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27
28#ifndef DOUBLE_CONVERSION_DOUBLE_TO_STRING_H_
29#define DOUBLE_CONVERSION_DOUBLE_TO_STRING_H_
30
31#include "utils.h"
32
33namespace double_conversion {
34
35class DoubleToStringConverter {
36 public:
37 // When calling ToFixed with a double > 10^kMaxFixedDigitsBeforePoint
38 // or a requested_digits parameter > kMaxFixedDigitsAfterPoint then the
39 // function returns false.
40 static const int kMaxFixedDigitsBeforePoint = 60;
41 static const int kMaxFixedDigitsAfterPoint = 100;
42
43 // When calling ToExponential with a requested_digits
44 // parameter > kMaxExponentialDigits then the function returns false.
45 static const int kMaxExponentialDigits = 120;
46
47 // When calling ToPrecision with a requested_digits
48 // parameter < kMinPrecisionDigits or requested_digits > kMaxPrecisionDigits
49 // then the function returns false.
50 static const int kMinPrecisionDigits = 1;
51 static const int kMaxPrecisionDigits = 120;
52
53 // The maximal number of digits that are needed to emit a double in base 10.
54 // A higher precision can be achieved by using more digits, but the shortest
55 // accurate representation of any double will never use more digits than
56 // kBase10MaximalLength.
57 // Note that DoubleToAscii null-terminates its input. So the given buffer
58 // should be at least kBase10MaximalLength + 1 characters long.
59 static const int kBase10MaximalLength = 17;
60
61 // The maximal number of digits that are needed to emit a single in base 10.
62 // A higher precision can be achieved by using more digits, but the shortest
63 // accurate representation of any single will never use more digits than
64 // kBase10MaximalLengthSingle.
65 static const int kBase10MaximalLengthSingle = 9;
66
67 // The length of the longest string that 'ToShortest' can produce when the
68 // converter is instantiated with EcmaScript defaults (see
69 // 'EcmaScriptConverter')
70 // This value does not include the trailing '\0' character.
71 // This amount of characters is needed for negative values that hit the
72 // 'decimal_in_shortest_low' limit. For example: "-0.0000033333333333333333"
73 static const int kMaxCharsEcmaScriptShortest = 25;
74
75 enum Flags {
76 NO_FLAGS = 0,
77 EMIT_POSITIVE_EXPONENT_SIGN = 1,
78 EMIT_TRAILING_DECIMAL_POINT = 2,
79 EMIT_TRAILING_ZERO_AFTER_POINT = 4,
80 UNIQUE_ZERO = 8,
81 NO_TRAILING_ZERO = 16
82 };
83
84 // Flags should be a bit-or combination of the possible Flags-enum.
85 // - NO_FLAGS: no special flags.
86 // - EMIT_POSITIVE_EXPONENT_SIGN: when the number is converted into exponent
87 // form, emits a '+' for positive exponents. Example: 1.2e+2.
88 // - EMIT_TRAILING_DECIMAL_POINT: when the input number is an integer and is
89 // converted into decimal format then a trailing decimal point is appended.
90 // Example: 2345.0 is converted to "2345.".
91 // - EMIT_TRAILING_ZERO_AFTER_POINT: in addition to a trailing decimal point
92 // emits a trailing '0'-character. This flag requires the
93 // EMIT_TRAILING_DECIMAL_POINT flag.
94 // Example: 2345.0 is converted to "2345.0".
95 // - UNIQUE_ZERO: "-0.0" is converted to "0.0".
96 // - NO_TRAILING_ZERO: Trailing zeros are removed from the fractional portion
97 // of the result in precision mode. Matches printf's %g.
98 // When EMIT_TRAILING_ZERO_AFTER_POINT is also given, one trailing zero is
99 // preserved.
100 //
101 // Infinity symbol and nan_symbol provide the string representation for these
102 // special values. If the string is NULL and the special value is encountered
103 // then the conversion functions return false.
104 //
105 // The exponent_character is used in exponential representations. It is
106 // usually 'e' or 'E'.
107 //
108 // When converting to the shortest representation the converter will
109 // represent input numbers in decimal format if they are in the interval
110 // [10^decimal_in_shortest_low; 10^decimal_in_shortest_high[
111 // (lower boundary included, greater boundary excluded).
