--- /dev/null
+ ;; Originally from GBDK by Pascal Felber.
+ .area _CODE
+
+__divschar::
+ push de
+ push bc
+ push ix
+ ld ix,#0
+ add ix,sp
+
+ ld c,8(ix)
+ ld e,9(ix)
+ call .div8
+
+ ld l,c
+
+ pop ix
+ pop bc
+ pop de
+ ret
+
+__modschar::
+ push de
+ push bc
+ push ix
+ ld ix,#0
+ add ix,sp
+
+ ld c,8(ix)
+ ld e,9(ix)
+ call .div8
+
+ ld l,e
+
+ pop ix
+ pop bc
+ pop de
+ ret
+
+__divsint::
+ push de
+ push bc
+ push ix
+ ld ix,#0
+ add ix,sp
+
+ ld c,8(ix)
+ ld b,9(ix)
+ ld e,10(ix)
+ ld d,11(ix)
+ call .div16
+
+ ld l,c
+ ld h,b
+
+ pop ix
+ pop bc
+ pop de
+ ret
+
+__modsint::
+ push de
+ push bc
+ push ix
+ ld ix,#0
+ add ix,sp
+
+ ld c,8(ix)
+ ld b,9(ix)
+ ld e,10(ix)
+ ld d,11(ix)
+ call .div16
+
+ ld l,e
+ ld h,d
+
+ pop ix
+ pop bc
+ pop de
+ ret
+
+ ;; Unsigned
+__divuchar::
+ push de
+ push bc
+ push ix
+ ld ix,#0
+ add ix,sp
+
+ ld c,8(ix)
+ ld e,9(ix)
+ call .divu8
+
+ ld l,c
+
+ pop ix
+ pop bc
+ pop de
+ ret
+
+__moduchar::
+ push de
+ push bc
+ push ix
+ ld ix,#0
+ add ix,sp
+
+ ld c,8(ix)
+ ld e,9(ix)
+ call .divu8
+
+ ld l,e
+
+ pop ix
+ pop bc
+ pop de
+ ret
+
+__divuint::
+ push de
+ push bc
+ push ix
+ ld ix,#0
+ add ix,sp
+
+ ld c,8(ix)
+ ld b,9(ix)
+ ld e,10(ix)
+ ld d,11(ix)
+ call .divu16
+
+ ld l,c
+ ld h,b
+
+ pop ix
+ pop bc
+ pop de
+ ret
+
+__moduint::
+ push de
+ push bc
+ push ix
+ ld ix,#0
+ add ix,sp
+
+ ld c,8(ix)
+ ld b,9(ix)
+ ld e,10(ix)
+ ld d,11(ix)
+ call .divu16
+
+ ld l,e
+ ld h,d
+
+ pop ix
+ pop bc
+ pop de
+ 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
+ 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
+ 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
+.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
+ 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
+ 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
+.drop:
+ INC SP
+ INC SP
+.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
projects / fw / sdcc / blobdiff