2 * Copyright 2015 Facebook, Inc.
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
8 * http://www.apache.org/licenses/LICENSE-2.0
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
18 * Converts anything to anything, with an emphasis on performance and
21 * @author Andrei Alexandrescu (andrei.alexandrescu@fb.com)
24 #ifndef FOLLY_BASE_CONV_H_
25 #define FOLLY_BASE_CONV_H_
27 #include <folly/FBString.h>
28 #include <folly/Likely.h>
29 #include <folly/Preprocessor.h>
30 #include <folly/Range.h>
32 #include <boost/implicit_cast.hpp>
34 #include <type_traits>
43 // V8 JavaScript implementation
44 #include <double-conversion/double-conversion.h>
46 #define FOLLY_RANGE_CHECK_STRINGIZE(x) #x
47 #define FOLLY_RANGE_CHECK_STRINGIZE2(x) FOLLY_RANGE_CHECK_STRINGIZE(x)
49 // Android doesn't support std::to_string so just use a placeholder there.
51 #define FOLLY_RANGE_CHECK_TO_STRING(x) std::string("N/A")
53 #define FOLLY_RANGE_CHECK_TO_STRING(x) std::to_string(x)
56 #define FOLLY_RANGE_CHECK(condition, message, src) \
57 ((condition) ? (void)0 : throw std::range_error( \
58 (std::string(__FILE__ "(" FOLLY_RANGE_CHECK_STRINGIZE2(__LINE__) "): ") \
59 + (message) + ": '" + (src) + "'").c_str()))
61 #define FOLLY_RANGE_CHECK_BEGIN_END(condition, message, b, e) \
62 FOLLY_RANGE_CHECK(condition, message, std::string((b), (e) - (b)))
64 #define FOLLY_RANGE_CHECK_STRINGPIECE(condition, message, sp) \
65 FOLLY_RANGE_CHECK(condition, message, std::string((sp).data(), (sp).size()))
70 * The identity conversion function.
71 * to<T>(T) returns itself for all types T.
73 template <class Tgt, class Src>
74 typename std::enable_if<std::is_same<Tgt, Src>::value, Tgt>::type
75 to(const Src & value) {
79 template <class Tgt, class Src>
80 typename std::enable_if<std::is_same<Tgt, Src>::value, Tgt>::type
82 return std::move(value);
85 /*******************************************************************************
86 * Integral to integral
87 ******************************************************************************/
90 * Unchecked conversion from integral to boolean. This is different from the
91 * other integral conversions because we use the C convention of treating any
92 * non-zero value as true, instead of range checking.
94 template <class Tgt, class Src>
95 typename std::enable_if<
96 std::is_integral<Src>::value
97 && !std::is_same<Tgt, Src>::value
98 && std::is_same<Tgt, bool>::value,
100 to(const Src & value) {
105 * Checked conversion from integral to integral. The checks are only
106 * performed when meaningful, e.g. conversion from int to long goes
109 template <class Tgt, class Src>
110 typename std::enable_if<
111 std::is_integral<Src>::value
112 && !std::is_same<Tgt, Src>::value
113 && !std::is_same<Tgt, bool>::value
114 && std::is_integral<Tgt>::value,
116 to(const Src & value) {
117 /* static */ if (std::numeric_limits<Tgt>::max()
118 < std::numeric_limits<Src>::max()) {
120 (!greater_than<Tgt, std::numeric_limits<Tgt>::max()>(value)),
122 FOLLY_RANGE_CHECK_TO_STRING(value));
124 /* static */ if (std::is_signed<Src>::value &&
125 (!std::is_signed<Tgt>::value || sizeof(Src) > sizeof(Tgt))) {
127 (!less_than<Tgt, std::numeric_limits<Tgt>::min()>(value)),
129 FOLLY_RANGE_CHECK_TO_STRING(value));
131 return static_cast<Tgt>(value);
134 /*******************************************************************************
135 * Floating point to floating point
136 ******************************************************************************/
138 template <class Tgt, class Src>
139 typename std::enable_if<
140 std::is_floating_point<Tgt>::value
141 && std::is_floating_point<Src>::value
142 && !std::is_same<Tgt, Src>::value,
144 to(const Src & value) {
145 /* static */ if (std::numeric_limits<Tgt>::max() <
146 std::numeric_limits<Src>::max()) {
147 FOLLY_RANGE_CHECK(value <= std::numeric_limits<Tgt>::max(),
149 FOLLY_RANGE_CHECK_TO_STRING(value));
150 FOLLY_RANGE_CHECK(value >= -std::numeric_limits<Tgt>::max(),
152 FOLLY_RANGE_CHECK_TO_STRING(value));
154 return boost::implicit_cast<Tgt>(value);
157 /*******************************************************************************
159 ******************************************************************************/
164 const T& getLastElement(const T & v) {
168 template <class T, class... Ts>
169 typename std::tuple_element<
171 std::tuple<T, Ts...> >::type const&
172 getLastElement(const T&, const Ts&... vs) {
173 return getLastElement(vs...);
176 // This class exists to specialize away std::tuple_element in the case where we
177 // have 0 template arguments. Without this, Clang/libc++ will blow a
178 // static_assert even if tuple_element is protected by an enable_if.
