| // Copyright 2016 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 idna |
| |
| // Sparse block handling code. |
| |
| type valueRange struct { |
| value uint16 // header: value:stride |
| lo, hi byte // header: lo:n |
| } |
| |
| type sparseBlocks struct { |
| values []valueRange |
| offset []uint16 |
| } |
| |
| var idnaSparse = sparseBlocks{ |
| values: idnaSparseValues[:], |
| offset: idnaSparseOffset[:], |
| } |
| |
| // Don't use newIdnaTrie to avoid unconditional linking in of the table. |
| var trie = &idnaTrie{} |
| |
| // lookup determines the type of block n and looks up the value for b. |
| // For n < t.cutoff, the block is a simple lookup table. Otherwise, the block |
| // is a list of ranges with an accompanying value. Given a matching range r, |
| // the value for b is by r.value + (b - r.lo) * stride. |
| func (t *sparseBlocks) lookup(n uint32, b byte) uint16 { |
| offset := t.offset[n] |
| header := t.values[offset] |
| lo := offset + 1 |
| hi := lo + uint16(header.lo) |
| for lo < hi { |
| m := lo + (hi-lo)/2 |
| r := t.values[m] |
| if r.lo <= b && b <= r.hi { |
| return r.value + uint16(b-r.lo)*header.value |
| } |
| if b < r.lo { |
| hi = m |
| } else { |
| lo = m + 1 |
| } |
| } |
| return 0 |
| } |