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7c1d6e35a5
Updates #11058 Change-Id: I35e7ef9b90e83cac04ca93fd964ad00ed5b48430 Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
117 lines
3.0 KiB
Go
117 lines
3.0 KiB
Go
// Copyright (c) Tailscale Inc & AUTHORS
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// SPDX-License-Identifier: BSD-3-Clause
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// nocasemaps provides efficient functions to set and get entries in Go maps
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// keyed by a string, where the string is always lower-case.
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package nocasemaps
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import (
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"unicode"
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"unicode/utf8"
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)
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// TODO(https://github.com/golang/go/discussions/54245):
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// Define a generic Map type instead. The main reason to avoid that is because
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// there is currently no convenient API for iteration.
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// An opaque Map type would force callers to interact with the map through
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// the methods, preventing accidental interactions with the underlying map
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// without using functions in this package.
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const stackArraySize = 32
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// Get is equivalent to:
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//
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// v := m[strings.ToLower(k)]
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func Get[K ~string, V any](m map[K]V, k K) V {
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if isLowerASCII(string(k)) {
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return m[k]
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}
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var a [stackArraySize]byte
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return m[K(appendToLower(a[:0], string(k)))]
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}
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// GetOk is equivalent to:
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//
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// v, ok := m[strings.ToLower(k)]
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func GetOk[K ~string, V any](m map[K]V, k K) (V, bool) {
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if isLowerASCII(string(k)) {
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v, ok := m[k]
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return v, ok
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}
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var a [stackArraySize]byte
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v, ok := m[K(appendToLower(a[:0], string(k)))]
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return v, ok
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}
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// Set is equivalent to:
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//
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// m[strings.ToLower(k)] = v
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func Set[K ~string, V any](m map[K]V, k K, v V) {
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if isLowerASCII(string(k)) {
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m[k] = v
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return
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}
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// TODO(https://go.dev/issues/55930): This currently always allocates.
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// An optimization to the compiler and runtime could make this allocate-free
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// in the event that we are overwriting a map entry.
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//
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// Alternatively, we could use string interning.
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// See an example intern data structure, see:
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// https://github.com/go-json-experiment/json/blob/master/intern.go
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var a [stackArraySize]byte
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m[K(appendToLower(a[:0], string(k)))] = v
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}
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// Delete is equivalent to:
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//
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// delete(m, strings.ToLower(k))
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func Delete[K ~string, V any](m map[K]V, k K) {
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if isLowerASCII(string(k)) {
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delete(m, k)
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return
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}
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var a [stackArraySize]byte
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delete(m, K(appendToLower(a[:0], string(k))))
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}
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// AppendSliceElem is equivalent to:
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//
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// append(m[strings.ToLower(k)], v)
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func AppendSliceElem[K ~string, S []E, E any](m map[K]S, k K, vs ...E) {
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// if the key is already lowercased
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if isLowerASCII(string(k)) {
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m[k] = append(m[k], vs...)
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return
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}
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// if key needs to become lowercase, uses appendToLower
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var a [stackArraySize]byte
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s := appendToLower(a[:0], string(k))
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m[K(s)] = append(m[K(s)], vs...)
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}
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func isLowerASCII(s string) bool {
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for i := range len(s) {
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if c := s[i]; c >= utf8.RuneSelf || ('A' <= c && c <= 'Z') {
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return false
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}
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}
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return true
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}
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func appendToLower(b []byte, s string) []byte {
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for i := 0; i < len(s); i++ {
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switch c := s[i]; {
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case 'A' <= c && c <= 'Z':
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b = append(b, c+('a'-'A'))
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case c < utf8.RuneSelf:
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b = append(b, c)
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default:
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r, n := utf8.DecodeRuneInString(s[i:])
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b = utf8.AppendRune(b, unicode.ToLower(r))
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i += n - 1 // -1 to compensate for i++ in loop advancement
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}
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}
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return b
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}
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