path: root/Godeps/_workspace/src/golang.org/x/text/encoding/charmap/charmap.go

// 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.

//go:generate go run maketables.go

// Package charmap provides simple character encodings such as IBM Code Page 437
// and Windows 1252.
package charmap

import (
    "unicode/utf8"

    "golang.org/x/text/encoding"
    "golang.org/x/text/encoding/internal"
    "golang.org/x/text/encoding/internal/identifier"
    "golang.org/x/text/transform"
)

// These encodings vary only in the way clients should interpret them. Their
// coded character set is identical and a single implementation can be shared.
var (
    // ISO8859_6E is the ISO 8859-6E encoding.
    ISO8859_6E encoding.Encoding = &iso8859_6E

    // ISO8859_6I is the ISO 8859-6I encoding.
    ISO8859_6I encoding.Encoding = &iso8859_6I

    // ISO8859_8E is the ISO 8859-8E encoding.
    ISO8859_8E encoding.Encoding = &iso8859_8E

    // ISO8859_8I is the ISO 8859-8I encoding.
    ISO8859_8I encoding.Encoding = &iso8859_8I

    iso8859_6E = internal.Encoding{
        ISO8859_6,
        "ISO-8859-6E",
        identifier.ISO88596E,
    }

    iso8859_6I = internal.Encoding{
        ISO8859_6,
        "ISO-8859-6I",
        identifier.ISO88596I,
    }

    iso8859_8E = internal.Encoding{
        ISO8859_8,
        "ISO-8859-8E",
        identifier.ISO88598E,
    }

    iso8859_8I = internal.Encoding{
        ISO8859_8,
        "ISO-8859-8I",
        identifier.ISO88598I,
    }
)

// All is a list of all defined encodings in this package.
var All = listAll

// TODO: implement these encodings, in order of importance.
// ASCII, ISO8859_1:       Rather common. Close to Windows 1252.
// ISO8859_9:              Close to Windows 1254.

// utf8Enc holds a rune's UTF-8 encoding in data[:len].
type utf8Enc struct {
    len  uint8
    data [3]byte
}

// charmap describes an 8-bit character set encoding.
type charmap struct {
    // name is the encoding's name.
    name string
    // mib is the encoding type of this encoder.
    mib identifier.MIB
    // asciiSuperset states whether the encoding is a superset of ASCII.
    asciiSuperset bool
    // low is the lower bound of the encoded byte for a non-ASCII rune. If
    // charmap.asciiSuperset is true then this will be 0x80, otherwise 0x00.
    low uint8
    // replacement is the encoded replacement character.
    replacement byte
    // decode is the map from encoded byte to UTF-8.
    decode [256]utf8Enc
    // encoding is the map from runes to encoded bytes. Each entry is a
    // uint32: the high 8 bits are the encoded byte and the low 24 bits are
    // the rune. The table entries are sorted by ascending rune.
    encode [256]uint32
}

func (m *charmap) NewDecoder() *encoding.Decoder {
    return &encoding.Decoder{Transformer: charmapDecoder{charmap: m}}
}

func (m *charmap) NewEncoder() *encoding.Encoder {
    return &encoding.Encoder{Transformer: charmapEncoder{charmap: m}}
}

func (m *charmap) String() string {
    return m.name
}

func (m *charmap) ID() (mib identifier.MIB, other string) {
    return m.mib, ""
}

// charmapDecoder implements transform.Transformer by decoding to UTF-8.
type charmapDecoder struct {
    transform.NopResetter
    charmap *charmap
}

func (m charmapDecoder) Transform(dst, src []byte, atEOF bool) (nDst, nSrc int, err error) {
    for i, c := range src {
        if m.charmap.asciiSuperset && c < utf8.RuneSelf {
            if nDst >= len(dst) {
                err = transform.ErrShortDst
                break
            }
            dst[nDst] = c
            nDst++
            nSrc = i + 1
            continue
        }

        decode := &m.charmap.decode[c]
        n := int(decode.len)
        if nDst+n > len(dst) {
            err = transform.ErrShortDst
            break
        }
        // It's 15% faster to avoid calling copy for these tiny slices.
        for j := 0; j < n; j++ {
            dst[nDst] = decode.data[j]
            nDst++
        }
        nSrc = i + 1
    }
    return nDst, nSrc, err
}

// charmapEncoder implements transform.Transformer by encoding from UTF-8.
type charmapEncoder struct {
    transform.NopResetter
    charmap *charmap
}

func (m charmapEncoder) Transform(dst, src []byte, atEOF bool) (nDst, nSrc int, err error) {
    r, size := rune(0), 0
loop:
    for nSrc < len(src) {
        if nDst >= len(dst) {
            err = transform.ErrShortDst
            break
        }
        r = rune(src[nSrc])

        // Decode a 1-byte rune.
        if r < utf8.RuneSelf {
            if m.charmap.asciiSuperset {
                nSrc++
                dst[nDst] = uint8(r)
                nDst++
                continue
            }
            size = 1

        } else {
            // Decode a multi-byte rune.
            r, size = utf8.DecodeRune(src[nSrc:])
            if size == 1 {
                // All valid runes of size 1 (those below utf8.RuneSelf) were
                // handled above. We have invalid UTF-8 or we haven't seen the
                // full character yet.
                if !atEOF && !utf8.FullRune(src[nSrc:]) {
                    err = transform.ErrShortSrc
                } else {
                    err = internal.RepertoireError(m.charmap.replacement)
                }
                break
            }
        }

        // Binary search in [low, high) for that rune in the m.charmap.encode table.
        for low, high := int(m.charmap.low), 0x100; ; {
            if low >= high {
                err = internal.RepertoireError(m.charmap.replacement)
                break loop
            }
            mid := (low + high) / 2
            got := m.charmap.encode[mid]
            gotRune := rune(got & (1<<24 - 1))
            if gotRune < r {
                low = mid + 1
            } else if gotRune > r {
                high = mid
            } else {
                dst[nDst] = byte(got >> 24)
                nDst++
                break
            }
        }
        nSrc += size
    }
    return nDst, nSrc, err
}