ziskos-hints 1.1.0-alpha

Guest runtime and entrypoint for programs targeting the ZisK zkVM with the hints feature enabled
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use crate::handlers::read_field_bytes;
use crate::zisklib;

use anyhow::Result;

/// Process a `MODEXP` hint: decode the base, exponent, and modulus fields from
/// `data` and return the modular-exponentiation result as `u64` words.
#[inline]
pub fn modexp_hint(data: &[u64]) -> Result<Vec<u64>> {
    let mut pos = 0;
    let (base, base_len) = read_field_bytes(data, &mut pos)?;
    let (exp, exp_len) = read_field_bytes(data, &mut pos)?;
    let (modulus, modulus_len) = read_field_bytes(data, &mut pos)?;

    // Verify the data length matches: 3 length prefixes (8 bytes each) + field data,
    // converted to u64 words (rounded up for alignment).
    let expected_words = (24 + base_len + exp_len + modulus_len).div_ceil(8);
    if expected_words != data.len() {
        anyhow::bail!(
            "MODEXP hint data length mismatch: expected {} words, got {} words",
            expected_words,
            data.len()
        );
    }

    let mut hints = Vec::new();
    let mut result = vec![0u8; modulus_len];
    unsafe {
        zisklib::modexp_bytes_c(
            base.as_ptr(),
            base_len,
            exp.as_ptr(),
            exp_len,
            modulus.as_ptr(),
            modulus_len,
            result.as_mut_ptr(),
            &mut hints,
        );
    }

    Ok(hints)
}