Basic C interpreter environment - retrotruestory/M1DEV GitHub Wiki

Here's how to implement a basic C interpreter environment for Magic-1:

        .cseg
        .global _init_interpreter
        .global _execute_instruction
        .global _push_stack
        .global _pop_stack

// Initialize interpreter environment
_init_interpreter:
        enter   8
        push    a
        push    b
        
        // Setup interpreter stack
        ld.16   b,#INTERP_STACK_TOP
        ld.16   a,#INTERP_STACK_SIZE
        st.16   _interp_sp,b
        
        // Initialize symbol table
        call    _init_symtab
        
        pop     b
        pop     a
        leave
        ret

// Execute single instruction
_execute_instruction:
        enter   4
        push    b
        
        ld.16   b,6(sp)    ; Load instruction pointer
        ld.8    a,(b)      ; Get opcode
        
        // Decode and execute instruction
        cmp.8   a,#OP_PUSH
        br.eq   .do_push
        cmp.8   a,#OP_ADD
        br.eq   .do_add
        // ... other opcodes ...
        
        pop     b
        leave
        ret

Create the interpreter interface:

#ifndef INTERPRETER_H
#define INTERPRETER_H

#define INTERP_STACK_SIZE  1024
#define INTERP_STACK_TOP   0x18000
#define MAX_SYMBOLS        256

// Instruction opcodes
#define OP_PUSH     0x01
#define OP_POP      0x02
#define OP_ADD      0x03
#define OP_SUB      0x04
#define OP_MUL      0x05
#define OP_DIV      0x06
#define OP_CALL     0x07
#define OP_RET      0x08

typedef struct {
    uint16_t sp;           // Stack pointer
    uint16_t bp;           // Base pointer
    uint16_t pc;           // Program counter
    uint8_t *code;         // Code segment
    uint16_t code_size;    // Code size
} interp_context;

// Function declarations
extern void init_interpreter(void);
extern int execute_instruction(interp_context *ctx);
extern int run_program(uint8_t *code, uint16_t size);

#endif

Implement the core interpreter:

#include "interpreter.h"

static uint16_t interp_sp;
static uint16_t interp_stack[INTERP_STACK_SIZE];

// Simple expression evaluator
int evaluate_expression(interp_context *ctx) {
    uint8_t opcode = ctx->code[ctx->pc];
    int val1, val2, result;
    
    switch(opcode) {
        case OP_PUSH:
            ctx->pc++;
            val1 = ctx->code[ctx->pc];
            push_stack(val1);
            break;
            
        case OP_ADD:
            val2 = pop_stack();
            val1 = pop_stack();
            result = val1 + val2;
            push_stack(result);
            break;
            
        case OP_MUL:
            val2 = pop_stack();
            val1 = pop_stack();
            result = val1 * val2;
            push_stack(result);
            break;
            
        // Add other operations
    }
    
    ctx->pc++;
    return 0;
}

// Main interpreter loop
int run_program(uint8_t *code, uint16_t size) {
    interp_context ctx;
    
    // Initialize context
    ctx.pc = 0;
    ctx.code = code;
    ctx.code_size = size;
    ctx.sp = interp_sp;
    ctx.bp = interp_sp;
    
    // Main interpretation loop
    while(ctx.pc < ctx.code_size) {
        if(evaluate_expression(&ctx) < 0) {
            return -1;  // Error
        }
    }
    
    return pop_stack(); // Return final result
}

Example usage:

#include <stdio.h>
#include "interpreter.h"

int main() {
    // Simple program: 5 + (3 * 2)
    uint8_t program[] = {
        OP_PUSH, 5,    // Push 5
        OP_PUSH, 3,    // Push 3
        OP_PUSH, 2,    // Push 2
        OP_MUL,        // Multiply
        OP_ADD,        // Add
    };
    
    // Initialize interpreter
    init_interpreter();
    
    // Run program
    int result = run_program(program, sizeof(program));
    printf("Result: %d\n", result);  // Should print 11
    
    return 0;
}

Update Makefile:

CC = clcc
AS = m1_as
CFLAGS = -O2
OBJECTS = interp_core.o interpreter.o test_interp.o

test_interp: $(OBJECTS)
    $(CC) $(CFLAGS) -o $@ $(OBJECTS)

%.o: %.s
    $(AS) -o $@ $<

%.o: %.c
    $(CC) $(CFLAGS) -c $<

clean:
    rm -f test_interp *.o

Key features:

  • Simple stack-based interpreter
  • Support for basic arithmetic operations
  • Expression evaluation
  • Error handling
  • Memory safety through VM system

This implementation provides:

  1. Basic arithmetic operations
  2. Stack management
  3. Program flow control
  4. Error checking
  5. Integration with Magic-1's memory system

You can extend it by adding:

  • More complex operations
  • Function calls
  • Variables and symbols
  • Conditional execution
  • Loops and control structures
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