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/* Copyright (C) 2023 Aryadev Chavali
* You may distribute and modify this code under the terms of the
* GPLv2 license. You should have received a copy of the GPLv2
* license with this file. If not, please write to:
* aryadev@aryadevchavali.com.
* Created: 2023-10-15
* Author: Aryadev Chavali
* Description: Entrypoint to program
*/
#include <stdio.h>
#include <string.h>
#include "./base.h"
typedef enum
{
OP_PUSH_BYTE = 1,
OP_PUSH_WORD,
OP_PUSH_FLOAT,
} op_t;
typedef struct
{
op_t opcode;
data_t operand;
} inst_t;
#define INST_BPUSH(BYTE) \
((inst_t){.opcode = OP_PUSH_BYTE, .operand = DBYTE(BYTE)})
#define INST_WPUSH(WORD) \
((inst_t){.opcode = OP_PUSH_WORD, .operand = DWORD(WORD)})
#define INST_FPUSH(FLOAT) \
((inst_t){.opcode = OP_PUSH_FLOAT, .operand = DFLOAT(FLOAT)})
typedef struct
{
struct Stack
{
byte *data;
word ptr, max;
} stack;
struct Program
{
inst_t *instructions;
word ptr, max;
} program;
} vm_t;
void vm_load_program(vm_t *vm, inst_t *instructions, size_t size)
{
vm->program.instructions = instructions;
vm->program.max = size;
vm->program.ptr = 0;
}
void vm_load_stack(vm_t *vm, byte *bytes, size_t size)
{
vm->stack.data = bytes;
vm->stack.max = size;
vm->stack.ptr = 0;
}
void vm_push_byte(vm_t *vm, data_t b)
{
if (vm->stack.ptr >= vm->stack.max)
// TODO: Error STACK_OVERFLOW
return;
vm->stack.data[vm->stack.ptr++] = b.as_byte;
}
void vm_push_word(vm_t *vm, data_t w)
{
if (vm->stack.ptr + WORD_SIZE >= vm->stack.max)
// TODO: Error STACK_OVERFLOW
return;
// By default store in big endian
for (size_t i = 64; i > 0; i -= 8)
{
const word mask = ((word)0b11111111) << (i - 8);
byte b = (w.as_word & mask) >> (i - 8);
printf("PUSH(%lu): pushed byte %X\n", i, b);
vm_push_byte(vm, DBYTE(b));
}
}
void vm_push_float(vm_t *vm, data_t f)
{
if (vm->stack.ptr + FLOAT_SIZE >= vm->stack.max)
// TODO: Error STACK_OVERFLOW
return;
// TODO: Make this machine independent (encode IEEE754 floats
// yourself?)
memcpy(vm->stack.data + vm->stack.ptr, &f.as_float, FLOAT_SIZE);
vm->stack.ptr += FLOAT_SIZE;
}
byte vm_pop_byte(vm_t *vm)
{
if (vm->stack.ptr == 0)
// TODO: Error STACK_UNDERFLOW
return 0;
return vm->stack.data[--vm->stack.ptr];
}
word vm_pop_word(vm_t *vm)
{
if (vm->stack.ptr < WORD_SIZE)
// TODO: Error STACK_UNDERFLOW
return 0;
word w = 0;
for (size_t i = 0; i < WORD_SIZE; ++i)
{
byte b = vm_pop_byte(vm);
printf("POP(%lu): popped byte %X\n", i, b);
w = w | ((word)b << (i * 8));
}
return w;
}
f64 vm_pop_float(vm_t *vm)
{
if (vm->stack.ptr < FLOAT_SIZE)
// TODO: Error STACK_UNDERFLOW
return 0;
f64 f = 0;
// TODO: Make this machine independent (encode IEEE754 floats
// yourself?)
memcpy(&f, vm->stack.data + vm->stack.ptr - FLOAT_SIZE, FLOAT_SIZE);
vm->stack.ptr -= FLOAT_SIZE;
return f;
}
typedef void (*push_f)(vm_t *, data_t);
void vm_execute(vm_t *vm)
{
struct Program *prog = &vm->program;
if (prog->ptr >= prog->max)
// TODO: Error (Went past end of program)
return;
inst_t instruction = prog->instructions[prog->ptr];
// NOTE: This is ballsy; I'm essentially saying I will never use the
// last 2 bits unless it's a push routine
if ((instruction.opcode & 0b11) != 0)
{
// Push routine
const push_f routines[] = {[OP_PUSH_BYTE] = vm_push_byte,
[OP_PUSH_WORD] = vm_push_word,
[OP_PUSH_FLOAT] = vm_push_float};
routines[instruction.opcode](vm, instruction.operand);
prog->ptr++;
}
else
{
// TODO: Error (Unknown opcode)
return;
}
}
#define ARR_SIZE(xs) (sizeof(xs) / sizeof(xs[0]))
int main(void)
{
byte stack_data[256];
vm_t vm = {0};
vm_load_stack(&vm, stack_data, ARR_SIZE(stack_data));
return 0;
}
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