Unstructured Embeddable Scripting VM for a toy game engine, 15 minutes in...

trinket.cpp

#include <cstdio>
#include <cstdint>
#include <cstdlib>
#include "glm/glm.hpp"
#include "glm/gtx/type_aligned.hpp"

namespace Trinket {

	enum class OP : uint8_t {
		NOOP,
		
		PUSH32_FROM_ADDR,
		POP32_TO_ADDR,

		ADD_F32,

		EXIT,
	};

	typedef int32_t Address;

	union Slot32 {
		int32_t ival;
		float fval;
		Address aval;
	};

	typedef glm::aligned_vec4 Slot128;

	class VirtualMachine {
	private:

		Slot32 ram[1024 * 1024];
		Slot32 stack[128];
		Slot128 vstack[128];

	public:

		inline Slot32* GetPtr32(Address addr) {
			// todo: bounds check
			return &ram[addr];
		}

		void Execute(uint8_t* instructions, int nbytes) {

			auto ps = stack;
			auto pv = vstack;
			auto pc = instructions;
			auto pend = instructions + nbytes;
			while (pc < pend) {
				auto op = (OP) *pc;
				++pc;
				switch(op) {
				default: 
				case OP::NOOP:
					break;
				case OP::PUSH32_FROM_ADDR:
					// todo: stack bounds check
					// todo: instruction bounds check
					// todo: ram bounds check
					*ps = ram[*(Address*)pc];
					++ps;
					pc += sizeof(Address);
					break;
				case OP::POP32_TO_ADDR: 
					// todo: stack bounds check
					// todo: instruction bounds check
					// todo: ram bounds check
					ram[*(Address*)pc] = *(ps-1);
					--ps;
					pc += sizeof(Address);
					break;
				case OP::ADD_F32: 
					// todo: stack bounds check
					(ps-2)->fval += (ps-1)->fval;
					--ps;
					break;
				case OP::EXIT:
					pc = pend;
					break;
				}
			}


		}

	};

}

int main(int argc, char * argv[]) {
	puts("Hello, World");
	using namespace Trinket;
	static VirtualMachine vm;
	vm.GetPtr32(1)->fval = 20.0f;
	vm.GetPtr32(2)->fval = 22.0f;
	static uint8_t instructions[] = {
		(uint8_t) OP::PUSH32_FROM_ADDR, 1, 0, 0, 0,
		(uint8_t) OP::PUSH32_FROM_ADDR, 2, 0, 0, 0,
		(uint8_t) OP::ADD_F32,
		(uint8_t) OP::POP32_TO_ADDR, 3, 0, 0, 0,
		(uint8_t) OP::EXIT,
	};
	vm.Execute(instructions, sizeof(instructions));
	printf("Result = %f\n", vm.GetPtr32(3)->fval);
	return 0;
}