miden_field/
utils.rs

1use alloc::string::String;
2use core::fmt::Write;
3
4use thiserror::Error;
5
6/// Renders an array of bytes as hex into a String.
7pub fn bytes_to_hex_string<const N: usize>(data: [u8; N]) -> String {
8    let mut s = String::with_capacity(N + 2);
9
10    s.push_str("0x");
11    for byte in data.iter() {
12        write!(s, "{byte:02x}").expect("formatting hex failed");
13    }
14
15    s
16}
17
18/// Defines errors which can occur during parsing of hexadecimal strings.
19#[derive(Debug, Error)]
20pub enum HexParseError {
21    #[error("expected hex data to have length {expected}, including the 0x prefix, found {actual}")]
22    InvalidLength { expected: usize, actual: usize },
23    #[error("hex encoded data must start with 0x prefix")]
24    MissingPrefix,
25    #[error("hex encoded data must contain only characters [0-9a-fA-F]")]
26    InvalidChar,
27    #[error("hex encoded values of a Digest must be inside the field modulus")]
28    OutOfRange,
29}
30
31/// Parses a hex string into an array of bytes of known size.
32pub fn hex_to_bytes<const N: usize>(value: &str) -> Result<[u8; N], HexParseError> {
33    let expected: usize = (N * 2) + 2;
34    if value.len() != expected {
35        return Err(HexParseError::InvalidLength { expected, actual: value.len() });
36    }
37
38    if !value.starts_with("0x") {
39        return Err(HexParseError::MissingPrefix);
40    }
41
42    let mut data = value.bytes().skip(2).map(|v| match v {
43        b'0'..=b'9' => Ok(v - b'0'),
44        b'a'..=b'f' => Ok(v - b'a' + 10),
45        b'A'..=b'F' => Ok(v - b'A' + 10),
46        _ => Err(HexParseError::InvalidChar),
47    });
48
49    let mut decoded = [0u8; N];
50    for byte in decoded.iter_mut() {
51        // These `unwrap` calls are okay because the length was checked above
52        let high: u8 = data.next().unwrap()?;
53        let low: u8 = data.next().unwrap()?;
54        *byte = (high << 4) + low;
55    }
56
57    Ok(decoded)
58}
miden_field/utils.rs

miden_field/
utils.rs