179 template <class... Ts>
180 struct last_element {
181 typedef typename std::enable_if<
183 typename std::tuple_element<
184 sizeof...(Ts) - 1, std::tuple<Ts...>
189 struct last_element<> {
193 } // namespace detail
195 /*******************************************************************************
196 * Conversions from integral types to string types.
197 ******************************************************************************/
199 #if FOLLY_HAVE_INT128_T
202 template <typename IntegerType>
203 constexpr unsigned int
205 return (unsigned int)(ceil(sizeof(IntegerType) * CHAR_BIT * M_LN2 / M_LN10));
209 unsafeTelescope128(char * buffer, size_t room, unsigned __int128 x) {
210 typedef unsigned __int128 Usrc;
213 while (x >= (Usrc(1) << 64)) { // Using 128-bit division while needed
214 const auto y = x / 10;
215 const auto digit = x % 10;
217 buffer[p--] = '0' + digit;
221 uint64_t xx = x; // Moving to faster 64-bit division thereafter
224 const auto y = xx / 10ULL;
225 const auto digit = xx % 10ULL;
227 buffer[p--] = '0' + digit;
231 buffer[p] = '0' + xx;
240 * Returns the number of digits in the base 10 representation of an
241 * uint64_t. Useful for preallocating buffers and such. It's also used
242 * internally, see below. Measurements suggest that defining a
243 * separate overload for 32-bit integers is not worthwhile.
246 inline uint32_t digits10(uint64_t v) {
249 // For this arch we can get a little help from specialized CPU instructions
250 // which can count leading zeroes; 64 minus that is appx. log (base 2).
251 // Use that to approximate base-10 digits (log_10) and then adjust if needed.
253 // 10^i, defined for i 0 through 19.
254 // This is 20 * 8 == 160 bytes, which fits neatly into 5 cache lines
255 // (assuming a cache line size of 64).
256 static const uint64_t powersOf10[20] FOLLY_ALIGNED(64) = {
257 1, 10, 100, 1000, 10000, 100000, 1000000, 10000000, 100000000, 1000000000,
258 10000000000, 100000000000, 1000000000000, 10000000000000, 100000000000000,
259 1000000000000000, 10000000000000000, 100000000000000000,
260 1000000000000000000, 10000000000000000000UL
263 // "count leading zeroes" operation not valid; for 0; special case this.
268 // bits is in the ballpark of log_2(v).
269 const uint8_t leadingZeroes = __builtin_clzll(v);
270 const auto bits = 63 - leadingZeroes;
272 // approximate log_10(v) == log_10(2) * bits.
273 // Integer magic below: 77/256 is appx. 0.3010 (log_10(2)).
274 // The +1 is to make this the ceiling of the log_10 estimate.
275 const uint32_t minLength = 1 + ((bits * 77) >> 8);
277 // return that log_10 lower bound, plus adjust if input >= 10^(that bound)
278 // in case there's a small error and we misjudged length.
