[GitHub] [arrow-rs] viirya commented on a diff in pull request #3057: add bloom filter implementation based on split block (sbbf) spec

[GitBox <gi...@apache.org>]

viirya commented on code in PR #3057:
URL: https://github.com/apache/arrow-rs/pull/3057#discussion_r1020821926


##########
parquet/src/bloom_filter/mod.rs:
##########
@@ -0,0 +1,217 @@
+// 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.
+
+//! Bloom filter implementation specific to Parquet, as described
+//! in the [spec](https://github.com/apache/parquet-format/blob/master/BloomFilter.md)
+
+use crate::errors::ParquetError;
+use crate::file::metadata::ColumnChunkMetaData;
+use crate::format::{
+    BloomFilterAlgorithm, BloomFilterCompression, BloomFilterHash, BloomFilterHeader,
+};
+use std::hash::Hasher;
+use std::io::{Read, Seek, SeekFrom};
+use thrift::protocol::TCompactInputProtocol;
+use twox_hash::XxHash64;
+
+/// Salt as defined in the [spec](https://github.com/apache/parquet-format/blob/master/BloomFilter.md#technical-approach)
+const SALT: [u32; 8] = [
+    0x47b6137b_u32,
+    0x44974d91_u32,
+    0x8824ad5b_u32,
+    0xa2b7289d_u32,
+    0x705495c7_u32,
+    0x2df1424b_u32,
+    0x9efc4947_u32,
+    0x5c6bfb31_u32,
+];
+
+/// Each block is 256 bits, broken up into eight contiguous "words", each consisting of 32 bits.
+/// Each word is thought of as an array of bits; each bit is either "set" or "not set".
+type Block = [u32; 8];
+
+/// takes as its argument a single unsigned 32-bit integer and returns a block in which each
+/// word has exactly one bit set.
+fn mask(x: u32) -> Block {
+    let mut result = [0_u32; 8];
+    for i in 0..8 {
+        // wrapping instead of checking for overflow
+        let y = x.wrapping_mul(SALT[i]);
+        let y = y >> 27;
+        result[i] = 1 << y;
+    }
+    result
+}
+
+/// setting every bit in the block that was also set in the result from mask
+fn block_insert(block: &mut Block, hash: u32) {
+    let mask = mask(hash);
+    for i in 0..8 {
+        block[i] |= mask[i];
+    }
+}
+
+/// returns true when every bit that is set in the result of mask is also set in the block.
+fn block_check(block: &Block, hash: u32) -> bool {
+    let mask = mask(hash);
+    for i in 0..8 {
+        if block[i] & mask[i] == 0 {
+            return false;
+        }
+    }
+    true
+}
+
+/// A split block Bloom filter
+pub struct Sbbf(Vec<Block>);
+
+impl Sbbf {
+    fn new(bitset: &[u8]) -> Self {
+        let data = bitset
+            .chunks_exact(4 * 8)
+            .map(|chunk| {
+                let mut block = [0_u32; 8];
+                for (i, word) in chunk.chunks_exact(4).enumerate() {
+                    block[i] = u32::from_le_bytes(word.try_into().unwrap());
+                }
+                block
+            })
+            .collect::<Vec<Block>>();
+        Self(data)
+    }
+
+    pub fn read_from_column_chunk<R: Read + Seek>(
+        column_metadata: &ColumnChunkMetaData,
+        mut reader: &mut R,
+    ) -> Result<Self, ParquetError> {
+        let offset = column_metadata.bloom_filter_offset().ok_or_else(|| {
+            ParquetError::General("Bloom filter offset is not set".to_string())
+        })? as u64;
+        reader.seek(SeekFrom::Start(offset))?;
+        // deserialize header
+        let mut prot = TCompactInputProtocol::new(&mut reader);
+        let header = BloomFilterHeader::read_from_in_protocol(&mut prot)?;
+
+        match header.algorithm {
+            BloomFilterAlgorithm::BLOCK(_) => {
+                // this match exists to future proof the singleton algorithm enum
+            }
+        }
+        match header.compression {
+            BloomFilterCompression::UNCOMPRESSED(_) => {
+                // this match exists to future proof the singleton compression enum
+            }
+        }
+        match header.hash {
+            BloomFilterHash::XXHASH(_) => {
+                // this match exists to future proof the singleton hash enum
+            }
+        }
+        // length in bytes
+        let length: usize = header.num_bytes.try_into().map_err(|_| {
+            ParquetError::General("Bloom filter length is invalid".to_string())
+        })?;
+        let mut buffer = vec![0_u8; length];
+        reader.read_exact(&mut buffer).map_err(|e| {
+            ParquetError::General(format!("Could not read bloom filter: {}", e))
+        })?;
+        Ok(Self::new(&buffer))
+    }
+
+    #[inline]
+    fn hash_to_block_index(&self, hash: u64) -> usize {
+        // unchecked_mul is unstable, but in reality this is safe, we'd just use saturating mul
+        // but it will not saturate
+        (((hash >> 32).saturating_mul(self.0.len() as u64)) >> 32) as usize
+    }
+
+    /// Insert a hash into the filter
+    pub fn insert(&mut self, hash: u64) {
+        let block_index = self.hash_to_block_index(hash);
+        let block = &mut self.0[block_index];
+        block_insert(block, hash as u32);
+    }
+
+    /// Check if a hash is in the filter. May return
+    /// true ("false positive") for values that was never inserted
+    /// but will always return false if a hash has not been inserted.

Review Comment:
   ```suggestion
       /// Check if a hash is in the filter. May return
       /// true for values that was never inserted ("false positive") 
       /// but will always return false if a hash has not been inserted.
   ```



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