From fe7f26256b5da63e46d3e36a8ddfe119dc9095b4 Mon Sep 17 00:00:00 2001
From: Aryadev Chavali <aryadev@aryadevchavali.com>
Date: Fri, 3 Nov 2023 19:07:10 +0000
Subject: Defined a `program` structure

Essentially a "program header", followed by a count, followed by
instructions.

Provides a stronger format for bytecode files and allows for better
bounds checking on instructions.
---
 lib/inst.c | 65 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 lib/inst.h | 22 +++++++++++++++++++++
 2 files changed, 87 insertions(+)

(limited to 'lib')

diff --git a/lib/inst.c b/lib/inst.c
index 30612d8..64fbcab 100644
--- a/lib/inst.c
+++ b/lib/inst.c
@@ -433,3 +433,68 @@ inst_t *insts_read_bytecode_file(FILE *fp, size_t *ret)
   free(darr.data);
   return instructions;
 }
+
+void prog_write_bytecode(prog_t *program, darr_t *buffer)
+{
+  // Write program header
+  darr_append_bytes(buffer, (byte *)&program->header, sizeof(program->header));
+  // Write instruction count
+  darr_append_bytes(buffer, (byte *)&program->count, sizeof(program->count));
+  // Write instructions
+  insts_write_bytecode(program->instructions, program->count, buffer);
+}
+
+void prog_append_bytecode(prog_t *program, darr_t *buffer)
+{
+  insts_write_bytecode(program->instructions, program->count, buffer);
+}
+
+prog_t *prog_read_bytecode(darr_t *buffer)
+{
+  // TODO: Error (not enough space for program header)
+  if ((buffer->available - buffer->used) < sizeof(prog_header_t))
+    return NULL;
+  // Read program header
+  prog_header_t header = {0};
+  memcpy(&header, buffer->data + buffer->used, sizeof(header));
+  buffer->used += sizeof(prog_header_t);
+  // TODO: Error (not enough space for program instruction count)
+  if ((buffer->available - buffer->used) < WORD_SIZE)
+    return NULL;
+
+  // Read instruction count
+  word count = convert_bytes_to_word(buffer->data + buffer->used);
+  buffer->used += WORD_SIZE;
+  prog_t *program = malloc(sizeof(*program) + (sizeof(inst_t) * count));
+  size_t i;
+  for (i = 0; i < count && (buffer->used < buffer->available); ++i)
+    program->instructions[i] = inst_read_bytecode(buffer);
+
+  // TODO: Error (Expected more instructions)
+  if (i < count - 1)
+  {
+    free(program);
+    return NULL;
+  }
+
+  program->header = header;
+  program->count  = count;
+
+  return program;
+}
+
+void prog_write_file(prog_t *program, FILE *fp)
+{
+  darr_t bytecode = {0};
+  prog_write_bytecode(program, &bytecode);
+  fwrite(bytecode.data, bytecode.used, 1, fp);
+  free(bytecode.data);
+}
+
+prog_t *prog_read_file(FILE *fp)
+{
+  darr_t buffer = darr_read_file(fp);
+  prog_t *p     = prog_read_bytecode(&buffer);
+  free(buffer.data);
+  return p;
+}
diff --git a/lib/inst.h b/lib/inst.h
index 3877a2b..e6225a6 100644
--- a/lib/inst.h
+++ b/lib/inst.h
@@ -188,6 +188,28 @@ inst_t *insts_read_bytecode(darr_t *, size_t *);
 void insts_write_bytecode_file(inst_t *, size_t, FILE *);
 inst_t *insts_read_bytecode_file(FILE *, size_t *);
 
+typedef struct
+{
+  word start_address;
+} prog_header_t;
+
+typedef struct
+{
+  prog_header_t header;
+  word count;
+  inst_t instructions[];
+} prog_t;
+
+// Write the entire program as bytecode
+void prog_write_bytecode(prog_t *, darr_t *);
+// Only append the instructions as bytecode
+void prog_append_bytecode(prog_t *, darr_t *);
+// Read an entire program as bytecode
+prog_t *prog_read_bytecode(darr_t *);
+
+void prog_write_file(prog_t *, FILE *);
+prog_t *prog_read_file(FILE *);
+
 #define INST_NOOP ((inst_t){0})
 #define INST_HALT ((inst_t){.opcode = OP_HALT})
 
-- 
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