112 // Example: with decimal_in_shortest_low = -6 and
113 // decimal_in_shortest_high = 21:
114 // ToShortest(0.000001) -> "0.000001"
115 // ToShortest(0.0000001) -> "1e-7"
116 // ToShortest(111111111111111111111.0) -> "111111111111111110000"
117 // ToShortest(100000000000000000000.0) -> "100000000000000000000"
118 // ToShortest(1111111111111111111111.0) -> "1.1111111111111111e+21"
119 //
120 // When converting to precision mode the converter may add
121 // max_leading_padding_zeroes before returning the number in exponential
122 // format.
123 // Example with max_leading_padding_zeroes_in_precision_mode = 6.
124 // ToPrecision(0.0000012345, 2) -> "0.0000012"
125 // ToPrecision(0.00000012345, 2) -> "1.2e-7"
126 // Similarly the converter may add up to
127 // max_trailing_padding_zeroes_in_precision_mode in precision mode to avoid
128 // returning an exponential representation. A zero added by the
129 // EMIT_TRAILING_ZERO_AFTER_POINT flag is counted for this limit.
130 // Examples for max_trailing_padding_zeroes_in_precision_mode = 1:
131 // ToPrecision(230.0, 2) -> "230"
132 // ToPrecision(230.0, 2) -> "230." with EMIT_TRAILING_DECIMAL_POINT.
133 // ToPrecision(230.0, 2) -> "2.3e2" with EMIT_TRAILING_ZERO_AFTER_POINT.
134 //
135 // The min_exponent_width is used for exponential representations.
136 // The converter adds leading '0's to the exponent until the exponent
137 // is at least min_exponent_width digits long.
138 // The min_exponent_width is clamped to 5.
139 // As such, the exponent may never have more than 5 digits in total.
140 DoubleToStringConverter(int flags,
141 const char* infinity_symbol,
142 const char* nan_symbol,
143 char exponent_character,
144 int decimal_in_shortest_low,
145 int decimal_in_shortest_high,
146 int max_leading_padding_zeroes_in_precision_mode,
147 int max_trailing_padding_zeroes_in_precision_mode,
148 int min_exponent_width = 0)
149 : flags_(flags),
150 infinity_symbol_(infinity_symbol),
151 nan_symbol_(nan_symbol),
152 exponent_character_(exponent_character),
153 decimal_in_shortest_low_(decimal_in_shortest_low),
154 decimal_in_shortest_high_(decimal_in_shortest_high),
155 max_leading_padding_zeroes_in_precision_mode_(
156 max_leading_padding_zeroes_in_precision_mode),
157 max_trailing_padding_zeroes_in_precision_mode_(
158 max_trailing_padding_zeroes_in_precision_mode),
159 min_exponent_width_(min_exponent_width) {
160 // When 'trailing zero after the point' is set, then 'trailing point'
161 // must be set too.
162 DOUBLE_CONVERSION_ASSERT(((flags & EMIT_TRAILING_DECIMAL_POINT) != 0) ||
163 !((flags & EMIT_TRAILING_ZERO_AFTER_POINT) != 0));
164 }
165
166 // Returns a converter following the EcmaScript specification.
167 //
168 // Flags: UNIQUE_ZERO and EMIT_POSITIVE_EXPONENT_SIGN.
169 // Special values: "Infinity" and "NaN".
170 // Lower case 'e' for exponential values.
171 // decimal_in_shortest_low: -6
172 // decimal_in_shortest_high: 21
173 // max_leading_padding_zeroes_in_precision_mode: 6
174 // max_trailing_padding_zeroes_in_precision_mode: 0
175 static const DoubleToStringConverter& EcmaScriptConverter();
176
177 // Computes the shortest string of digits that correctly represent the input
178 // number. Depending on decimal_in_shortest_low and decimal_in_shortest_high
179 // (see constructor) it then either returns a decimal representation, or an
180 // exponential representation.
181 // Example with decimal_in_shortest_low = -6,
182 // decimal_in_shortest_high = 21,
183 // EMIT_POSITIVE_EXPONENT_SIGN activated, and
184 // EMIT_TRAILING_DECIMAL_POINT deactivated:
185 // ToShortest(0.000001) -> "0.000001"
186 // ToShortest(0.0000001) -> "1e-7"
187 // ToShortest(111111111111111111111.0) -> "111111111111111110000"
188 // ToShortest(100000000000000000000.0) -> "100000000000000000000"
189 // ToShortest(1111111111111111111111.0) -> "1.1111111111111111e+21"
190 //
191 // Note: the conversion may round the output if the returned string
192 // is accurate enough to uniquely identify the input-number.
