use crate::buffer::Buffer;
use crate::native::ArrowNativeType;
use std::ops::Deref;
#[derive(Debug)]
pub struct ScalarBuffer<T: ArrowNativeType> {
#[allow(unused)]
buffer: Buffer,
ptr: *const T,
len: usize,
}
impl<T: ArrowNativeType> ScalarBuffer<T> {
pub fn new(buffer: Buffer, offset: usize, len: usize) -> Self {
let size = std::mem::size_of::<T>();
let offset_len = offset.checked_add(len).expect("length overflow");
let start_bytes = offset.checked_mul(size).expect("start bytes overflow");
let end_bytes = offset_len.checked_mul(size).expect("end bytes overflow");
let bytes = &buffer.as_slice()[start_bytes..end_bytes];
let (prefix, offsets, suffix) = unsafe { bytes.align_to::<T>() };
assert!(
prefix.is_empty() && suffix.is_empty(),
"buffer is not aligned to {size} byte boundary"
);
let ptr = offsets.as_ptr();
Self { buffer, ptr, len }
}
}
impl<T: ArrowNativeType> Deref for ScalarBuffer<T> {
type Target = [T];
fn deref(&self) -> &Self::Target {
unsafe { std::slice::from_raw_parts(self.ptr, self.len) }
}
}
impl<T: ArrowNativeType> AsRef<[T]> for ScalarBuffer<T> {
fn as_ref(&self) -> &[T] {
self
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test_basic() {
let expected = [0_i32, 1, 2];
let buffer = Buffer::from_iter(expected.iter().cloned());
let typed = ScalarBuffer::<i32>::new(buffer.clone(), 0, 3);
assert_eq!(*typed, expected);
let typed = ScalarBuffer::<i32>::new(buffer.clone(), 1, 2);
assert_eq!(*typed, expected[1..]);
let typed = ScalarBuffer::<i32>::new(buffer.clone(), 1, 0);
assert!(typed.is_empty());
let typed = ScalarBuffer::<i32>::new(buffer, 3, 0);
assert!(typed.is_empty());
}
#[test]
#[should_panic(expected = "buffer is not aligned to 4 byte boundary")]
fn test_unaligned() {
let expected = [0_i32, 1, 2];
let buffer = Buffer::from_iter(expected.iter().cloned());
let buffer = buffer.slice(1);
ScalarBuffer::<i32>::new(buffer, 0, 2);
}
#[test]
#[should_panic(expected = "range end index 16 out of range for slice of length 12")]
fn test_length_out_of_bounds() {
let buffer = Buffer::from_iter([0_i32, 1, 2]);
ScalarBuffer::<i32>::new(buffer, 1, 3);
}
#[test]
#[should_panic(expected = "range end index 16 out of range for slice of length 12")]
fn test_offset_out_of_bounds() {
let buffer = Buffer::from_iter([0_i32, 1, 2]);
ScalarBuffer::<i32>::new(buffer, 4, 0);
}
#[test]
#[should_panic(expected = "length overflow")]
fn test_length_overflow() {
let buffer = Buffer::from_iter([0_i32, 1, 2]);
ScalarBuffer::<i32>::new(buffer, usize::MAX, 1);
}
#[test]
#[should_panic(expected = "start bytes overflow")]
fn test_start_overflow() {
let buffer = Buffer::from_iter([0_i32, 1, 2]);
ScalarBuffer::<i32>::new(buffer, usize::MAX / 4 + 1, 0);
}
#[test]
#[should_panic(expected = "end bytes overflow")]
fn test_end_overflow() {
let buffer = Buffer::from_iter([0_i32, 1, 2]);
ScalarBuffer::<i32>::new(buffer, 0, usize::MAX / 4 + 1);
}
}