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1 // Copyright 2018 The Go Authors. All rights reserved. |
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2 // Use of this source code is governed by a BSD-style |
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3 // license that can be found in the LICENSE file. |
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4 |
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5 // +build !purego,!appengine |
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6 |
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7 package strs |
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8 |
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9 import ( |
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10 "unsafe" |
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11 |
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12 pref "google.golang.org/protobuf/reflect/protoreflect" |
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13 ) |
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14 |
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15 type ( |
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16 stringHeader struct { |
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17 Data unsafe.Pointer |
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18 Len int |
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19 } |
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20 sliceHeader struct { |
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21 Data unsafe.Pointer |
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22 Len int |
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23 Cap int |
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24 } |
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25 ) |
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26 |
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27 // UnsafeString returns an unsafe string reference of b. |
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28 // The caller must treat the input slice as immutable. |
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29 // |
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30 // WARNING: Use carefully. The returned result must not leak to the end user |
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31 // unless the input slice is provably immutable. |
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32 func UnsafeString(b []byte) (s string) { |
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33 src := (*sliceHeader)(unsafe.Pointer(&b)) |
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34 dst := (*stringHeader)(unsafe.Pointer(&s)) |
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35 dst.Data = src.Data |
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36 dst.Len = src.Len |
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37 return s |
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38 } |
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39 |
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40 // UnsafeBytes returns an unsafe bytes slice reference of s. |
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41 // The caller must treat returned slice as immutable. |
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42 // |
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43 // WARNING: Use carefully. The returned result must not leak to the end user. |
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44 func UnsafeBytes(s string) (b []byte) { |
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45 src := (*stringHeader)(unsafe.Pointer(&s)) |
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46 dst := (*sliceHeader)(unsafe.Pointer(&b)) |
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47 dst.Data = src.Data |
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48 dst.Len = src.Len |
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49 dst.Cap = src.Len |
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50 return b |
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51 } |
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52 |
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53 // Builder builds a set of strings with shared lifetime. |
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54 // This differs from strings.Builder, which is for building a single string. |
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55 type Builder struct { |
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56 buf []byte |
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57 } |
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58 |
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59 // AppendFullName is equivalent to protoreflect.FullName.Append, |
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60 // but optimized for large batches where each name has a shared lifetime. |
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61 func (sb *Builder) AppendFullName(prefix pref.FullName, name pref.Name) pref.FullName { |
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62 n := len(prefix) + len(".") + len(name) |
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63 if len(prefix) == 0 { |
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64 n -= len(".") |
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65 } |
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66 sb.grow(n) |
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67 sb.buf = append(sb.buf, prefix...) |
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68 sb.buf = append(sb.buf, '.') |
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69 sb.buf = append(sb.buf, name...) |
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70 return pref.FullName(sb.last(n)) |
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71 } |
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72 |
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73 // MakeString is equivalent to string(b), but optimized for large batches |
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74 // with a shared lifetime. |
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75 func (sb *Builder) MakeString(b []byte) string { |
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76 sb.grow(len(b)) |
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77 sb.buf = append(sb.buf, b...) |
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78 return sb.last(len(b)) |
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79 } |
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80 |
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81 func (sb *Builder) grow(n int) { |
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82 if cap(sb.buf)-len(sb.buf) >= n { |
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83 return |
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84 } |
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85 |
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86 // Unlike strings.Builder, we do not need to copy over the contents |
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87 // of the old buffer since our builder provides no API for |
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88 // retrieving previously created strings. |
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89 sb.buf = make([]byte, 2*(cap(sb.buf)+n)) |
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90 } |
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91 |
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92 func (sb *Builder) last(n int) string { |
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93 return UnsafeString(sb.buf[len(sb.buf)-n:]) |
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94 } |