193 // For example the most precise representation of the double 9e59 equals
194 // "899999999999999918767229449717619953810131273674690656206848", but
195 // the converter will return the shorter (but still correct) "9e59".
196 //
197 // Returns true if the conversion succeeds. The conversion always succeeds
198 // except when the input value is special and no infinity_symbol or
199 // nan_symbol has been given to the constructor.
200 //
201 // The length of the longest result is the maximum of the length of the
202 // following string representations (each with possible examples):
203 // - NaN and negative infinity: "NaN", "-Infinity", "-inf".
204 // - -10^(decimal_in_shortest_high - 1):
205 // "-100000000000000000000", "-1000000000000000.0"
206 // - the longest string in range [0; -10^decimal_in_shortest_low]. Generally,
207 // this string is 3 + kBase10MaximalLength - decimal_in_shortest_low.
208 // (Sign, '0', decimal point, padding zeroes for decimal_in_shortest_low,
209 // and the significant digits).
210 // "-0.0000033333333333333333", "-0.0012345678901234567"
211 // - the longest exponential representation. (A negative number with
212 // kBase10MaximalLength significant digits).
213 // "-1.7976931348623157e+308", "-1.7976931348623157E308"
214 // In addition, the buffer must be able to hold the trailing '\0' character.
215 bool ToShortest(double value, StringBuilder* result_builder) const {
216 return ToShortestIeeeNumber(value, result_builder, SHORTEST);
217 }
218
219 // Same as ToShortest, but for single-precision floats.
220 bool ToShortestSingle(float value, StringBuilder* result_builder) const {
221 return ToShortestIeeeNumber(value, result_builder, SHORTEST_SINGLE);
222 }
223
224
225 // Computes a decimal representation with a fixed number of digits after the
226 // decimal point. The last emitted digit is rounded.
227 //
228 // Examples:
229 // ToFixed(3.12, 1) -> "3.1"
230 // ToFixed(3.1415, 3) -> "3.142"
231 // ToFixed(1234.56789, 4) -> "1234.5679"
232 // ToFixed(1.23, 5) -> "1.23000"
233 // ToFixed(0.1, 4) -> "0.1000"
234 // ToFixed(1e30, 2) -> "1000000000000000019884624838656.00"
235 // ToFixed(0.1, 30) -> "0.100000000000000005551115123126"
236 // ToFixed(0.1, 17) -> "0.10000000000000001"
237 //
238 // If requested_digits equals 0, then the tail of the result depends on
239 // the EMIT_TRAILING_DECIMAL_POINT and EMIT_TRAILING_ZERO_AFTER_POINT.
240 // Examples, for requested_digits == 0,
241 // let EMIT_TRAILING_DECIMAL_POINT and EMIT_TRAILING_ZERO_AFTER_POINT be
242 // - false and false: then 123.45 -> 123
243 // 0.678 -> 1
244 // - true and false: then 123.45 -> 123.
245 // 0.678 -> 1.
246 // - true and true: then 123.45 -> 123.0
247 // 0.678 -> 1.0
248 //
249 // Returns true if the conversion succeeds. The conversion always succeeds
250 // except for the following cases:
251 // - the input value is special and no infinity_symbol or nan_symbol has
252 // been provided to the constructor,
253 // - 'value' > 10^kMaxFixedDigitsBeforePoint, or
254 // - 'requested_digits' > kMaxFixedDigitsAfterPoint.
255 // The last two conditions imply that the result for non-special values never
256 // contains more than
257 // 1 + kMaxFixedDigitsBeforePoint + 1 + kMaxFixedDigitsAfterPoint characters
258 // (one additional character for the sign, and one for the decimal point).
259 // In addition, the buffer must be able to hold the trailing '\0' character.
260 bool ToFixed(double value,
261 int requested_digits,
262 StringBuilder* result_builder) const;
263
264 // Computes a representation in exponential format with requested_digits
265 // after the decimal point. The last emitted digit is rounded.
266 // If requested_digits equals -1, then the shortest exponential representation
267 // is computed.
268 //
269 // Examples with EMIT_POSITIVE_EXPONENT_SIGN deactivated, and
270 // exponent_character set to 'e'.
