datasketches 0.6.0

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.

use std::hash::Hash;

use crate::codec::SketchBytes;
use crate::codec::SketchSlice;
use crate::codec::assert::insufficient_data;
use crate::error::Error;

/// Serialization version.
pub const SERIAL_VERSION: u8 = 1;

/// Preamble longs for a sketch with zero stream weight.
pub const PREAMBLE_LONGS_EMPTY: u8 = 1;
/// Preamble longs for a sketch with positive stream weight, even if it retains no items.
pub const PREAMBLE_LONGS_NONEMPTY: u8 = 4;

/// Empty flag mask (both bits for compatibility).
pub const EMPTY_FLAG_MASK: u8 = 5;

/// Trait for serializing and deserializing frequent item values.
pub trait FrequentItemValue: Sized + Eq + Hash {
    /// Returns the size in bytes required to serialize the given item.
    fn serialize_size(item: &Self) -> usize;
    /// Serializes the item into the given byte buffer.
    fn serialize_value(&self, bytes: &mut SketchBytes);
    /// Deserializes an item from the given byte cursor.
    fn deserialize_value(cursor: &mut SketchSlice<'_>) -> Result<Self, Error>;
}

impl FrequentItemValue for String {
    fn serialize_size(item: &Self) -> usize {
        size_of::<u32>() + item.len()
    }

    fn serialize_value(&self, bytes: &mut SketchBytes) {
        let bs = self.as_bytes();
        bytes.write_u32_le(bs.len() as u32);
        bytes.write(bs);
    }

    fn deserialize_value(cursor: &mut SketchSlice<'_>) -> Result<Self, Error> {
        let len = cursor
            .read_u32_le()
            .map_err(insufficient_data("string item length"))? as usize;
        let available_bytes = cursor.remaining().len();
        if available_bytes < len {
            return Err(Error::insufficient_data_of(
                "string item payload",
                format_args!("expected {len} bytes, got {available_bytes}"),
            ));
        }
        let value = std::str::from_utf8(&cursor.remaining()[..len])
            .map(str::to_owned)
            .map_err(|_| Error::deserial("invalid UTF-8 string payload"))?;
        cursor.advance(len as u64);
        Ok(value)
    }
}

macro_rules! impl_primitive {
    ($name:ty, $read:ident, $write:ident) => {
        impl FrequentItemValue for $name {
            fn serialize_size(_item: &Self) -> usize {
                size_of::<$name>()
            }

            fn serialize_value(&self, bytes: &mut SketchBytes) {
                bytes.$write(*self);
            }

            fn deserialize_value(cursor: &mut SketchSlice<'_>) -> Result<Self, Error> {
                cursor
                    .$read()
                    .map_err(insufficient_data(concat!(stringify!($name), " item")))
            }
        }
    };
}

impl_primitive!(i64, read_i64_le, write_i64_le);
impl_primitive!(u64, read_u64_le, write_u64_le);