use tcell via porting over code from awesome-gocui

vendor/github.com/gdamore/encoding/charmap.go

@@ -0,0 +1,196 @@
+// Copyright 2015 Garrett D'Amore
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use file except in compliance with the License.
+// You may obtain a copy of the license at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package encoding
+
+import (
+	"sync"
+	"unicode/utf8"
+
+	"golang.org/x/text/encoding"
+	"golang.org/x/text/transform"
+)
+
+const (
+	// RuneError is an alias for the UTF-8 replacement rune, '\uFFFD'.
+	RuneError = '\uFFFD'
+
+	// RuneSelf is the rune below which UTF-8 and the Unicode values are
+	// identical.  Its also the limit for ASCII.
+	RuneSelf = 0x80
+
+	// ASCIISub is the ASCII substitution character.
+	ASCIISub = '\x1a'
+)
+
+// Charmap is a structure for setting up encodings for 8-bit character sets,
+// for transforming between UTF8 and that other character set.  It has some
+// ideas borrowed from golang.org/x/text/encoding/charmap, but it uses a
+// different implementation.  This implementation uses maps, and supports
+// user-defined maps.
+//
+// We do assume that a character map has a reasonable substitution character,
+// and that valid encodings are stable (exactly a 1:1 map) and stateless
+// (that is there is no shift character or anything like that.)  Hence this
+// approach will not work for many East Asian character sets.
+//
+// Measurement shows little or no measurable difference in the performance of
+// the two approaches.  The difference was down to a couple of nsec/op, and
+// no consistent pattern as to which ran faster.  With the conversion to
+// UTF-8 the code takes about 25 nsec/op.  The conversion in the reverse
+// direction takes about 100 nsec/op.  (The larger cost for conversion
+// from UTF-8 is most likely due to the need to convert the UTF-8 byte stream
+// to a rune before conversion.
+//
+type Charmap struct {
+	transform.NopResetter
+	bytes map[rune]byte
+	runes [256][]byte
+	once  sync.Once
+
+	// The map between bytes and runes.  To indicate that a specific
+	// byte value is invalid for a charcter set, use the rune
+	// utf8.RuneError.  Values that are absent from this map will
+	// be assumed to have the identity mapping -- that is the default
+	// is to assume ISO8859-1, where all 8-bit characters have the same
+	// numeric value as their Unicode runes.  (Not to be confused with
+	// the UTF-8 values, which *will* be different for non-ASCII runes.)
+	//
+	// If no values less than RuneSelf are changed (or have non-identity
+	// mappings), then the character set is assumed to be an ASCII
+	// superset, and certain assumptions and optimizations become
+	// available for ASCII bytes.
+	Map map[byte]rune
+
+	// The ReplacementChar is the byte value to use for substitution.
+	// It should normally be ASCIISub for ASCII encodings.  This may be
+	// unset (left to zero) for mappings that are strictly ASCII supersets.
+	// In that case ASCIISub will be assumed instead.
+	ReplacementChar byte
+}
+
+type cmapDecoder struct {
+	transform.NopResetter
+	runes [256][]byte
+}
+
+type cmapEncoder struct {
+	transform.NopResetter
+	bytes   map[rune]byte
+	replace byte
+}
+
+// Init initializes internal values of a character map.  This should
+// be done early, to minimize the cost of allocation of transforms
+// later.  It is not strictly necessary however, as the allocation
+// functions will arrange to call it if it has not already been done.
+func (c *Charmap) Init() {
+	c.once.Do(c.initialize)
+}
+
+func (c *Charmap) initialize() {
+	c.bytes = make(map[rune]byte)
+	ascii := true
+
+	for i := 0; i < 256; i++ {
+		r, ok := c.Map[byte(i)]
+		if !ok {
+			r = rune(i)
+		}
+		if r < 128 && r != rune(i) {
+			ascii = false
+		}
+		if r != RuneError {
+			c.bytes[r] = byte(i)
+		}
+		utf := make([]byte, utf8.RuneLen(r))
+		utf8.EncodeRune(utf, r)
+		c.runes[i] = utf
+	}
+	if ascii && c.ReplacementChar == '\x00' {
+		c.ReplacementChar = ASCIISub
+	}
+}
+
+// NewDecoder returns a Decoder the converts from the 8-bit
+// character set to UTF-8.  Unknown mappings, if any, are mapped
+// to '\uFFFD'.
+func (c *Charmap) NewDecoder() *encoding.Decoder {
+	c.Init()
+	return &encoding.Decoder{Transformer: &cmapDecoder{runes: c.runes}}
+}
+
+// NewEncoder returns a Transformer that converts from UTF8 to the
+// 8-bit character set.  Unknown mappings are mapped to 0x1A.
+func (c *Charmap) NewEncoder() *encoding.Encoder {
+	c.Init()
+	return &encoding.Encoder{
+		Transformer: &cmapEncoder{
+			bytes:   c.bytes,
+			replace: c.ReplacementChar,
+		},
+	}
+}
+
+func (d *cmapDecoder) Transform(dst, src []byte, atEOF bool) (int, int, error) {
+	var e error
+	var ndst, nsrc int
+
+	for _, c := range src {
+		b := d.runes[c]
+		l := len(b)
+
+		if ndst+l > len(dst) {
+			e = transform.ErrShortDst
+			break
+		}
+		for i := 0; i < l; i++ {
+			dst[ndst] = b[i]
+			ndst++
+		}
+		nsrc++
+	}
+	return ndst, nsrc, e
+}
+
+func (d *cmapEncoder) Transform(dst, src []byte, atEOF bool) (int, int, error) {
+	var e error
+	var ndst, nsrc int
+	for nsrc < len(src) {
+		if ndst >= len(dst) {
+			e = transform.ErrShortDst
+			break
+		}
+
+		r, sz := utf8.DecodeRune(src[nsrc:])
+		if r == utf8.RuneError && sz == 1 {
+			// If its inconclusive due to insufficient data in
+			// in the source, report it
+			if !atEOF && !utf8.FullRune(src[nsrc:]) {
+				e = transform.ErrShortSrc
+				break
+			}
+		}
+
+		if c, ok := d.bytes[r]; ok {
+			dst[ndst] = c
+		} else {
+			dst[ndst] = d.replace
+		}
+		nsrc += sz
+		ndst++
+	}
+
+	return ndst, nsrc, e
+}