forked from TrueCloudLab/distribution
94 lines
2.4 KiB
Go
94 lines
2.4 KiB
Go
// Copyright 2018 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// +build !purego,!appengine
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package strs
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import (
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"unsafe"
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pref "google.golang.org/protobuf/reflect/protoreflect"
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)
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type (
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stringHeader struct {
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Data unsafe.Pointer
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Len int
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}
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sliceHeader struct {
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Data unsafe.Pointer
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Len int
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Cap int
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}
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)
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// UnsafeString returns an unsafe string reference of b.
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// The caller must treat the input slice as immutable.
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//
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// WARNING: Use carefully. The returned result must not leak to the end user
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// unless the input slice is provably immutable.
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func UnsafeString(b []byte) (s string) {
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src := (*sliceHeader)(unsafe.Pointer(&b))
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dst := (*stringHeader)(unsafe.Pointer(&s))
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dst.Data = src.Data
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dst.Len = src.Len
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return s
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}
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// UnsafeBytes returns an unsafe bytes slice reference of s.
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// The caller must treat returned slice as immutable.
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//
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// WARNING: Use carefully. The returned result must not leak to the end user.
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func UnsafeBytes(s string) (b []byte) {
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src := (*stringHeader)(unsafe.Pointer(&s))
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dst := (*sliceHeader)(unsafe.Pointer(&b))
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dst.Data = src.Data
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dst.Len = src.Len
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dst.Cap = src.Len
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return b
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}
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// Builder builds a set of strings with shared lifetime.
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// This differs from strings.Builder, which is for building a single string.
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type Builder struct {
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buf []byte
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}
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// AppendFullName is equivalent to protoreflect.FullName.Append,
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// but optimized for large batches where each name has a shared lifetime.
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func (sb *Builder) AppendFullName(prefix pref.FullName, name pref.Name) pref.FullName {
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n := len(prefix) + len(".") + len(name)
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if len(prefix) == 0 {
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n -= len(".")
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}
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sb.grow(n)
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sb.buf = append(sb.buf, prefix...)
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sb.buf = append(sb.buf, '.')
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sb.buf = append(sb.buf, name...)
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return pref.FullName(sb.last(n))
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}
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// MakeString is equivalent to string(b), but optimized for large batches
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// with a shared lifetime.
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func (sb *Builder) MakeString(b []byte) string {
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sb.grow(len(b))
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sb.buf = append(sb.buf, b...)
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return sb.last(len(b))
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}
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func (sb *Builder) grow(n int) {
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if cap(sb.buf)-len(sb.buf) >= n {
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return
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}
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// Unlike strings.Builder, we do not need to copy over the contents
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// of the old buffer since our builder provides no API for
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// retrieving previously created strings.
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sb.buf = make([]byte, 2*(cap(sb.buf)+n))
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}
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func (sb *Builder) last(n int) string {
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return UnsafeString(sb.buf[len(sb.buf)-n:])
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}
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