khenaidoo | ac63710 | 2019-01-14 15:44:34 -0500 | [diff] [blame] | 1 | // Copyright 2015 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 colltab |
| 6 | |
| 7 | // An Iter incrementally converts chunks of the input text to collation |
| 8 | // elements, while ensuring that the collation elements are in normalized order |
| 9 | // (that is, they are in the order as if the input text were normalized first). |
| 10 | type Iter struct { |
| 11 | Weighter Weighter |
| 12 | Elems []Elem |
| 13 | // N is the number of elements in Elems that will not be reordered on |
| 14 | // subsequent iterations, N <= len(Elems). |
| 15 | N int |
| 16 | |
| 17 | bytes []byte |
| 18 | str string |
| 19 | // Because the Elems buffer may contain collation elements that are needed |
| 20 | // for look-ahead, we need two positions in the text (bytes or str): one for |
| 21 | // the end position in the text for the current iteration and one for the |
| 22 | // start of the next call to appendNext. |
| 23 | pEnd int // end position in text corresponding to N. |
| 24 | pNext int // pEnd <= pNext. |
| 25 | } |
| 26 | |
| 27 | // Reset sets the position in the current input text to p and discards any |
| 28 | // results obtained so far. |
| 29 | func (i *Iter) Reset(p int) { |
| 30 | i.Elems = i.Elems[:0] |
| 31 | i.N = 0 |
| 32 | i.pEnd = p |
| 33 | i.pNext = p |
| 34 | } |
| 35 | |
| 36 | // Len returns the length of the input text. |
| 37 | func (i *Iter) Len() int { |
| 38 | if i.bytes != nil { |
| 39 | return len(i.bytes) |
| 40 | } |
| 41 | return len(i.str) |
| 42 | } |
| 43 | |
| 44 | // Discard removes the collation elements up to N. |
| 45 | func (i *Iter) Discard() { |
| 46 | // TODO: change this such that only modifiers following starters will have |
| 47 | // to be copied. |
| 48 | i.Elems = i.Elems[:copy(i.Elems, i.Elems[i.N:])] |
| 49 | i.N = 0 |
| 50 | } |
| 51 | |
| 52 | // End returns the end position of the input text for which Next has returned |
| 53 | // results. |
| 54 | func (i *Iter) End() int { |
| 55 | return i.pEnd |
| 56 | } |
| 57 | |
| 58 | // SetInput resets i to input s. |
| 59 | func (i *Iter) SetInput(s []byte) { |
| 60 | i.bytes = s |
| 61 | i.str = "" |
| 62 | i.Reset(0) |
| 63 | } |
| 64 | |
| 65 | // SetInputString resets i to input s. |
| 66 | func (i *Iter) SetInputString(s string) { |
| 67 | i.str = s |
| 68 | i.bytes = nil |
| 69 | i.Reset(0) |
| 70 | } |
| 71 | |
| 72 | func (i *Iter) done() bool { |
| 73 | return i.pNext >= len(i.str) && i.pNext >= len(i.bytes) |
| 74 | } |
| 75 | |
| 76 | func (i *Iter) appendNext() bool { |
| 77 | if i.done() { |
| 78 | return false |
| 79 | } |
| 80 | var sz int |
| 81 | if i.bytes == nil { |
| 82 | i.Elems, sz = i.Weighter.AppendNextString(i.Elems, i.str[i.pNext:]) |
| 83 | } else { |
| 84 | i.Elems, sz = i.Weighter.AppendNext(i.Elems, i.bytes[i.pNext:]) |
| 85 | } |
| 86 | if sz == 0 { |
| 87 | sz = 1 |
| 88 | } |
| 89 | i.pNext += sz |
| 90 | return true |
| 91 | } |
| 92 | |
| 93 | // Next appends Elems to the internal array. On each iteration, it will either |
| 94 | // add starters or modifiers. In the majority of cases, an Elem with a primary |
| 95 | // value > 0 will have a CCC of 0. The CCC values of collation elements are also |
