// Copyright 2014 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 cases
import "golang.org/x/text/transform"
// A context is used for iterating over source bytes, fetching case info and
// writing to a destination buffer.
//
// Casing operations may need more than one rune of context to decide how a rune
// should be cased. Casing implementations should call checkpoint on context
// whenever it is known to be safe to return the runes processed so far.
//
// It is recommended for implementations to not allow for more than 30 case
// ignorables as lookahead (analogous to the limit in norm) and to use state if
// unbounded lookahead is needed for cased runes.
type context struct {
dst, src []byte
atEOF bool
pDst int // pDst points past the last written rune in dst.
pSrc int // pSrc points to the start of the currently scanned rune.
// checkpoints safe to return in Transform, where nDst <= pDst and nSrc <= pSrc.
nDst, nSrc int
err error
sz int // size of current rune
info info // case information of currently scanned rune
// State preserved across calls to Transform.
isMidWord bool // false if next cased letter needs to be title-cased.
}
func (c *context) Reset() {
c.isMidWord = false
}
// ret returns the return values for the Transform method. It checks whether
// there were insufficient bytes in src to complete and introduces an error
// accordingly, if necessary.
func (c *context) ret() (nDst, nSrc int, err error) {
if c.err != nil || c.nSrc == len(c.src) {
return c.nDst, c.nSrc, c.err
}
// This point is only reached by mappers if there was no short destination
// buffer. This means that the source buffer was exhausted and that c.sz was
// set to 0 by next.
if c.atEOF && c.pSrc == len(c.src) {
return c.pDst, c.pSrc, nil
}
return c.nDst, c.nSrc, transform.ErrShortSrc
}
// retSpan returns the return values for the Span method. It checks whether
// there were insufficient bytes in src to complete and introduces an error
// accordingly, if necessary.
func (c *context) retSpan() (n int, err error) {
_, nSrc, err := c.ret()
return nSrc, err
}
// checkpoint sets the return value buffer points for Transform to the current
// positions.
func (c *context) checkpoint() {
if c.err == nil {
c.nDst, c.nSrc = c.pDst, c.pSrc+c.sz
}
}
// unreadRune causes the last rune read by next to be reread on the next
// invocation of next. Only one unreadRune may be called after a call to next.
func (c *context) unreadRune() {
c.sz = 0
}
func (c *context) next() bool {
c.pSrc += c.sz
if c.pSrc == len(c.src) || c.err != nil {
c.info, c.sz = 0, 0
return false
}
v, sz := trie.lookup(c.src[c.pSrc:])
c.info, c.sz = info(v), sz
if c.sz == 0 {
if c.atEOF {
// A zero size means we have an incomplete rune. If we are atEOF,
// this means it is an illegal rune, which we will consume one
// byte at a time.
c.sz = 1
} else {
c.err = transform.ErrShortSrc
return false
}
}
return true
}
// writeBytes adds bytes to dst.
func (c *context) writeBytes(b []byte) bool {
if len(c.dst)-c.pDst < len(b) {
c.err = transform.ErrShortDst
return false
}
// This loop is faster than using copy.
for _, ch := range b {
c.dst[c.pDst] = ch
c.pDst++
}
return true
}
// writeString writes the given string to dst.
func (c *context) writeString(s string) bool {
if len(c.dst)-c.pDst < len(s) {
c.err = transform.ErrShortDst
return false
}
// This loop is faster than using copy.
for i := 0; i < len(s); i++ {
c.dst[c.pDst] = s[i]
c.pDst++
}
return true
}
// copy writes the current rune to dst.
func (c *context) copy() bool {
return c.writeBytes(c.src[c.pSrc : c.pSrc+c.sz])
}
// copyXOR copies the current rune to dst and modifies it by applying the XOR
// pattern of the case info. It is the responsibility of the caller to ensure
// that this is a rune with a XOR pattern defined.
func (c *context) copyXOR() bool {
if !c.copy() {
return false
}
if c.info&xorIndexBit == 0 {
// Fast path for 6-bit XOR pattern, which covers most cases.
c.dst[c.pDst-1] ^= byte(c.info >> xorShift)
} else {
// Interpret XOR bits as an index.
// TODO: test performance for unrolling this loop. Verify that we have
// at least two bytes and at most three.
idx := c.info >> xorShift
for p := c.pDst - 1; ; p-- {
c.dst[p] ^= xorData[idx]
idx--
if xorData[idx] == 0 {
break
}
}
}
return true
}
// hasPrefix returns true if src[pSrc:] starts with the given string.
func (c *context) hasPrefix(s string) bool {
b := c.src[c.pSrc:]
if len(b) < len(s) {
return false
}
for i, c := range b[:len(s)] {
if c != s[i] {
return false
}
}
return true
}
// caseType returns an info with only the case bits, normalized to either
// cLower, cUpper, cTitle or cUncased.
func (c *context) caseType() info {
cm := c.info & 0x7
if cm < 4 {
return cm
}
if cm >= cXORCase {
// xor the last bit of the rune with the case type bits.
