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// 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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//go:build !purego && !appengine |
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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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"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 protoreflect.FullName, name protoreflect.Name) protoreflect.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 protoreflect.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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} |