271 // ToExponential(3.12, 1) -> "3.1e0"
272 // ToExponential(5.0, 3) -> "5.000e0"
273 // ToExponential(0.001, 2) -> "1.00e-3"
274 // ToExponential(3.1415, -1) -> "3.1415e0"
275 // ToExponential(3.1415, 4) -> "3.1415e0"
276 // ToExponential(3.1415, 3) -> "3.142e0"
277 // ToExponential(123456789000000, 3) -> "1.235e14"
278 // ToExponential(1000000000000000019884624838656.0, -1) -> "1e30"
279 // ToExponential(1000000000000000019884624838656.0, 32) ->
280 // "1.00000000000000001988462483865600e30"
281 // ToExponential(1234, 0) -> "1e3"
282 //
283 // Returns true if the conversion succeeds. The conversion always succeeds
284 // except for the following cases:
285 // - the input value is special and no infinity_symbol or nan_symbol has
286 // been provided to the constructor,
287 // - 'requested_digits' > kMaxExponentialDigits.
288 //
289 // The last condition implies that the result never contains more than
290 // kMaxExponentialDigits + 8 characters (the sign, the digit before the
291 // decimal point, the decimal point, the exponent character, the
292 // exponent's sign, and at most 3 exponent digits).
293 // In addition, the buffer must be able to hold the trailing '\0' character.
294 bool ToExponential(double value,
295 int requested_digits,
296 StringBuilder* result_builder) const;
297
298
299 // Computes 'precision' leading digits of the given 'value' and returns them
300 // either in exponential or decimal format, depending on
301 // max_{leading|trailing}_padding_zeroes_in_precision_mode (given to the
302 // constructor).
303 // The last computed digit is rounded.
304 //
305 // Example with max_leading_padding_zeroes_in_precision_mode = 6.
306 // ToPrecision(0.0000012345, 2) -> "0.0000012"
307 // ToPrecision(0.00000012345, 2) -> "1.2e-7"
308 // Similarly the converter may add up to
309 // max_trailing_padding_zeroes_in_precision_mode in precision mode to avoid
310 // returning an exponential representation. A zero added by the
311 // EMIT_TRAILING_ZERO_AFTER_POINT flag is counted for this limit.
312 // Examples for max_trailing_padding_zeroes_in_precision_mode = 1:
313 // ToPrecision(230.0, 2) -> "230"
314 // ToPrecision(230.0, 2) -> "230." with EMIT_TRAILING_DECIMAL_POINT.
315 // ToPrecision(230.0, 2) -> "2.3e2" with EMIT_TRAILING_ZERO_AFTER_POINT.
316 // Examples for max_trailing_padding_zeroes_in_precision_mode = 3, and no
317 // EMIT_TRAILING_ZERO_AFTER_POINT:
318 // ToPrecision(123450.0, 6) -> "123450"
319 // ToPrecision(123450.0, 5) -> "123450"
320 // ToPrecision(123450.0, 4) -> "123500"
321 // ToPrecision(123450.0, 3) -> "123000"
322 // ToPrecision(123450.0, 2) -> "1.2e5"
323 //
324 // Returns true if the conversion succeeds. The conversion always succeeds
325 // except for the following cases:
326 // - the input value is special and no infinity_symbol or nan_symbol has
327 // been provided to the constructor,
328 // - precision < kMinPericisionDigits
329 // - precision > kMaxPrecisionDigits
330 //
331 // The last condition implies that the result never contains more than
332 // kMaxPrecisionDigits + 7 characters (the sign, the decimal point, the
333 // exponent character, the exponent's sign, and at most 3 exponent digits).
334 // In addition, the buffer must be able to hold the trailing '\0' character.
335 bool ToPrecision(double value,
336 int precision,
337 StringBuilder* result_builder) const;
338
339 enum DtoaMode {
340 // Produce the shortest correct representation.
341 // For example the output of 0.299999999999999988897 is (the less accurate
342 // but correct) 0.3.
343 SHORTEST,
344 // Same as SHORTEST, but for single-precision floats.
345 SHORTEST_SINGLE,
346 // Produce a fixed number of digits after the decimal point.
347 // For instance fixed(0.1, 4) becomes 0.1000
348 // If the input number is big, the output will be big.
349 FIXED,
350 // Fixed number of digits (independent of the decimal point).