| 96 | // used to detect if the input string was not normalized and to adjust the |
| 97 | // result accordingly. |
| 98 | func (i *Iter) Next() bool { |
| 99 | if i.N == len(i.Elems) && !i.appendNext() { |
| 100 | return false |
| 101 | } |
| 102 | |
| 103 | // Check if the current segment starts with a starter. |
| 104 | prevCCC := i.Elems[len(i.Elems)-1].CCC() |
| 105 | if prevCCC == 0 { |
| 106 | i.N = len(i.Elems) |
| 107 | i.pEnd = i.pNext |
| 108 | return true |
| 109 | } else if i.Elems[i.N].CCC() == 0 { |
| 110 | // set i.N to only cover part of i.Elems for which prevCCC == 0 and |
| 111 | // use rest for the next call to next. |
| 112 | for i.N++; i.N < len(i.Elems) && i.Elems[i.N].CCC() == 0; i.N++ { |
| 113 | } |
| 114 | i.pEnd = i.pNext |
| 115 | return true |
| 116 | } |
| 117 | |
| 118 | // The current (partial) segment starts with modifiers. We need to collect |
| 119 | // all successive modifiers to ensure that they are normalized. |
| 120 | for { |
| 121 | p := len(i.Elems) |
| 122 | i.pEnd = i.pNext |
| 123 | if !i.appendNext() { |
| 124 | break |
| 125 | } |
| 126 | |
| 127 | if ccc := i.Elems[p].CCC(); ccc == 0 || len(i.Elems)-i.N > maxCombiningCharacters { |
| 128 | // Leave the starter for the next iteration. This ensures that we |
| 129 | // do not return sequences of collation elements that cross two |
| 130 | // segments. |
| 131 | // |
| 132 | // TODO: handle large number of combining characters by fully |
| 133 | // normalizing the input segment before iteration. This ensures |
| 134 | // results are consistent across the text repo. |
| 135 | i.N = p |
| 136 | return true |
| 137 | } else if ccc < prevCCC { |
| 138 | i.doNorm(p, ccc) // should be rare, never occurs for NFD and FCC. |
| 139 | } else { |
| 140 | prevCCC = ccc |
| 141 | } |
| 142 | } |
| 143 | |
| 144 | done := len(i.Elems) != i.N |
| 145 | i.N = len(i.Elems) |
| 146 | return done |
| 147 | } |
| 148 | |
| 149 | // nextNoNorm is the same as next, but does not "normalize" the collation |
| 150 | // elements. |
| 151 | func (i *Iter) nextNoNorm() bool { |
| 152 | // TODO: remove this function. Using this instead of next does not seem |
| 153 | // to improve performance in any significant way. We retain this until |
| 154 | // later for evaluation purposes. |
| 155 | if i.done() { |
| 156 | return false |
| 157 | } |
| 158 | i.appendNext() |
| 159 | i.N = len(i.Elems) |
| 160 | return true |
| 161 | } |
| 162 | |
| 163 | const maxCombiningCharacters = 30 |
| 164 | |
| 165 | // doNorm reorders the collation elements in i.Elems. |
| 166 | // It assumes that blocks of collation elements added with appendNext |
| 167 | // either start and end with the same CCC or start with CCC == 0. |
| 168 | // This allows for a single insertion point for the entire block. |
| 169 | // The correctness of this assumption is verified in builder.go. |
| 170 | func (i *Iter) doNorm(p int, ccc uint8) { |
| 171 | n := len(i.Elems) |
| 172 | k := p |
| 173 | for p--; p > i.N && ccc < i.Elems[p-1].CCC(); p-- { |
| 174 | } |
| 175 | i.Elems = append(i.Elems, i.Elems[p:k]...) |
| 176 | copy(i.Elems[p:], i.Elems[k:]) |
| 177 | i.Elems = i.Elems[:n] |
| 178 | } |