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; SPDX-FileCopyrightText: 2025 Leo Marušić <leomarusic7@gmail.com>
; SPDX-License-Identifier: MIT
MAIN:
MOV SP, #0x10000 ; stack initialization
LDR R0, MEM ; pointer to the address of the operands
LDR R12, REZ ; pointer for the result address
MAINLOOP:
ADD R0, R0, #0x8 ; point to the operation in the operand block
LDR R1, [R0] ; save the operation code in R1
CMP R1, #0x0 ; check for subtraction
BEQ SUBTRACT
CMP R1, #0x1 ; check for addition
BEQ ADDLOOP
CMP R1, #0x2 ; check for multiplication
BEQ MULLOOP
CMP R1, #0x3 ; check for division
BEQ DIVIDEOP
MVN R2, #0x0 ; put 0xFFFFFFFF in R2
CMP R1, R2 ; check for the end
BEQ FINISH
B MAINLOOP ; go back to the loop
SUBTRACT:
SUB R0, R0, #0x8 ; go back to the beginning of the operand block
LDR R1, [R0] ; load the first operand
LDR R2, [R0, #0x4] ; load the second operand
SUB R3, R1, R2 ; subtract
STR R3, [R12] ; save the result
ADD R12, R12, #0x4 ; move the result address pointer
ADD R0, R0, #0xC ; move the operand address pointer
B MAINLOOP
ADDLOOP:
SUB R0, R0, #0x8 ; go back to the beginning of the operand block
LDR R1, [R0] ; load the first operand
LDR R2, [R0, #0x4] ; load the second operand
ADD R3, R1, R2 ; add
STR R3, [R12] ; save the result
ADD R12, R12, #0x4 ; move the result address pointer
ADD R0, R0, #0xC ; move the operand address pointer
B MAINLOOP
MULLOOP:
SUB R0, R0, #0x8 ; go back to the beginning of the operand block
LDR R1, [R0] ; load the first operand
LDR R2, [R0, #0x4] ; load the second operand
MUL R3, R1, R2 ; multiply
STR R3, [R12] ; save the result
ADD R12, R12, #0x4 ; move the result address pointer
ADD R0, R0, #0xC ; move the operand address pointer
B MAINLOOP
DIVIDEOP:
SUB R0, R0, #0x8 ; go back to the beginning of the operand block
LDR R1, [R0] ; load the first operand
LDR R2, [R0, #0x4] ; load the second operand
SUB SP, SP, #0x4 ; space for the result
STMFD SP!, {R1-R2} ; put the operands on the stack
BL DIVIDE
ADD SP, SP, #0x8 ; stack cleanup
LDMFD SP!, {R3} ; retrieve the result
STR R3, [R12] ; save the result
ADD R12, R12, #0x4 ; move the result address pointer
ADD R0, R0, #0xC ; move the operand address pointer
B MAINLOOP
DIVIDE:
STMFD SP!, {R3-R5} ; save the context
LDR R3, [SP, #12] ; load the numerator
LDR R4, [SP, #16] ; load the denominator
MOV R5, #0 ; quotient
CMP R4, #0x0 ; check for division by zero
BEQ ZERO
CMP R3, #0 ; check if the numerator is negative
MVNLT R3, R3 ; 1's complement
ADDLT R3, R3, #1 ; 2's complement
CMP R4, #0 ; check if the denominator is negative
MVNLT R4, R4 ; 1's complement
ADDLT R4, R4 , #1 ; 2's complement
LOOP1:
CMP R3, R4 ; compare the numerator and the denominator
BLT DONE ; if the numerator is less than the denominator, the division is finished
SUB R3, R3, R4 ; subtract the denominator from the numerator
ADD R5, R5, #1 ; increment the quotient
B LOOP1
DONE:
CMP R1, #0 ; check the sign of the original numerator
MVNLT R5, R5 ; 1's complement the quotient
ADDLT R5, R5, #1 ; 2's complement the quotient
CMP R2, #0 ; check the sign of the original denominator
MVNLT R5, R5 ; 1's complement the quotient
ADDLT R5, R5 , #1 ; 2's complement the quotient
STR R5, [SP, #20] ; put the result on the stack
LDMFD SP!, {R3-R5} ; restore the context
MOV PC, LR
ZERO:
STR R5, [SP, #20] ; save zero as the result on the stack
LDMFD SP!, {R3-R5} ; restore the context
MOV PC, LR
FINISH:
MVN R11, #0x0 ; marker for the end of the output
STR R11, [R12] ; save the marker at the end of the output
SWI 0x123456
MEM: DW 0x600 ; Memory for the operands
ORG 0x600
DW 0xFFFFFEFF
DW 0x00000010
DW 0x00000003
DW 0x000001F4
DW 0xFFFFFD44
DW 0x00000000
DW 0x00000003
DW 0xFFFFFFEC
DW 0x00000001
DW 0xFFFFFFFE
DW 0x0000000A
DW 0x00000002
DW 0xFFFFF000
DW 0xFFFFFFC0
DW 0x00000003
DW 0x00000001
DW 0x00000004
DW 0xFFFFFFFF
RES: DW 0x2000 ; memory for the result
ORG 0x2000
DW 0x0000
DW 0x0000
DW 0x0000
DW 0x0000
DW 0x0000
DW 0x0000
DW 0x0000
DW 0x0000
DW 0x0000
DW 0x0000
DW 0x0000
DW 0x0000
DW 0x0000
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