muddle/src/interpreter.c

/*
 *	Copyright (c) 2024 Scott Duensing, scott@kangaroopunch.com
 *
 *	Permission is hereby granted, free of charge, to any person obtaining a copy
 *	of this software and associated documentation files (the "Software"), to deal
 *	in the Software without restriction, including without limitation the rights
 *	to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 *	copies of the Software, and to permit persons to whom the Software is
 *	furnished to do so, subject to the following conditions:
 *
 *	The above copyright notice and this permission notice shall be included in
 *	all copies or substantial portions of the Software.
 *
 *	THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 *	IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 *	FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 *	AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 *	LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 *	OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 *	SOFTWARE.
 */


#include "stddclmr.h"

#include "interpreter.h"
#include "portme.h"
#include "messages.h"
#include "story.h"
#include "state.h"
#include "variable.h"
#include "memory.h"


void interpreterDoBranch(int32_t truth) {
	uint8_t branch  = ZPEEK(__state.pc++);
	int32_t farJump = (branch & (1 << 6)) == 0;
	int32_t onTruth = (branch & (1 << 7)) ? 1 : 0;
	uint8_t byte2   = farJump ? ZPEEK(__state.pc++) : 0;
	int16_t offset;

	if (onTruth == truth) {
		offset = (int16_t)(branch & 0x3f);
		if (farJump) {
			if (offset & (1 << 5)) offset |= 0xc0;
			offset = (offset << 8) | ((int16_t)byte2);
		}
		if (offset == 0) {
			interpreterDoReturn(0);
		} else if (offset == 1) {
			interpreterDoReturn(1);
		} else {
			__state.pc = (__state.pc + offset) - 2;
		}
	}
}


void interpreterDoReturn(uint16_t r) {
	uint8_t  storeId;

	//***TODO*** Newer versions start in a real routine, but still aren't allowed to return from it.

	if (__state.bp == 0) portDie(MSG_INT_STACK_UNDERFLOW);

#ifdef DEBUGGING
	printf("Returning: initial pc=%X, bp=%u, sp=%u\n", __state.pc, __state.bp, __state.sp);
#endif

	// Dump all locals and data pushed on stack during the routine.
	__state.sp = __state.bp;
	// Dump our copy of numLocals.
	__state.sp--;
	// Restore previous frame's base pointer.
	__state.bp = __state.stack[--__state.sp];

	// Point to start of saved program counter;
	__state.sp -= 2;
	__state.pc = ((uint32_t)__state.stack[__state.sp]) | (((uint32_t)__state.stack[__state.sp + 1]) << 16);

	// Pop the result storage location.
	storeId = (uint8_t)__state.stack[--__state.sp];

#ifdef DEBUGGING
	printf("Returning: new pc=%X, bp=%u, sp=%u\n", __state.pc, __state.bp, __state.sp);
#endif

	// Store the routine result.
	variableStore(storeId, r);
}


bool interpreterParseOperand(uint8_t opType, uint8_t operandId) {
	switch(opType) {
		// Large constant.
		case 0:
			__state.operands[operandId] = ZPEEKW(__state.pc);
			__state.pc += 2;
			return true;

		// Small constant.
		case 1:
			__state.operands[operandId] = ZPEEK(__state.pc++);
			return true;

		// Variable.
		case 2:
			__state.operands[operandId] = variableLoad(ZPEEK(__state.pc++));
			return true;
	}

	return false;
}


uint8_t interpreterParseVariableOperands(uint8_t index) {
	uint8_t operandTypes = ZPEEK(__state.pc++);
	uint8_t shifter      = 6;
	uint8_t i;
	uint8_t opType;

	for (i=0; i<4; i++) {
		opType = (operandTypes >> shifter) & 0x3;
		shifter -= 2;
		if (!interpreterParseOperand(opType, index + i)) break;
	}

	return i;
}


void interpreterRun(void) {
	uint8_t opcode;
	bool    extended;
	opcodeT op;
	bool    eight;

	while (__state.quit == 0) {
		opcode   = ZPEEK(__state.pc++);
		extended = ((opcode == 190) && (storyVersion() >= 5)) ? true : false;

		if (extended) {

			opcode = ZPEEK(__state.pc++);
			if (opcode >= (sizeof(__state.extOpcodes) / sizeof(__state.extOpcodes[0]))) portDie(MSG_INT_INVALID_EXT_OPCODE);
			__state.operandCount = interpreterParseVariableOperands(0);
			op = __state.extOpcodes[opcode];

		} else {

			if (opcode <= 127) {
				// 2OP
				__state.operandCount = 2;
				interpreterParseOperand(((opcode >> 6) & 0x1) ? 2 : 1, 0);
				interpreterParseOperand(((opcode >> 5) & 0x1) ? 2 : 1, 1);
			} else if (opcode <= 175) {
				// 1OP
				__state.operandCount = 1;
				interpreterParseOperand((opcode >> 4) & 0x3, 0);
			} else if (opcode <= 191) {
				// 0OP
				__state.operandCount = 0;
			} else if (opcode > 191) {
				// Variable Opcodes
				eight = (opcode == 236) || (opcode == 250);
				if (!eight) {
					// call_vs2 and call_vn2 take up to EIGHT arguments!
					__state.operandCount = interpreterParseVariableOperands(0);
				} else {
					__state.operandCount = interpreterParseVariableOperands(0);
					if (__state.operandCount == 4) {
						__state.operandCount += interpreterParseVariableOperands(4);
					} else {
						__state.pc++;
					}
				}
			}

			op = __state.opcodes[opcode];

		}  // extended

		if (op == 0) portDie(MSG_INT_UNIMPLEMENTED_OPCODE, extended ? "ext" : "", opcode);

#ifdef DEBUGGING
		printf("pc=%X %sopcode=%u ('%s') [", (unsigned int)__state.pc, extended ? "ext " : "", opcode, extended ? __state.extOpcodesName[opcode] : __state.opcodesName[opcode]);
		if (__state.operandCount) {
			uint8_t i;
			for (i=0; i<__state.operandCount - 1; i++)
				printf("%X,", (unsigned int)__state.operands[i]);
			printf("%X", (unsigned int)__state.operands[i]);
		}
		printf("]\n");
#endif

		op();
	}
}