github.com/go-xe2/third@v1.0.3/golang.org/x/text/internal/export/idna/trie.go (about)

     1  // Copyright 2016 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 idna
     6  
     7  // appendMapping appends the mapping for the respective rune. isMapped must be
     8  // true. A mapping is a categorization of a rune as defined in UTS #46.
     9  func (c info) appendMapping(b []byte, s string) []byte {
    10  	index := int(c >> indexShift)
    11  	if c&xorBit == 0 {
    12  		s := mappings[index:]
    13  		return append(b, s[1:s[0]+1]...)
    14  	}
    15  	b = append(b, s...)
    16  	if c&inlineXOR == inlineXOR {
    17  		// TODO: support and handle two-byte inline masks
    18  		b[len(b)-1] ^= byte(index)
    19  	} else {
    20  		for p := len(b) - int(xorData[index]); p < len(b); p++ {
    21  			index++
    22  			b[p] ^= xorData[index]
    23  		}
    24  	}
    25  	return b
    26  }
    27  
    28  // Sparse block handling code.
    29  
    30  type valueRange struct {
    31  	value  uint16 // header: value:stride
    32  	lo, hi byte   // header: lo:n
    33  }
    34  
    35  type sparseBlocks struct {
    36  	values []valueRange
    37  	offset []uint16
    38  }
    39  
    40  var idnaSparse = sparseBlocks{
    41  	values: idnaSparseValues[:],
    42  	offset: idnaSparseOffset[:],
    43  }
    44  
    45  // Don't use newIdnaTrie to avoid unconditional linking in of the table.
    46  var trie = &idnaTrie{}
    47  
    48  // lookup determines the type of block n and looks up the value for b.
    49  // For n < t.cutoff, the block is a simple lookup table. Otherwise, the block
    50  // is a list of ranges with an accompanying value. Given a matching range r,
    51  // the value for b is by r.value + (b - r.lo) * stride.
    52  func (t *sparseBlocks) lookup(n uint32, b byte) uint16 {
    53  	offset := t.offset[n]
    54  	header := t.values[offset]
    55  	lo := offset + 1
    56  	hi := lo + uint16(header.lo)
    57  	for lo < hi {
    58  		m := lo + (hi-lo)/2
    59  		r := t.values[m]
    60  		if r.lo <= b && b <= r.hi {
    61  			return r.value + uint16(b-r.lo)*header.value
    62  		}
    63  		if b < r.lo {
    64  			hi = m
    65  		} else {
    66  			lo = m + 1
    67  		}
    68  	}
    69  	return 0
    70  }