b := c.src[c.pSrc+c.sz-1]
return info(b&1) ^ cm&0x3
}
if cm == cIgnorableCased {
return cLower
}
return cUncased
}
// lower writes the lowercase version of the current rune to dst.
func lower(c *context) bool {
ct := c.caseType()
if c.info&hasMappingMask == 0 || ct == cLower {
return c.copy()
}
if c.info&exceptionBit == 0 {
return c.copyXOR()
}
e := exceptions[c.info>>exceptionShift:]
offset := 2 + e[0]&lengthMask // size of header + fold string
if nLower := (e[1] >> lengthBits) & lengthMask; nLower != noChange {
return c.writeString(e[offset : offset+nLower])
}
return c.copy()
}
func isLower(c *context) bool {
ct := c.caseType()
if c.info&hasMappingMask == 0 || ct == cLower {
return true
}
if c.info&exceptionBit == 0 {
c.err = transform.ErrEndOfSpan
return false
}
e := exceptions[c.info>>exceptionShift:]
if nLower := (e[1] >> lengthBits) & lengthMask; nLower != noChange {
c.err = transform.ErrEndOfSpan
return false
}
return true
}
// upper writes the uppercase version of the current rune to dst.
func upper(c *context) bool {
ct := c.caseType()
if c.info&hasMappingMask == 0 || ct == cUpper {
return c.copy()
}
if c.info&exceptionBit == 0 {
return c.copyXOR()
}
e := exceptions[c.info>>exceptionShift:]
offset := 2 + e[0]&lengthMask // size of header + fold string
// Get length of first special case mapping.
n := (e[1] >> lengthBits) & lengthMask
if ct == cTitle {
// The first special case mapping is for lower. Set n to the second.
if n == noChange {
n = 0
}
n, e = e[1]&lengthMask, e[n:]
}
if n != noChange {
return c.writeString(e[offset : offset+n])
}
return c.copy()
}
// isUpper writes the isUppercase version of the current rune to dst.
func isUpper(c *context) bool {
ct := c.caseType()
if c.info&hasMappingMask == 0 || ct == cUpper {
return true
}
if c.info&exceptionBit == 0 {
c.err = transform.ErrEndOfSpan
return false
}
e := exceptions[c.info>>exceptionShift:]
// Get length of first special case mapping.
n := (e[1] >> lengthBits) & lengthMask
if ct == cTitle {
n = e[1] & lengthMask
}
if n != noChange {
c.err = transform.ErrEndOfSpan
return false
}
return true
}
// title writes the title case version of the current rune to dst.
func title(c *context) bool {
ct := c.caseType()
if c.info&hasMappingMask == 0 || ct == cTitle {
return c.copy()
}
if c.info&exceptionBit == 0 {
if ct == cLower {
return c.copyXOR()
}
return c.copy()
}
// Get the exception data.
e := exceptions[c.info>>exceptionShift:]
offset := 2 + e[0]&lengthMask // size of header + fold string
nFirst := (e[1] >> lengthBits) & lengthMask
if nTitle := e[1] & lengthMask; nTitle != noChange {
if nFirst != noChange {
e = e[nFirst:]
}
return c.writeString(e[offset : offset+nTitle])
}
if ct == cLower && nFirst != noChange {
// Use the uppercase version instead.
return c.writeString(e[offset : offset+nFirst])
}
// Already in correct case.
return c.copy()
}
// isTitle reports whether the current rune is in title case.
func isTitle(c *context) bool {
ct := c.caseType()
if c.info&hasMappingMask == 0 || ct == cTitle {
return true
}
if c.info&exceptionBit == 0 {
if ct == cLower {
c.err = transform.ErrEndOfSpan
return false
}
return true
}
// Get the exception data.
e := exceptions[c.info>>exceptionShift:]
if nTitle := e[1] & lengthMask; nTitle != noChange {
c.err = transform.ErrEndOfSpan
return false
}
nFirst := (e[1] >> lengthBits) & lengthMask
if ct == cLower && nFirst != noChange {
c.err = transform.ErrEndOfSpan
return false
}
return true
}
// foldFull writes the foldFull version of the current rune to dst.
func foldFull(c *context) bool {
if c.info&hasMappingMask == 0 {
return c.copy()
}
ct := c.caseType()
if c.info&exceptionBit == 0 {
if ct != cLower || c.info&inverseFoldBit != 0 {
return c.copyXOR()
}
return c.copy()
}
e := exceptions[c.info>>exceptionShift:]
n := e[0] & lengthMask
if n == 0 {
if ct == cLower {
return c.copy()
}
n = (e[1] >> lengthBits) & lengthMask
}
return c.writeString(e[2 : 2+n])
}
// isFoldFull reports whether the current run is mapped to foldFull
func isFoldFull(c *context) bool {
if c.info&hasMappingMask == 0 {
return true
}
ct := c.caseType()
if c.info&exceptionBit == 0 {
if ct != cLower || c.info&inverseFoldBit != 0 {
c.err = transform.ErrEndOfSpan
return false
}
return true
}
e := exceptions[c.info>>exceptionShift:]
n := e[0] & lengthMask
if n == 0 && ct == cLower {
return true
}
c.err = transform.ErrEndOfSpan
return false
}