351 PRECISION
352 };
353
354 // Converts the given double 'v' to digit characters. 'v' must not be NaN,
355 // +Infinity, or -Infinity. In SHORTEST_SINGLE-mode this restriction also
356 // applies to 'v' after it has been casted to a single-precision float. That
357 // is, in this mode static_cast<float>(v) must not be NaN, +Infinity or
358 // -Infinity.
359 //
360 // The result should be interpreted as buffer * 10^(point-length).
361 //
362 // The digits are written to the buffer in the platform's charset, which is
363 // often UTF-8 (with ASCII-range digits) but may be another charset, such
364 // as EBCDIC.
365 //
366 // The output depends on the given mode:
367 // - SHORTEST: produce the least amount of digits for which the internal
368 // identity requirement is still satisfied. If the digits are printed
369 // (together with the correct exponent) then reading this number will give
370 // 'v' again. The buffer will choose the representation that is closest to
371 // 'v'. If there are two at the same distance, than the one farther away
372 // from 0 is chosen (halfway cases - ending with 5 - are rounded up).
373 // In this mode the 'requested_digits' parameter is ignored.
374 // - SHORTEST_SINGLE: same as SHORTEST but with single-precision.
375 // - FIXED: produces digits necessary to print a given number with
376 // 'requested_digits' digits after the decimal point. The produced digits
377 // might be too short in which case the caller has to fill the remainder
378 // with '0's.
379 // Example: toFixed(0.001, 5) is allowed to return buffer="1", point=-2.
380 // Halfway cases are rounded towards +/-Infinity (away from 0). The call
381 // toFixed(0.15, 2) thus returns buffer="2", point=0.
382 // The returned buffer may contain digits that would be truncated from the
383 // shortest representation of the input.
384 // - PRECISION: produces 'requested_digits' where the first digit is not '0'.
385 // Even though the length of produced digits usually equals
386 // 'requested_digits', the function is allowed to return fewer digits, in
387 // which case the caller has to fill the missing digits with '0's.
388 // Halfway cases are again rounded away from 0.
389 // DoubleToAscii expects the given buffer to be big enough to hold all
390 // digits and a terminating null-character. In SHORTEST-mode it expects a
391 // buffer of at least kBase10MaximalLength + 1. In all other modes the
392 // requested_digits parameter and the padding-zeroes limit the size of the
393 // output. Don't forget the decimal point, the exponent character and the
394 // terminating null-character when computing the maximal output size.
395 // The given length is only used in debug mode to ensure the buffer is big
396 // enough.
397 static void DoubleToAscii(double v,
398 DtoaMode mode,
399 int requested_digits,
400 char* buffer,
401 int buffer_length,
402 bool* sign,
403 int* length,
404 int* point);
405
406 private:
407 // Implementation for ToShortest and ToShortestSingle.
408 bool ToShortestIeeeNumber(double value,
409 StringBuilder* result_builder,
410 DtoaMode mode) const;
411
412 // If the value is a special value (NaN or Infinity) constructs the
413 // corresponding string using the configured infinity/nan-symbol.
414 // If either of them is NULL or the value is not special then the
415 // function returns false.
416 bool HandleSpecialValues(double value, StringBuilder* result_builder) const;
417 // Constructs an exponential representation (i.e. 1.234e56).
418 // The given exponent assumes a decimal point after the first decimal digit.
419 void CreateExponentialRepresentation(const char* decimal_digits,
420 int length,
421 int exponent,
422 StringBuilder* result_builder) const;
423 // Creates a decimal representation (i.e 1234.5678).
424 void CreateDecimalRepresentation(const char* decimal_digits,
425 int length,
426 int decimal_point,
427 int digits_after_point,
428 StringBuilder* result_builder) const;
429
430 const int flags_;
431 const char* const infinity_symbol_;
432 const char* const nan_symbol_;
433 const char exponent_character_;
434 const int decimal_in_shortest_low_;
435 const int decimal_in_shortest_high_;
436 const int max_leading_padding_zeroes_in_precision_mode_;
437 const int max_trailing_padding_zeroes_in_precision_mode_;
438 const int min_exponent_width_;
439
440 DOUBLE_CONVERSION_DISALLOW_IMPLICIT_CONSTRUCTORS(DoubleToStringConverter);
441};
442
443} // namespace double_conversion
444
445#endif // DOUBLE_CONVERSION_DOUBLE_TO_STRING_H_
446