github.com/m3db/m3@v1.5.0/src/dbnode/x/xio/reader64.go (about)

     1  // Copyright (c) 2020 Uber Technologies, Inc.
     2  //
     3  // Permission is hereby granted, free of charge, to any person obtaining a copy
     4  // of this software and associated documentation files (the "Software"), to deal
     5  // in the Software without restriction, including without limitation the rights
     6  // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
     7  // copies of the Software, and to permit persons to whom the Software is
     8  // furnished to do so, subject to the following conditions:
     9  //
    10  // The above copyright notice and this permission notice shall be included in
    11  // all copies or substantial portions of the Software.
    12  //
    13  // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
    14  // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
    15  // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
    16  // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
    17  // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
    18  // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
    19  // THE SOFTWARE.
    20  
    21  package xio
    22  
    23  import (
    24  	"encoding/binary"
    25  	"io"
    26  )
    27  
    28  // BytesReader64 implements a Reader64 over a slice of bytes.
    29  type BytesReader64 struct {
    30  	data  []byte
    31  	index int
    32  }
    33  
    34  // NewBytesReader64 creates a new BytesReader64.
    35  func NewBytesReader64(data []byte) *BytesReader64 {
    36  	return &BytesReader64{data: data}
    37  }
    38  
    39  // Read64 reads and returns a 64 bit word plus a number of bytes (up to 8) actually read.
    40  func (r *BytesReader64) Read64() (word uint64, n byte, err error) {
    41  	if r.index+8 <= len(r.data) {
    42  		// NB: this compiles to a single 64 bit load followed by
    43  		// a BSWAPQ on amd64 gc 1.13 (https://godbolt.org/z/oTK1jx).
    44  		res := binary.BigEndian.Uint64(r.data[r.index:])
    45  		r.index += 8
    46  		return res, 8, nil
    47  	}
    48  	if r.index >= len(r.data) {
    49  		return 0, 0, io.EOF
    50  	}
    51  	var res uint64
    52  	var bytes byte
    53  	for ; r.index < len(r.data); r.index++ {
    54  		res = (res << 8) | uint64(r.data[r.index])
    55  		bytes++
    56  	}
    57  	return res << (64 - 8*bytes), bytes, nil
    58  }
    59  
    60  // Peek64 peeks and returns the next 64 bit word plus a number of bytes (up to 8) available.
    61  func (r *BytesReader64) Peek64() (word uint64, n byte, err error) {
    62  	if r.index+8 <= len(r.data) {
    63  		// NB: this compiles to a single 64 bit load followed by
    64  		// BSWAPQ on amd64 gc 1.13 (https://godbolt.org/z/oTK1jx).
    65  		res := binary.BigEndian.Uint64(r.data[r.index:])
    66  		return res, 8, nil
    67  	}
    68  
    69  	if r.index >= len(r.data) {
    70  		return 0, 0, io.EOF
    71  	}
    72  
    73  	var res uint64
    74  	var bytes byte
    75  	for i := r.index; i < len(r.data); i++ {
    76  		res = (res << 8) | uint64(r.data[i])
    77  		bytes++
    78  	}
    79  	return res << (64 - 8*bytes), bytes, nil
    80  }
    81  
    82  // Reset resets the BytesReader64 for reuse.
    83  func (r *BytesReader64) Reset(data []byte) {
    84  	r.data = data
    85  	r.index = 0
    86  }