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Side by Side Diff: pkg/compiler/lib/src/js_backend/constant_emitter.dart

Issue 938383005: Extends shortened representation of numbers to negative numbers. (Closed) Base URL: https://dart.googlecode.com/svn/branches/bleeding_edge/dart
Patch Set: Created 5 years, 9 months ago
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1 // Copyright (c) 2012, the Dart project authors. Please see the AUTHORS file 1 // Copyright (c) 2012, the Dart project authors. Please see the AUTHORS file
2 // for details. All rights reserved. Use of this source code is governed by a 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. 3 // BSD-style license that can be found in the LICENSE file.
4 4
5 part of js_backend; 5 part of js_backend;
6 6
7 class ConstantEmitter { 7 class ConstantEmitter {
8 ConstantReferenceEmitter _referenceEmitter; 8 ConstantReferenceEmitter _referenceEmitter;
9 ConstantLiteralEmitter _literalEmitter; 9 ConstantLiteralEmitter _literalEmitter;
10 10
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193 compiler.internalError(NO_LOCATION_SPANNABLE, 193 compiler.internalError(NO_LOCATION_SPANNABLE,
194 "The function constant does not need specific JS code."); 194 "The function constant does not need specific JS code.");
195 return null; 195 return null;
196 } 196 }
197 197
198 @override 198 @override
199 jsAst.Expression visitNull(NullConstantValue constant, [_]) { 199 jsAst.Expression visitNull(NullConstantValue constant, [_]) {
200 return new jsAst.LiteralNull(); 200 return new jsAst.LiteralNull();
201 } 201 }
202 202
203 static final _exponentialRE = new RegExp(
204 '^'
205 '\([-+]?\)' // 1: sign
206 '\([0-9]+\)' // 2: leading digit(s)
207 '\(\.\([0-9]*\)\)?' // 4: fraction digits
208 'e\([-+]?[0-9]+\)' // 5: exponent with sign
209 r'$');
210
203 /// Reduces the size of exponential representations when minification is 211 /// Reduces the size of exponential representations when minification is
204 /// enabled. 212 /// enabled.
205 /// 213 ///
206 /// Removes the "+" after the exponential sign, and removes the "." before the 214 /// Removes the "+" after the exponential sign, and removes the "." before the
207 /// "e". For example `1.23e+5` is changed to `123e3`. 215 /// "e". For example `1.23e+5` is changed to `123e3`.
208 String _shortenExponentialRepresentation(String numberString) { 216 String _shortenExponentialRepresentation(String numberString) {
209 if (numberString.length < 4) return numberString; 217 Match match = _exponentialRE.firstMatch(numberString);
210 if (numberString[1] == "e" && numberString[2] == "+") { 218 if (match == null) return numberString;
211 // For example: "1e+5". Remove the "+". 219 String sign = match[1];
212 return "${numberString[0]}e${numberString.substring(2)}"; 220 String leadingDigits = match[2];
213 } 221 String fractionDigits = match[4];
214 if (numberString[1] != ".") return numberString; 222 int exponent = int.parse(match[5]);
215 int digitsAfterDotCount = 0; 223 if (fractionDigits == null) fractionDigits = '';
216 int pos = 2; 224 exponent -= fractionDigits.length;
217 while (pos < numberString.length && numberString[pos] != "e") { 225 String result = '${sign}${leadingDigits}${fractionDigits}e${exponent}';
218 pos++;
219 digitsAfterDotCount++;
220 }
221 if (pos >= numberString.length) return numberString;
222 int exponent = int.parse(numberString.substring(pos + 1));
223 if (exponent <= digitsAfterDotCount) return numberString;
224 String digitsAfterDot = numberString.substring(2, pos);
225 int shiftedExponent = exponent - digitsAfterDotCount;
226 String result = "${numberString[0]}${digitsAfterDot}e$shiftedExponent";
227 assert(double.parse(result) == double.parse(numberString)); 226 assert(double.parse(result) == double.parse(numberString));
228 return result; 227 return result;
229 } 228 }
230 229
231 @override 230 @override
232 jsAst.Expression visitInt(IntConstantValue constant, [_]) { 231 jsAst.Expression visitInt(IntConstantValue constant, [_]) {
233 int primitiveValue = constant.primitiveValue; 232 int primitiveValue = constant.primitiveValue;
234 // Since we are in JavaScript we can shorten long integers to their 233 // Since we are in JavaScript we can shorten long integers to their shorter
235 // shorter exponential representation. 234 // exponential representation, for example: "1e4" is shorter than "10000".
236 // For example: "1e+4" is shorter than "10000".
237 // 235 //
238 // Note that this shortening apparently loses precision for big numbers 236 // Note that this shortening apparently loses precision for big numbers
239 // (like 1234567890123456789012345 which becomes 12345678901234568e8). 237 // (like 1234567890123456789012345 which becomes 12345678901234568e8).
240 // However, since JavaScript engines represent all numbers as doubles, 238 // However, since JavaScript engines represent all numbers as doubles, these
241 // these digits are lost anyway. 239 // digits are lost anyway.
242 int cutOffValue = compiler.enableMinification ? 10000 : 1e20.toInt(); 240 String representation = primitiveValue.toString();
243 if (primitiveValue.abs() >= cutOffValue) { 241 String alternative = null;
244 String exponential = _shortenExponentialRepresentation( 242
243 int cutoff = compiler.enableMinification ? 10000 : 1e10.toInt();
244 if (primitiveValue.abs() >= cutoff) {
245 alternative = _shortenExponentialRepresentation(
245 primitiveValue.toStringAsExponential()); 246 primitiveValue.toStringAsExponential());
246 String decimal = primitiveValue.toString();
247 return new jsAst.LiteralNumber(
248 (exponential.length < decimal.length) ? exponential : decimal);
249 } 247 }
250 return new jsAst.LiteralNumber('$primitiveValue'); 248 if (alternative != null && alternative.length < representation.length) {
249 representation = alternative;
250 }
251 return new jsAst.LiteralNumber(representation);
251 } 252 }
252 253
253 @override 254 @override
254 jsAst.Expression visitDouble(DoubleConstantValue constant, [_]) { 255 jsAst.Expression visitDouble(DoubleConstantValue constant, [_]) {
255 double value = constant.primitiveValue; 256 double value = constant.primitiveValue;
256 if (value.isNaN) { 257 if (value.isNaN) {
257 return js("0/0"); 258 return js("0/0");
258 } else if (value == double.INFINITY) { 259 } else if (value == double.INFINITY) {
259 return js("1/0"); 260 return js("1/0");
260 } else if (value == -double.INFINITY) { 261 } else if (value == -double.INFINITY) {
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444 [value, argumentList]); 445 [value, argumentList]);
445 } 446 }
446 return value; 447 return value;
447 } 448 }
448 449
449 @override 450 @override
450 jsAst.Expression visitDeferred(DeferredConstantValue constant, [_]) { 451 jsAst.Expression visitDeferred(DeferredConstantValue constant, [_]) {
451 return constantEmitter.reference(constant.referenced); 452 return constantEmitter.reference(constant.referenced);
452 } 453 }
453 } 454 }
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