vyre-libs 0.6.2

vyre Category A library ecosystem - pure-IR compositions over vyre-ops hardware primitives
Documentation 
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//! Shared FFT shape and index helpers.

/// Validate an interleaved complex FFT length and return the scalar element
/// count (`2 * n`).
///
/// # Errors
///
/// Returns an actionable error when `n < 2`, `n` is not a power of two, or the
/// interleaved scalar length overflows `u32`.
pub(super) fn validate_complex_len(n: u32, op: &str) -> Result<u32, String> {
    if n < 2 {
        return Err(format!("Fix: {op} requires n >= 2; got n={n}."));
    }
    if !n.is_power_of_two() {
        return Err(format!("Fix: {op} requires n a power of two; got n={n}."));
    }
    n.checked_mul(2)
        .ok_or_else(|| format!("Fix: {op} 2*n overflows; reduce n."))
}

/// Reverse the low `bits` bits of `value`.
#[must_use]
pub(super) fn bit_reverse(value: u32, bits: usize) -> u32 {
    let mut result = 0u32;
    let mut v = value;
    for _ in 0..bits {
        result = (result << 1) | (v & 1);
        v >>= 1;
    }
    result
}

#[cfg(test)]
mod tests {
    use super::{bit_reverse, validate_complex_len};

    #[test]
    fn validate_complex_len_rejects_invalid_shapes() {
        assert!(validate_complex_len(0, "generated_fft").is_err());
        assert!(validate_complex_len(1, "generated_fft").is_err());
        assert!(validate_complex_len(6, "generated_fft")
            .expect_err("non-power-of-two must fail")
            .contains("power of two"));
        assert!(validate_complex_len(1_u32 << 31, "generated_fft")
            .expect_err("overflowing interleaved length must fail")
            .contains("2*n overflows"));
    }

    #[test]
    fn bit_reverse_covers_three_bit_permutation() {
        let got: Vec<u32> = (0..8).map(|value| bit_reverse(value, 3)).collect();
        assert_eq!(got, vec![0, 4, 2, 6, 1, 5, 3, 7]);
    }
}