golang.org/x/text@v0.14.0/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  // Sparse block handling code.
     8  
     9  type valueRange struct {
    10  	value  uint16 // header: value:stride
    11  	lo, hi byte   // header: lo:n
    12  }
    13  
    14  type sparseBlocks struct {
    15  	values []valueRange
    16  	offset []uint16
    17  }
    18  
    19  var idnaSparse = sparseBlocks{
    20  	values: idnaSparseValues[:],
    21  	offset: idnaSparseOffset[:],
    22  }
    23  
    24  // Don't use newIdnaTrie to avoid unconditional linking in of the table.
    25  var trie = &idnaTrie{}
    26  
    27  // lookup determines the type of block n and looks up the value for b.
    28  // For n < t.cutoff, the block is a simple lookup table. Otherwise, the block
    29  // is a list of ranges with an accompanying value. Given a matching range r,
    30  // the value for b is by r.value + (b - r.lo) * stride.
    31  func (t *sparseBlocks) lookup(n uint32, b byte) uint16 {
    32  	offset := t.offset[n]
    33  	header := t.values[offset]
    34  	lo := offset + 1
    35  	hi := lo + uint16(header.lo)
    36  	for lo < hi {
    37  		m := lo + (hi-lo)/2
    38  		r := t.values[m]
    39  		if r.lo <= b && b <= r.hi {
    40  			return r.value + uint16(b-r.lo)*header.value
    41  		}
    42  		if b < r.lo {
    43  			hi = m
    44  		} else {
    45  			lo = m + 1
    46  		}
    47  	}
    48  	return 0
    49  }