vm.c

#include <stdarg.h>
#include <stdio.h>
#include <string.h>

#include "common.h"
#include "compiler.h"
#include "debug.h"
#include "object.h"
#include "memory.h"
#include "vm.h"
#include "memory.h"

VM vm;

static void resetStack() {
    vm.stackTop = vm.stack;
}

void initVM() {
	resetStack();
	vm.objects = NULL;

	initTable(&vm.globals);
	initTable(&vm.strings);
}

void freeVM() {
	freeTable(&vm.globals);
	freeTable(&vm.strings);
	freeObjects();
}

void push(Value value) {
	*vm.stackTop = value;
	vm.stackTop++;
}

/*
 * Pop the top of the stack.
 * There is no need for "removing" it, because it's enough to move the stack pointer
 * down one spot.
 * */
Value pop() {
	vm.stackTop--;
	return *vm.stackTop;
}

static Value peek(int distance) {
    return vm.stackTop[-1 - distance];
}

static bool isFalsey(Value value) {
	return IS_NIL(value) || (IS_BOOL(value) && !AS_BOOL(value));
}

static void concatenate() {
	ObjString* b = AS_STRING(pop());
	ObjString* a = AS_STRING(pop());

	int length = a->length + b->length;
	char* chars = ALLOCATE(char, length + 1);
	memcpy(chars, a->chars, a->length);
	memcpy(chars + a->length, b->chars, b->length);
	chars[length] = '\0';

	ObjString* result = takeString(chars, length);
	push(OBJ_VAL(result));
}

static void runtimeError(const char *format, ...) {
    va_list args;
    va_start(args, format);
    vfprintf(stderr, format, args);
    va_end(args);
    fputs("\n", stderr);

    size_t instruction = vm.ip - vm.chunk->code;
    fprintf(stderr, "[line %d] in script\n", vm.chunk->lines[instruction]);

    resetStack();
}

static InterpretResult run() {
#define READ_BYTE() (*vm.ip++)
#define READ_CONSTANT() (vm.chunk->constants.values[READ_BYTE()])
#define READ_STRING() AS_STRING(READ_CONSTANT());
#define READ_SHORT() \
    (vm.ip += 2, (uint16_t) (vm.ip[-2] << 8 | vm.ip[-1]))

#define BINARY_OP(valueType, op) \
		do { \
		    if (!IS_NUMBER(peek(0)) || !IS_NUMBER(peek(1))) { \
		        runtimeError("Operands must be numbers."); \
		        return INTERPRET_RUNTIME_ERROR; \
		    } \
			double b = AS_NUMBER(pop()); \
			double a = AS_NUMBER(pop()); \
			push(valueType(a op b)); \
		} while (false)

    for (;;) {
#ifdef DEBUG_TRACE_EXECUTION
		printf("          ");
		for (Value *slot = vm.stack; slot < vm.stackTop; slot++) {
			printf("[ ");
			printValue(*slot);
			printf(" ]");
		}
		printf("\n");
        disassembleInstruction(vm.chunk, (int) (vm.ip - vm.chunk->code));
#endif

        uint8_t instruction;

        switch (instruction = READ_BYTE()) {
            case OP_CONSTANT: {
                Value constant = READ_CONSTANT();
                push(constant);
                break;
            }
            case OP_NIL: push(NIL_VAL); break;
            case OP_TRUE: push(BOOL_VAL(true)); break;
            case OP_FALSE: push(BOOL_VAL(false)); break;
			case OP_POP: pop(); break;
			case OP_GET_LOCAL: {
				uint8_t slot = READ_BYTE();
				push(vm.stack[slot]);
				break;
			}
			case OP_SET_LOCAL: {
				uint8_t slot = READ_BYTE();
				vm.stack[slot] = peek(0);
				break;
			}
			case OP_GET_GLOBAL: {
				ObjString* name = READ_STRING();
				Value value;
				if (!tableGet(&vm.globals, name, &value)) {
					runtimeError("Undefined variable '%s'.", name->chars);
					return INTERPRET_RUNTIME_ERROR;
				}
				push(value);
				break;
			}
			case OP_DEFINE_GLOBAL: {
				ObjString* name = READ_STRING();
				tableSet(&vm.globals, name, peek(0));
				pop();
				break;
			}
			case OP_SET_GLOBAL: {
				ObjString* name = READ_STRING();
				// TODO: Supposed to be 'if (->!<-tableSet(...))'?
				if (tableSet(&vm.globals, name, peek(0))) {
					runtimeError("Undefined variable '%s'.", name->chars);
					return INTERPRET_RUNTIME_ERROR;
				}
				break;
			}
            case OP_EQUAL: {
				Value b = pop();
				Value a = pop();
				push(BOOL_VAL(valuesEqual(a, b)));
				break;
            }
            case OP_GREATER:		BINARY_OP(BOOL_VAL, >); break;
            case OP_LESS:			BINARY_OP(BOOL_VAL, <); break;
			case OP_ADD: {
				if (IS_STRING(peek(0)) && IS_STRING(peek(1))) {
					concatenate();
				} else if (IS_NUMBER(peek(0)) && IS_NUMBER(peek(1))) {
					double b = AS_NUMBER(pop());
					double a = AS_NUMBER(pop());
					push(NUMBER_VAL(a + b));
				} else {
					runtimeError("Operands must be two numbers or two strings.");
					return INTERPRET_RUNTIME_ERROR;
				}
				break;
			}
			case OP_SUBTRACT:   BINARY_OP(NUMBER_VAL, -); break;
			case OP_MULTIPLY:   BINARY_OP(NUMBER_VAL, *); break;
			case OP_DIVIDE:     BINARY_OP(NUMBER_VAL, /); break;
			case OP_NOT:
				push(BOOL_VAL(isFalsey(pop())));
				break;
			case OP_NEGATE:
				if (!IS_NUMBER(peek(0))) {
				    runtimeError("Operand must be a number.");
				    return INTERPRET_RUNTIME_ERROR;
				}

				push(NUMBER_VAL(-AS_NUMBER(pop())));
				break;
			case OP_PRINT: {
                printValue(pop());
                printf("\n");
                break;
			}
            case OP_JUMP_IF_FALSE: {
                uint16_t offset = READ_SHORT();
                if (isFalsey(peek(0))) vm.ip += offset;
                break;
            }
            case OP_JUMP: {
                uint16_t offset = READ_SHORT();
                vm.ip += offset;
                break;
            }
            case OP_LOOP: {
                uint16_t offset = READ_SHORT();
                vm.ip -= offset;
                break;
            }
            case OP_RETURN:
				// Exit interpreter
                return INTERPRET_OK;
        }
    }

#undef READ_BYTE
#undef READ_SHORT
#undef READ_CONSTANT
#undef READ_STRING
#undef BINARY_OP
}

InterpretResult interpret(const char *source) {
    Chunk chunk;
    initChunk(&chunk);
	if (!compile(source, &chunk)) {
		freeChunk(&chunk);
		return INTERPRET_COMPILE_ERROR;
	}

    vm.chunk = &chunk;
    vm.ip = vm.chunk->code;

    InterpretResult result = run();

    freeChunk(&chunk);
    return result;
}