ld b,h
- ld c,l
- call .div16
+ ld a,l ; Sign extend
+ rlca
+ sbc a
+ ld h,a
- ld l,e
- ld h,d
-
- ret
+ jr __div16
- ;; Unsigned
-__divuchar_rr_s::
+__divschar_rrx_s::
ld hl,#2+1
add hl,sp
-
- ld e,(hl)
- dec hl
- ld l,(hl)
-
- ;; Fall through
-__divuchar_rr_hds::
- ld c,l
- call .divu8
- ld l,c
- ld h,b
-
- ret
-
-__moduchar_rr_s::
- ld hl,#2+1
- add hl,sp
-
ld e,(hl)
dec hl
ld l,(hl)
-
- ;; Fall through
-__moduchar_rr_hds::
- ld c,l
- call .divu8
- ld l,e
- ld h,d
+ ;; Fall through
+__divschar_rrx_hds::
+__div8::
+ ld a,l ; Sign extend
+ rlca
+ sbc a
+signexte:
+ ld h,a
+ ld a,e ; Sign extend
+ rlca
+ sbc a
+ ld d,a
+ ; Fall through to __div16
+
+ ;; signed 16-bit division
+ ;;
+ ;; Entry conditions
+ ;; HL = dividend
+ ;; DE = divisor
+ ;;
+ ;; Exit conditions
+ ;; HL = 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
+__divsint_rrx_hds::
+__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 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 ; Substract dividend from 0
+ sub l
+ ld l,a
+ sbc a ; Propagate borrow (A=0xFF if borrow)
+ sub h
+ ld h,a
+ ;; Take absolute value of divisor
+.chkde:
+ bit 7,d
+ jr Z,.dodiv ; 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
+ ;; 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
+ jr NC,.dorem ; Jump if quotient is positive
+ ld b,a
+ sub a ; Substract quotient from 0
+ sub l
+ ld l,a
+ sbc a ; Propagate borrow (A=0xFF if borrow)
+ sub h
+ ld h,a
+ ld a,b
+.dorem:
+ ;; Negate remainder if it is negative
+ rla
+ ret NC ; 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
+.dividebyzero:
+ ld h,d ; Divide by zero error: D=E=0
+ ld l,e
+ scf ; Set carry, invalid result
ret
-__divuint_rr_s::
- ld hl,#2+3
+ ;; Unsigned
+__divuchar_rrx_s::
+ ld hl,#2+1
add hl,sp
-
- ld d,(hl)
- dec hl
- ld e,(hl)
- dec hl
- ld a,(hl)
- dec hl
- ld l,(hl)
- ld h,a
-
- ;; Fall through
-__divuint_rr_hds::
- ld b,h
- ld c,l
- call .divu16
- ld l,c
- ld h,b
-
- ret
-
-__moduint_rr_s::
- 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
- ;; Fall through
-
-__moduint_rr_hds::
- ld b,h
- ld c,l
-
- call .divu16
- ld l,e
- ld h,d
-
- ret
-
-.div8::
-.mod8::
- LD A,C ; Sign extend
- RLCA
- SBC A
- LD B,A
- 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
- LD (.srem),A ; Save as sign of remainder
- XOR D ; Xor with high byte of divisor
- LD (.squot),A ; Save sign of quotient
- ;; Take absolute value of divisor
- BIT 7,D
- jp 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
- jp 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
- RET C ; Exit if divide by zero
- ;; Negate quotient if it is negative
- LD A,(.squot)
- AND #0x80
- jp 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
- LD A,(.srem)
- 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
-
-.divu8::
-.modu8::
- LD B,#0x00
- LD D,B
- ; Fall through to divu16
-
-.divu16::
-.modu16::
- ;; Check for division by zero
- LD A,E
- OR D
- jp 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 hl,#0
-; 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
- ex af,af
- LD A,#16 ; 16 bits in dividend
+ ;; Fall through
+__divuchar_rrx_hds::
+__divu8::
+ ld h,#0x00
+ ld d,h
+ ; Fall through to divu16
+
+ ;; unsigned 16-bit division
+ ;; Restructured on April 2009 by Marco Bodrato(http://bodrato.it/ )
+ ;;
+ ;; Entry conditions
+ ;; HL = dividend
+ ;; DE = divisor
+ ;;
+ ;; Exit conditions
+ ;; HL = 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,B,DE,HL
+__divuint_rrx_hds::
+__divu16::
+ ;; Check for division by zero
+ ld a,e
+ or d
+ jr Z,.dividebyzero ; Branch if divisor is non-zero
+ ld a,h
+ ld c,l
+ ld hl,#0
+ ;; Carry was cleared by OR, this "0" bit will pass trough AC.[*]
+ ld b,#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
- ex af,af'
- RL C ; Carry (next bit of quotient) to bit 0
- RL B ; Clears carry since BC was 0
- adc hl,hl
-
- ;; If remainder is >= divisor, next bit of quotient is 1. This
- ;; bit goes to carry
- PUSH HL ; Save current remainder
- sbc hl,de
-; 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)
- jp C,.drop ; Jump if remainder is >= dividend
- POP HL ; Otherwise, restore remainder
- jp .nodrop
-.drop:
- INC SP
- INC SP
+ ;; Cleaned up on April 2009 by Marco Bodrato(http://bodrato.it/ )
+ ;; Shift next bit of quotient into bit 0 of dividend
+ ;; Shift next MSB of dividend into LSB of remainder
+ ;; AC 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 C, C to A,
+ ;; A to HL
+ rl c ; Carry (next bit of quotient) to bit 0
+ rla
+ adc hl,hl ; HL < 32768 before, no carry, ever.
+
+ ;; If remainder is >= divisor, next bit of quotient is 1. We try
+ ;; to compute the difference.
+ sbc hl,de
+ jr NC,.nodrop ; Jump if remainder is >= dividend
+ add hl,de ; Otherwise, restore remainder
+ ;; The add above sets the carry, because sbc hl,de did set it.
.nodrop:
- ex af,af'
- DEC A ; DEC does not affect carry flag
- jp NZ,.dvloop
- ex af,af'
- ;; Shift last carry bit into quotient
- LD D,H ; DE = remainder
- LD E,L
- RL C ; Carry to L
-; LD C,L ; C = low byte of quotient
- RL B
-; LD B,H ; B = high byte of quotient
- OR A ; Clear carry, valid result
- RET
-
- .area _BSS
-
-.srem:
- .ds 0x01 ; Sign of quotient
-.squot:
- .ds 0x01 ; Sign of remainder
-.dcnt:
- .ds 0x01 ; Counter for division
+ ccf ; Complement borrow so 1 indicates a
+ ; successful substraction (this is the
+ ; next bit of quotient)
+ djnz .dvloop
+ ;; Shift last carry bit into quotient
+ rl c ; Carry to C
+ rla
+ ;; Carry now contains the same value it contained before
+ ;; entering .dvloop[*]: "0" = valid result.
+ ld d,a
+ ld e,c ; DE = quotient, HL = remainder
+ ex de,hl ; HL = quotient, DE = remainder
+ ret
projects / fw / sdcc / blobdiff