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toy.lua
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toy.lua
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local JUMP_IF_A = 1
local MOV_A_R = 2
local MOV_R_A = 3
local ADD_R_TO_A = 4
local DECR_A = 5
local RETURN_A = 6
-- the main interpreter loop
local function interpret (bytecode, a)
local regs = {
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
}
local pc = 1
while true do
local opcode = bytecode[pc]
pc = pc + 1
if opcode == JUMP_IF_A then
local target = bytecode[pc]
pc = pc + 1
if a ~= 0 then
pc = target
end
elseif opcode == MOV_A_R then
local n = bytecode[pc]
pc = pc + 1
regs[n] = a
elseif opcode == MOV_R_A then
local n = bytecode[pc]
pc = pc + 1
a = regs[n]
elseif opcode == ADD_R_TO_A then
local n = bytecode[pc]
pc = pc + 1
a = a + regs[n]
elseif opcode == DECR_A then
a = a - 1
elseif opcode == RETURN_A then
return a
end
end
end
-- __________ Entry point __________
local function entry_point(argv)
-- the program we want to interpret
-- it computes the square of its argument
bytecode = {
MOV_A_R, 1, -- i = a
MOV_A_R, 2, -- copy of 'a'
-- 5:
MOV_R_A, 1, -- i--
DECR_A,
MOV_A_R, 1,
MOV_R_A, 3, -- res += a
ADD_R_TO_A, 2,
MOV_A_R, 3,
MOV_R_A, 1, -- if i!=0: goto 5
JUMP_IF_A, 5,
MOV_R_A, 3,
RETURN_A
}
result = interpret(bytecode, tonumber(argv[1]))
print(result)
end
-- main function
entry_point(arg)