- ;; Originally from GBDK by Pascal Felber.
- .area _CODE
+ ;; Originally from GBDK by Pascal Felber.
+ .area _CODE
-__divschar_rrx_s::
+__divschar_rrx_s::
ld hl,#2+1
add hl,sp
-
+
ld e,(hl)
dec hl
ld l,(hl)
-
+
;; Fall through
__divschar_rrx_hds::
ld c,l
-
+
call .div8
- ld l,c
- ld h,b
-
- ret
-
-__modschar_rrx_s::
+ ld e,c
+ ld d,b
+
+ ret
+
+__modschar_rrx_s::
ld hl,#2+1
add hl,sp
-
+
ld e,(hl)
dec hl
ld l,(hl)
-
+
;; Fall through
__modschar_rrx_hds::
ld c,l
- call .div8
+ call .div8
+
+ ;; Already in DE
- ld l,e
- ld h,d
-
- ret
+ ret
-__divsint_rrx_s::
+__divsint_rrx_s::
ld hl,#2+3
add hl,sp
-
+
ld d,(hl)
dec hl
ld e,(hl)
dec hl
ld l,(hl)
ld h,a
-
+
;; Fall through
__divsint_rrx_hds::
- ld b,h
- ld c,l
+ ld b,h
+ ld c,l
+
+ call .div16
- call .div16
+ ld e,c
+ ld d,b
+
+ ret
- ld l,c
- ld h,b
-
- ret
-
__modsint_rrx_s::
ld hl,#2+3
add hl,sp
-
+
ld d,(hl)
dec hl
ld e,(hl)
;; Fall through
__modsint_rrx_hds::
- ld b,h
- ld c,l
+ ld b,h
+ ld c,l
+
+ call .div16
- call .div16
+ ;; Already in DE
- ld l,e
- ld h,d
-
- ret
+ ret
- ;; Unsigned
-__divuchar_rrx_s::
+ ;; Unsigned
+__divuchar_rrx_s::
ld hl,#2+1
add hl,sp
-
+
ld e,(hl)
dec hl
ld l,(hl)
-
+
;; Fall through
__divuchar_rrx_hds::
ld c,l
- call .divu8
-
- ld l,c
- ld h,b
-
- ret
-
-__moduchar_rrx_s::
+ call .divu8
+
+ ld e,c
+ ld d,b
+
+ ret
+
+__moduchar_rrx_s::
ld hl,#2+1
add hl,sp
-
+
ld e,(hl)
dec hl
ld l,(hl)
-
+
;; Fall through
__moduchar_rrx_hds::
ld c,l
- call .divu8
+ call .divu8
- ld l,e
- ld h,d
+ ;; Already in DE
ret
-__divuint_rrx_s::
+__divuint_rrx_s::
ld hl,#2+3
add hl,sp
-
+
ld d,(hl)
dec hl
ld e,(hl)
;; Fall through
__divuint_rrx_hds::
- ld b,h
- ld c,l
- call .divu16
-
- ld l,c
- ld h,b
-
- ret
-
-__moduint_rrx_s::
+ ld b,h
+ ld c,l
+ call .divu16
+
+ ld e,c
+ ld d,b
+
+ ret
+
+__moduint_rrx_s::
ld hl,#2+3
add hl,sp
-
+
ld d,(hl)
dec hl
ld e,(hl)
ld l,(hl)
ld h,a
;; Fall through
-
+
__moduint_rrx_hds::
- ld b,h
- ld c,l
+ ld b,h
+ ld c,l
+
+ call .divu16
- call .divu16
+ ;; Already in DE
+
+ ret
- 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
+ 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
- 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
+ ;; 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
+ 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
- RET C ; Exit if divide by zero
- ;; Negate quotient if it is negative
- LD A,(.squot)
- 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
+ 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
- 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
+ ;; 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
+ 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
+ ;; 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
+ 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
- LD (.dcnt),A
- 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
- JR .nodrop
+ ;; 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
+ 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:
- LD A,(.dcnt)
- DEC A ; DEC does not affect carry flag
- JR NZ,.dvloop
- ;; 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
-
- .area _BSS
-
-.srem:
- .ds 0x01 ; Sign of quotient
-.squot:
- .ds 0x01 ; Sign of remainder
-.dcnt:
- .ds 0x01 ; Counter for division
+ ;; 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
projects / fw / sdcc / blobdiff