Introduce and implement vec_t

A vec_t is a dynamic array, separate to a buffer.  Should make it
easier to distinguish purposes using these two data types.

lib.c

@@ -8,6 +8,12 @@
 
 #include "./lib.h"
 
+bool usable_character(char c)
+{
+  return c == '>' || c == '<' || c == '+' || c == '-' || c == '-' || c == '.' ||
+         c == ',' || c == '[' || c == ']';
+}
+
 buffer_t *buffer_init_str(const char *name, const char *str, size_t str_size)
 {
   buffer_t *buf = malloc(sizeof(*buf) + str_size + 1);
@@ -61,8 +67,34 @@ char *fread_all(FILE *fp)
   return buffer.data;
 }
 
-bool usable_character(char c)
+void vec_append(vec_t *vec, void *ptr, u64 size)
 {
-  return c == '>' || c == '<' || c == '+' || c == '-' || c == '-' || c == '.' ||
-         c == ',' || c == '[' || c == ']';
+  vec_ensure_free(vec, size);
+  memcpy(vec->data + vec->size, ptr, size);
+  vec->size += size;
+}
+
+void vec_ensure(vec_t *vec, u64 abs_size)
+{
+  if (vec->capacity < abs_size)
+  {
+    vec->capacity = MAX(vec->capacity * 2, abs_size);
+    vec->data     = realloc(vec->data, vec->capacity);
+  }
+  else if (!vec->data)
+  {
+    vec->data = calloc(1, vec->capacity);
+  }
+}
+
+void vec_ensure_free(vec_t *vec, u64 rel_size)
+{
+  vec_ensure(vec, vec->size + rel_size);
+}
+
+void vec_free(vec_t *vec)
+{
+  if (vec->data)
+    free(vec->data);
+  memset(vec, 0, sizeof(*vec));
 }

lib.h

@@ -34,4 +34,16 @@ typedef struct Buffer
 } buffer_t;
 
 buffer_t *buffer_init_str(const char *name, const char *str, size_t str_size);
+
+typedef struct
+{
+  u64 size, capacity;
+  u8 *data;
+} vec_t;
+
+void vec_append(vec_t *vec, void *ptr, u64 size);
+void vec_ensure(vec_t *vec, u64 abs_size);
+void vec_ensure_free(vec_t *vec, u64 rel_size);
+void vec_free(vec_t *vec);
+
 #endif