zeroshade commented on a change in pull request #9671: URL: https://github.com/apache/arrow/pull/9671#discussion_r597156540
########## File path: go/parquet/internal/utils/bit_reader.go ########## @@ -0,0 +1,344 @@ +// 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. + +package utils + +import ( + "encoding/binary" + "errors" + "io" + "math" + "reflect" + "unsafe" + + "github.com/apache/arrow/go/arrow" + "github.com/apache/arrow/go/arrow/bitutil" + "github.com/apache/arrow/go/arrow/memory" +) + +// masks for grabbing the trailing bits based on the number of trailing bits desired +var trailingMask [64]uint64 + +func init() { + // generate the masks at init so we don't have to hard code them. + for i := 0; i < 64; i++ { + trailingMask[i] = (math.MaxUint64 >> (64 - i)) + } +} + +// trailingBits returns a value constructed from the bits trailing bits of +// the value v that is passed in. If bits >= 64, then we just return v. +func trailingBits(v uint64, bits uint) uint64 { + if bits >= 64 { + return v + } + return v & trailingMask[bits] +} + +// reader is a useful interface to define the functionality we need for implementation +type reader interface { + io.Reader + io.ReaderAt + io.Seeker +} + +// default buffer length +const buflen = 1024 + +// BitReader implements functionality for reading bits or bytes buffering up to a uint64 +// at a time from the reader in order to improve efficiency. It also provides +// methods to read multiple bytes in one read such as encoded ints/values. +// +// This BitReader is the basis for the other utility classes like RLE decoding +// and such, providing the necessary functions for interpreting the values. +type BitReader struct { + reader reader + buffer uint64 + byteoffset int64 + bitoffset uint + raw [8]byte + + unpackBuf [buflen]uint32 +} + +// NewBitReader takes in a reader that implements io.Reader, io.ReaderAt and io.Seeker +// interfaces and returns a BitReader for use with various bit level manipulations. +func NewBitReader(r reader) *BitReader { + return &BitReader{reader: r} +} + +// CurOffset returns the current Byte offset into the data that the reader is at. +func (b *BitReader) CurOffset() int64 { + return b.byteoffset + bitutil.BytesForBits(int64(b.bitoffset)) +} + +// Reset allows reusing a BitReader by setting a new reader and resetting the internal +// state back to zeros. +func (b *BitReader) Reset(r reader) { + b.reader = r + b.buffer = 0 + b.byteoffset = 0 + b.bitoffset = 0 +} + +// GetVlqInt reads a Vlq encoded int from the stream. The encoded value must start +// at the beginning of a byte and this returns false if there weren't enough bytes +// in the buffer or reader. This will call `ReadByte` which in turn retrieves byte +// aligned values from the reader +func (b *BitReader) GetVlqInt() (uint64, bool) { + tmp, err := binary.ReadUvarint(b) + if err != nil { + return 0, false + } + return tmp, true +} + +// GetZigZagVlqInt reads a zigzag encoded integer, returning false if there weren't +// enough bytes remaining. +func (b *BitReader) GetZigZagVlqInt() (int64, bool) { Review comment: added -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: [email protected]
