github.com/coming-chat/gomobile@v0.0.0-20220601074111-56995f7d7aba/bind/seq/string.go (about)

     1  // Copyright 2014 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package seq
     6  
     7  import "unicode/utf16"
     8  
     9  // Based heavily on package unicode/utf16 from the Go standard library.
    10  
    11  const (
    12  	replacementChar = '\uFFFD'     // Unicode replacement character
    13  	maxRune         = '\U0010FFFF' // Maximum valid Unicode code point.
    14  )
    15  
    16  const (
    17  	// 0xd800-0xdc00 encodes the high 10 bits of a pair.
    18  	// 0xdc00-0xe000 encodes the low 10 bits of a pair.
    19  	// the value is those 20 bits plus 0x10000.
    20  	surr1 = 0xd800
    21  	surr2 = 0xdc00
    22  	surr3 = 0xe000
    23  
    24  	surrSelf = 0x10000
    25  )
    26  
    27  // UTF16Encode utf16 encodes s into chars. It returns the resulting
    28  // length in units of uint16. It is assumed that the chars slice
    29  // has enough room for the encoded string.
    30  func UTF16Encode(s string, chars []uint16) int {
    31  	n := 0
    32  	for _, v := range s {
    33  		switch {
    34  		case v < 0, surr1 <= v && v < surr3, v > maxRune:
    35  			v = replacementChar
    36  			fallthrough
    37  		case v < surrSelf:
    38  			chars[n] = uint16(v)
    39  			n += 1
    40  		default:
    41  			// surrogate pair, two uint16 values
    42  			r1, r2 := utf16.EncodeRune(v)
    43  			chars[n] = uint16(r1)
    44  			chars[n+1] = uint16(r2)
    45  			n += 2
    46  		}
    47  	}
    48  	return n
    49  }