alloy_eips/eip4844/
utils.rs

1//! Utilities for working with EIP-4844 field elements and implementing
2//! [`SidecarCoder`].
3//!
4//! [`SidecarCoder`]: crate::eip4844::builder::SidecarCoder
5
6use crate::eip4844::{FIELD_ELEMENT_BYTES_USIZE, USABLE_BITS_PER_FIELD_ELEMENT};
7
8/// Determine whether a slice of bytes can be contained in a field element.
9pub const fn fits_in_fe(data: &[u8]) -> bool {
10    const FIELD_ELEMENT_BYTES_USIZE_PLUS_ONE: usize = FIELD_ELEMENT_BYTES_USIZE + 1;
11
12    match data.len() {
13        FIELD_ELEMENT_BYTES_USIZE_PLUS_ONE.. => false,
14        FIELD_ELEMENT_BYTES_USIZE => data[0] & 0b1100_0000 == 0, // first two bits must be zero
15        _ => true,
16    }
17}
18
19/// Calculate the number of field elements required to store the given
20/// number of bytes.
21pub const fn minimum_fe_for_bytes(bytes: usize) -> usize {
22    (bytes * 8).div_ceil(USABLE_BITS_PER_FIELD_ELEMENT)
23}
24
25/// Calculate the number of field elements required to store the given data.
26pub const fn minimum_fe(data: &[u8]) -> usize {
27    minimum_fe_for_bytes(data.len())
28}
29
30/// A wrapper for a slice of bytes that is a whole, valid field element.
31#[derive(Clone, Copy, Debug)]
32pub struct WholeFe<'a>(&'a [u8]);
33
34impl<'a> WholeFe<'a> {
35    pub(crate) const fn new_unchecked(data: &'a [u8]) -> Self {
36        Self(data)
37    }
38
39    /// Instantiate a new `WholeFe` from a slice of bytes, if it is a valid
40    /// field element.
41    pub const fn new(data: &'a [u8]) -> Option<Self> {
42        if data.len() == FIELD_ELEMENT_BYTES_USIZE && fits_in_fe(data) {
43            Some(Self::new_unchecked(data))
44        } else {
45            None
46        }
47    }
48}
49
50impl AsRef<[u8]> for WholeFe<'_> {
51    fn as_ref(&self) -> &[u8] {
52        self.0
53    }
54}
55
56#[cfg(test)]
57mod test {
58    use crate::eip4844::{FIELD_ELEMENTS_PER_BLOB, USABLE_BYTES_PER_BLOB};
59
60    use super::*;
61    #[test]
62    fn calc_required_fe() {
63        assert_eq!(minimum_fe(&[0u8; 32]), 2);
64        assert_eq!(minimum_fe(&[0u8; 31]), 1);
65        assert_eq!(minimum_fe(&[0u8; 33]), 2);
66        assert_eq!(minimum_fe(&[0u8; 64]), 3);
67        assert_eq!(minimum_fe(&[0u8; 65]), 3);
68        assert_eq!(minimum_fe_for_bytes(USABLE_BYTES_PER_BLOB), FIELD_ELEMENTS_PER_BLOB as usize);
69    }
70
71    #[test]
72    fn calc_is_valid_field_element() {
73        assert!(fits_in_fe(&[0u8; 32]));
74        assert!(!fits_in_fe(&[0u8; 33]));
75
76        assert!(WholeFe::new(&[0u8; 32]).is_some());
77        assert!(WholeFe::new(&[0u8; 33]).is_none());
78        assert!(WholeFe::new(&[0u8; 31]).is_none());
79    }
80}
alloy_eips/eip4844/utils.rs

alloy_eips/eip4844/
utils.rs
