github.com/apache/arrow/go/v14@v14.0.1/internal/hashing/hash_string_go1.19.go (about)

     1  // Licensed to the Apache Software Foundation (ASF) under one
     2  // or more contributor license agreements.  See the NOTICE file
     3  // distributed with this work for additional information
     4  // regarding copyright ownership.  The ASF licenses this file
     5  // to you under the Apache License, Version 2.0 (the
     6  // "License"); you may not use this file except in compliance
     7  // with the License.  You may obtain a copy of the License at
     8  //
     9  // http://www.apache.org/licenses/LICENSE-2.0
    10  //
    11  // Unless required by applicable law or agreed to in writing, software
    12  // distributed under the License is distributed on an "AS IS" BASIS,
    13  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    14  // See the License for the specific language governing permissions and
    15  // limitations under the License.
    16  
    17  //go:build !go1.20 && !tinygo
    18  
    19  package hashing
    20  
    21  import (
    22  	"reflect"
    23  	"unsafe"
    24  )
    25  
    26  func hashString(val string, alg uint64) uint64 {
    27  	if val == "" {
    28  		return Hash([]byte{}, alg)
    29  	}
    30  	// highly efficient way to get byte slice without copy before
    31  	// the introduction of unsafe.StringData in go1.20
    32  	// (https://stackoverflow.com/questions/59209493/how-to-use-unsafe-get-a-byte-slice-from-a-string-without-memory-copy)
    33  	const MaxInt32 = 1<<31 - 1
    34  	buf := (*[MaxInt32]byte)(unsafe.Pointer((*reflect.StringHeader)(
    35  		unsafe.Pointer(&val)).Data))[: len(val)&MaxInt32 : len(val)&MaxInt32]
    36  	return Hash(buf, alg)
    37  }