static jv* jvp_array_write(jv* a, int i) {
assert(i >= 0);
jvp_array* array = jvp_array_ptr(*a);
int pos = i + jvp_array_offset(*a);
if (pos < array->alloc_length && jvp_refcnt_unshared(a->u.ptr)) {
// use existing array space
for (int j = array->length; j <= pos; j++) {
array->elements[j] = JV_NULL;
}
array->length = imax(pos + 1, array->length);
a->size = imax(i + 1, a->size);
return &array->elements[pos];
} else {
// allocate a new array
int new_length = imax(i + 1, jvp_array_length(*a));
jvp_array* new_array = jvp_array_alloc(ARRAY_SIZE_ROUND_UP(new_length));
int j;
for (j = 0; j < jvp_array_length(*a); j++) {
new_array->elements[j] =
jv_copy(array->elements[j + jvp_array_offset(*a)]);
}
for (; j < new_length; j++) {
new_array->elements[j] = JV_NULL;
}
new_array->length = new_length;
jvp_array_free(*a);
jv new_jv = {JV_KIND_ARRAY, 0, 0, new_length, {&new_array->refcnt}};
*a = new_jv;
return &new_array->elements[i];
}
}
static jv* jvp_array_write(jv_nontrivial* a, int i) {
assert(i >= 0);
jvp_array* array = jvp_array_ptr(a);
int pos = i + a->i[0];
if (pos < array->alloc_length) {
// maybe we can update it in-place
// FIXME: this "optimisation" can cause circular references
#if 0
int can_write_past_end =
array->length <= pos && /* the end of this array has never been used */
a->i[1] == array->length; /* the current slice sees the end of the array */
#endif
int can_write_past_end = 0;
if (can_write_past_end || jvp_refcnt_unshared(a)) {
// extend the array
for (int j = array->length; j <= pos; j++) {
array->elements[j] = JV_NULL;
}
array->length = imax(pos + 1, array->length);
a->i[1] = imax(pos + 1, a->i[1]);
return &array->elements[pos];
}
}
int new_length = imax(i + 1, jvp_array_length(a));
jvp_array* new_array = jvp_array_alloc(ARRAY_SIZE_ROUND_UP(new_length));
int j;
for (j = 0; j < jvp_array_length(a); j++) {
new_array->elements[j] = jv_copy(array->elements[j + a->i[0]]);
}
for (; j < new_length; j++) {
new_array->elements[j] = JV_NULL;
}
new_array->length = new_length;
jvp_array_free(a);
a->ptr = &new_array->refcnt;
a->i[0] = 0;
a->i[1] = new_length;
return &new_array->elements[i];
}
