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-rw-r--r--src/pkg/encoding/json/fold.go143
1 files changed, 143 insertions, 0 deletions
diff --git a/src/pkg/encoding/json/fold.go b/src/pkg/encoding/json/fold.go
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+++ b/src/pkg/encoding/json/fold.go
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+// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package json
+
+import (
+ "bytes"
+ "unicode/utf8"
+)
+
+const (
+ caseMask = ^byte(0x20) // Mask to ignore case in ASCII.
+ kelvin = '\u212a'
+ smallLongEss = '\u017f'
+)
+
+// foldFunc returns one of four different case folding equivalence
+// functions, from most general (and slow) to fastest:
+//
+// 1) bytes.EqualFold, if the key s contains any non-ASCII UTF-8
+// 2) equalFoldRight, if s contains special folding ASCII ('k', 'K', 's', 'S')
+// 3) asciiEqualFold, no special, but includes non-letters (including _)
+// 4) simpleLetterEqualFold, no specials, no non-letters.
+//
+// The letters S and K are special because they map to 3 runes, not just 2:
+// * S maps to s and to U+017F 'ſ' Latin small letter long s
+// * k maps to K and to U+212A 'K' Kelvin sign
+// See http://play.golang.org/p/tTxjOc0OGo
+//
+// The returned function is specialized for matching against s and
+// should only be given s. It's not curried for performance reasons.
+func foldFunc(s []byte) func(s, t []byte) bool {
+ nonLetter := false
+ special := false // special letter
+ for _, b := range s {
+ if b >= utf8.RuneSelf {
+ return bytes.EqualFold
+ }
+ upper := b & caseMask
+ if upper < 'A' || upper > 'Z' {
+ nonLetter = true
+ } else if upper == 'K' || upper == 'S' {
+ // See above for why these letters are special.
+ special = true
+ }
+ }
+ if special {
+ return equalFoldRight
+ }
+ if nonLetter {
+ return asciiEqualFold
+ }
+ return simpleLetterEqualFold
+}
+
+// equalFoldRight is a specialization of bytes.EqualFold when s is
+// known to be all ASCII (including punctuation), but contains an 's',
+// 'S', 'k', or 'K', requiring a Unicode fold on the bytes in t.
+// See comments on foldFunc.
+func equalFoldRight(s, t []byte) bool {
+ for _, sb := range s {
+ if len(t) == 0 {
+ return false
+ }
+ tb := t[0]
+ if tb < utf8.RuneSelf {
+ if sb != tb {
+ sbUpper := sb & caseMask
+ if 'A' <= sbUpper && sbUpper <= 'Z' {
+ if sbUpper != tb&caseMask {
+ return false
+ }
+ } else {
+ return false
+ }
+ }
+ t = t[1:]
+ continue
+ }
+ // sb is ASCII and t is not. t must be either kelvin
+ // sign or long s; sb must be s, S, k, or K.
+ tr, size := utf8.DecodeRune(t)
+ switch sb {
+ case 's', 'S':
+ if tr != smallLongEss {
+ return false
+ }
+ case 'k', 'K':
+ if tr != kelvin {
+ return false
+ }
+ default:
+ return false
+ }
+ t = t[size:]
+
+ }
+ if len(t) > 0 {
+ return false
+ }
+ return true
+}
+
+// asciiEqualFold is a specialization of bytes.EqualFold for use when
+// s is all ASCII (but may contain non-letters) and contains no
+// special-folding letters.
+// See comments on foldFunc.
+func asciiEqualFold(s, t []byte) bool {
+ if len(s) != len(t) {
+ return false
+ }
+ for i, sb := range s {
+ tb := t[i]
+ if sb == tb {
+ continue
+ }
+ if ('a' <= sb && sb <= 'z') || ('A' <= sb && sb <= 'Z') {
+ if sb&caseMask != tb&caseMask {
+ return false
+ }
+ } else {
+ return false
+ }
+ }
+ return true
+}
+
+// simpleLetterEqualFold is a specialization of bytes.EqualFold for
+// use when s is all ASCII letters (no underscores, etc) and also
+// doesn't contain 'k', 'K', 's', or 'S'.
+// See comments on foldFunc.
+func simpleLetterEqualFold(s, t []byte) bool {
+ if len(s) != len(t) {
+ return false
+ }
+ for i, b := range s {
+ if b&caseMask != t[i]&caseMask {
+ return false
+ }
+ }
+ return true
+}