proxima-core 0.1.0

Foundation primitives for the proxima workspace: error, ring, arena, time, markers
Documentation 
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/// Rows of a layer that hold `cached_rows` rows and are sealed: only full blocks whose every row is at least `horizon_rows` old.
#[must_use]
pub const fn seal_target(cached_rows: usize, block_tokens: usize, horizon_rows: usize) -> usize {
    if block_tokens == 0 {
        return 0;
    }
    cached_rows.saturating_sub(horizon_rows) / block_tokens * block_tokens
}

/// Block indexes a seal call newly seals; empty when nothing new seals, and the sealed end never decreases.
#[must_use]
pub const fn sealed_blocks(
    previous_sealed_end: usize,
    cached_rows: usize,
    block_tokens: usize,
    horizon_rows: usize,
) -> core::ops::Range<usize> {
    if block_tokens == 0 {
        return 0..0;
    }
    let start = previous_sealed_end / block_tokens;
    let end = seal_target(cached_rows, block_tokens, horizon_rows) / block_tokens;
    if end > start {
        start..end
    } else {
        start..start
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn kv_decision_seal_target_worked() {
        let targets: [usize; 10] = core::array::from_fn(|rows| seal_target(rows, 4, 1));

        assert_eq!(targets, [0, 0, 0, 0, 0, 4, 4, 4, 4, 8]);
    }

    #[test]
    fn kv_decision_seal_target_edges() {
        assert_eq!(seal_target(3, 4, 0), 0);
        assert_eq!(seal_target(4, 4, 0), 4);
        assert_eq!(seal_target(8, 4, 8), 0);
        assert_eq!(seal_target(100, 0, 1), 0);
        assert_eq!(seal_target(usize::MAX, 4, 0), usize::MAX - (usize::MAX % 4));
    }

    #[test]
    fn kv_decision_sealed_blocks_is_monotone() {
        assert_eq!(sealed_blocks(4, 5, 4, 1), 1..1);
        assert_eq!(sealed_blocks(4, 9, 4, 1), 1..2);
        assert_eq!(sealed_blocks(8, 5, 4, 1), 2..2);
        assert_eq!(sealed_blocks(0, 9, 4, 1), 0..2);
        assert_eq!(sealed_blocks(0, 9, 0, 1), 0..0);
    }
}