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1 // Copyright (c) 2011, the Dart project authors. Please see the AUTHORS file | |
2 // for details. All rights reserved. Use of this source code is governed by a | |
3 // BSD-style license that can be found in the LICENSE file. | |
4 | |
5 /** | |
6 * Assigns JavaScript identifiers to Dart variables, class-names and members. | |
7 */ | |
8 class MinifyNamer extends Namer { | |
9 MinifyNamer(Compiler compiler) : super(compiler); | |
10 | |
11 String get ISOLATE => 'I'; | |
12 String get ISOLATE_PROPERTIES => 'p'; | |
13 bool get shouldMinify => true; | |
14 | |
15 const ALPHABET_CHARACTERS = 52; // a-zA-Z. | |
16 const ALPHANUMERIC_CHARACTERS = 62; // a-zA-Z0-9. | |
17 | |
18 String getFreshName(String proposedName, Set<String> usedNames) { | |
floitsch
2012/11/13 13:35:02
Add comment that the proposedName does not need to
erikcorry
2012/11/16 10:08:30
Done.
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19 var freshName; | |
20 if (proposedName.startsWith(r'call$')) { | |
floitsch
2012/11/13 13:35:02
This won't work if we mangle constantNames. If the
erikcorry
2012/11/16 10:08:30
Good catch. I moved the special handling of the c
| |
21 // We don't mangle the closure invoking function name because it is | |
22 // generated in applyFunction. | |
23 freshName = proposedName; | |
24 } else { | |
25 freshName = _getUnusedName(proposedName, usedNames); | |
26 } | |
27 usedNames.add(freshName); | |
28 return freshName; | |
29 } | |
30 | |
31 // This gets a minified name based on a hash of the proposed name. This | |
32 // is slightly less efficient than just getting the next name in a series, | |
33 // but it means that small changes in the input program will give smallish | |
34 // changes in the output, which can be useful for diffing etc. | |
35 String _getUnusedName(String proposedName, Set<String> usedNames) { | |
36 // Try single-character names with characters that occur in the | |
37 // input. | |
38 for (int i = 0; i < proposedName.length; i++) { | |
39 String candidate = proposedName[i]; | |
40 int code = candidate.charCodeAt(0); | |
41 if (code < $A) continue; | |
42 if (code > $z) continue; | |
43 if (code > $Z && code < $a) continue; | |
44 if (!usedNames.contains(candidate)) return candidate; | |
45 } | |
46 | |
47 int hash = _calculateHash(proposedName); | |
48 // Avoid very small hashes that won't try many names. | |
49 hash = hash < 1000 ? hash * 314159 : hash; // Yes, it's prime. | |
50 | |
51 // Try other n-character names based on the hash. We try one to three | |
52 // character identifiers. For each length we try around 10 different names | |
53 // in a predictable order determined by the proposed name. This is in order | |
54 // to make the renamer stable: small changes in the input should nornally | |
55 // result in relatively small changes in the output. | |
56 for (var n = 1; n <= 3; n++) { | |
57 int h = hash; | |
58 while (h > 10) { | |
59 var codes = <int>[_letterNumber(h)]; | |
60 int h2 = h ~/ ALPHABET_CHARACTERS; | |
61 for (var i = 1; i < n; i++) { | |
62 codes.add(_alphaNumericNumber(h2)); | |
63 h2 ~/= ALPHANUMERIC_CHARACTERS; | |
64 } | |
65 final candidate = new String.fromCharCodes(codes); | |
66 if (!usedNames.contains(candidate) && !jsReserved.contains(candidate)) { | |
67 return candidate; | |
68 } | |
69 // Try again with a slightly different hash. After around 10 turns | |
70 // around this loop h is zero and we try a longer name. | |
71 h ~/= 7; | |
72 } | |
73 } | |
74 | |
75 // If we can't find a hash based name in the three-letter space, then base | |
76 // the name on a letter and a counter. | |
77 proposedName = new String.fromCharCodes([_letterNumber(hash)]); | |
78 var i = 0; | |
79 while (usedNames.contains("$proposedName$i")) { | |
80 i++; | |
81 } | |
82 return "$proposedName$i"; | |
83 } | |
84 | |
85 int _calculateHash(String name) { | |
86 int h = 0; | |
87 for (int i = 0; i < name.length; i++) { | |
88 h += name.charCodeAt(i); | |
89 h &= 0xffffffff; | |
90 h += h << 10; | |
91 h &= 0xffffffff; | |
92 h ^= h >> 6; | |
93 h &= 0xffffffff; | |
94 } | |
95 return h; | |
96 } | |
97 | |
98 int _letterNumber(int x) { | |
99 if (x >= ALPHABET_CHARACTERS) x %= ALPHABET_CHARACTERS; | |
100 if (x < 26) return $a + x; | |
101 return $A + x - 26; | |
102 } | |
103 | |
104 int _alphaNumericNumber(int x) { | |
105 if (x >= ALPHANUMERIC_CHARACTERS) x %= ALPHANUMERIC_CHARACTERS; | |
106 if (x < 26) return $a + x; | |
107 if (x < 52) return $A + x - 26; | |
108 return $0 + x - 52; | |
109 } | |
110 | |
111 } | |
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