datasketches 0.5.0

A software library of stochastic streaming algorithms (a.k.a. sketches)
Documentation 
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// Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements.  See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership.  The ASF licenses this file
// to you under the Apache License, Version 2.0 (the
// "License"); you may not use this file except in compliance
// with the License.  You may obtain a copy of the License at
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an
// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied.  See the License for the
// specific language governing permissions and limitations
// under the License.

//! REQ sketch wire format — constants and helpers shared by sketch + compactor serdes.

use crate::codec::assert::ensure_preamble_longs_in;
use crate::codec::assert::ensure_serial_version_is;
use crate::error::Error;
use crate::req::INITIAL_SECTIONS_PER_COMPACTOR;
use crate::req::MIN_K;
use crate::req::nearest_even_section_size;

pub const SERIAL_VERSION: u8 = 1;
pub const PREAMBLE_INTS_EXACT: u8 = 2;
pub const PREAMBLE_INTS_ESTIMATION: u8 = 4;
pub const RAW_ITEMS_THRESHOLD: u64 = 4;

/// Flag bits — match the C++ enum order: RESERVED1, RESERVED2, IS_EMPTY, IS_HIGH_RANK, RAW_ITEMS,
/// IS_LEVEL_ZERO_SORTED.
pub const FLAG_IS_EMPTY: u8 = 1 << 2;
pub const FLAG_IS_HIGH_RANK: u8 = 1 << 3;
pub const FLAG_RAW_ITEMS: u8 = 1 << 4;
pub const FLAG_IS_LEVEL_ZERO_SORTED: u8 = 1 << 5;

fn section_growth_threshold(num_sections: u8) -> Option<u64> {
    num_sections
        .checked_sub(1)
        .and_then(|shift| 1u64.checked_shl(u32::from(shift)))
}

fn has_reachable_section_count(state: u64, num_sections: u8) -> bool {
    let mut sections = INITIAL_SECTIONS_PER_COMPACTOR;
    while sections < num_sections {
        let Some(threshold) = section_growth_threshold(sections) else {
            return false;
        };
        if state < threshold {
            return false;
        }
        let Some(next) = sections.checked_mul(2) else {
            return false;
        };
        sections = next;
    }
    sections == num_sections
}

pub fn validate_compactor_state(
    k: u16,
    expected_lg_weight: u8,
    state: u64,
    section_size_raw: f32,
    lg_weight: u8,
    num_sections: u8,
) -> Result<(), Error> {
    if lg_weight != expected_lg_weight {
        return Err(Error::deserial(format!(
            "REQ compactor lg_weight {lg_weight} does not match level {expected_lg_weight}"
        )));
    }
    let section_size = nearest_even_section_size(section_size_raw);
    if !section_size_raw.is_finite()
        || !(u32::from(MIN_K)..=u32::from(k)).contains(&section_size)
        || !has_reachable_section_count(state, num_sections)
    {
        return Err(Error::deserial(format!(
            "REQ compactor layout is invalid (k={k}, state={state}, section_size_raw={section_size_raw}, num_sections={num_sections})"
        )));
    }
    Ok(())
}

pub fn check_serial_version(actual: u8) -> Result<(), Error> {
    ensure_serial_version_is(SERIAL_VERSION, actual)
}

pub fn check_preamble_ints(actual: u8, num_levels: u8) -> Result<(), Error> {
    let expected = if num_levels > 1 {
        PREAMBLE_INTS_ESTIMATION
    } else {
        PREAMBLE_INTS_EXACT
    };
    ensure_preamble_longs_in(&[expected], actual)
}