279 return minLength + (uint32_t) (UNLIKELY (v >= powersOf10[minLength]));
285 if (LIKELY(v < 10)) return result;
286 if (LIKELY(v < 100)) return result + 1;
287 if (LIKELY(v < 1000)) return result + 2;
288 if (LIKELY(v < 10000)) return result + 3;
289 // Skip ahead by 4 orders of magnitude
298 * Copies the ASCII base 10 representation of v into buffer and
299 * returns the number of bytes written. Does NOT append a \0. Assumes
300 * the buffer points to digits10(v) bytes of valid memory. Note that
301 * uint64 needs at most 20 bytes, uint32_t needs at most 10 bytes,
302 * uint16_t needs at most 5 bytes, and so on. Measurements suggest
303 * that defining a separate overload for 32-bit integers is not
306 * This primitive is unsafe because it makes the size assumption and
307 * because it does not add a terminating \0.
310 inline uint32_t uint64ToBufferUnsafe(uint64_t v, char *const buffer) {
311 auto const result = digits10(v);
312 // WARNING: using size_t or pointer arithmetic for pos slows down
313 // the loop below 20x. This is because several 32-bit ops can be
314 // done in parallel, but only fewer 64-bit ones.
315 uint32_t pos = result - 1;
317 // Keep these together so a peephole optimization "sees" them and
318 // computes them in one shot.
319 auto const q = v / 10;
320 auto const r = static_cast<uint32_t>(v % 10);
321 buffer[pos--] = '0' + r;
324 // Last digit is trivial to handle
325 buffer[pos] = static_cast<uint32_t>(v) + '0';
330 * A single char gets appended.
333 void toAppend(char value, Tgt * result) {
338 constexpr typename std::enable_if<
339 std::is_same<T, char>::value,
341 estimateSpaceNeeded(T) {
346 * Ubiquitous helper template for writing string appenders
348 template <class T> struct IsSomeString {
349 enum { value = std::is_same<T, std::string>::value
350 || std::is_same<T, fbstring>::value };
354 * Everything implicitly convertible to const char* gets appended.
356 template <class Tgt, class Src>
357 typename std::enable_if<
358 std::is_convertible<Src, const char*>::value
359 && IsSomeString<Tgt>::value>::type
360 toAppend(Src value, Tgt * result) {
361 // Treat null pointers like an empty string, as in:
362 // operator<<(std::ostream&, const char*).
363 const char* c = value;
365 result->append(value);
370 typename std::enable_if<
371 std::is_convertible<Src, const char*>::value,
373 estimateSpaceNeeded(Src value) {
374 const char *c = value;
376 return folly::StringPiece(value).size();
382 typename std::enable_if<
383 (std::is_convertible<Src, folly::StringPiece>::value ||
384 IsSomeString<Src>::value) &&
385 !std::is_convertible<Src, const char*>::value,
387 estimateSpaceNeeded(Src value) {
388 return folly::StringPiece(value).size();
392 inline size_t estimateSpaceNeeded(std::nullptr_t value) {
397 typename std::enable_if<
398 std::is_pointer<Src>::value &&
399 IsSomeString<std::remove_pointer<Src>>::value,
401 estimateSpaceNeeded(Src value) {
402 return value->size();
406 * Strings get appended, too.
408 template <class Tgt, class Src>
409 typename std::enable_if<
410 IsSomeString<Src>::value && IsSomeString<Tgt>::value>::type
411 toAppend(const Src& value, Tgt * result) {
412 result->append(value);
416 * and StringPiece objects too
419 typename std::enable_if<
420 IsSomeString<Tgt>::value>::type
421 toAppend(StringPiece value, Tgt * result) {
422 result->append(value.data(), value.size());
426 * There's no implicit conversion from fbstring to other string types,
427 * so make a specialization.
430 typename std::enable_if<
431 IsSomeString<Tgt>::value>::type
432 toAppend(const fbstring& value, Tgt * result) {
433 result->append(value.data(), value.size());
436 #if FOLLY_HAVE_INT128_T
438 * Special handling for 128 bit integers.
443 toAppend(__int128 value, Tgt * result) {
444 typedef unsigned __int128 Usrc;
445 char buffer[detail::digitsEnough<unsigned __int128>() + 1];
449 p = detail::unsafeTelescope128(buffer, sizeof(buffer), Usrc(-value));
452 p = detail::unsafeTelescope128(buffer, sizeof(buffer), value);
455 result->append(buffer + p, buffer + sizeof(buffer));
460 toAppend(unsigned __int128 value, Tgt * result) {
461 char buffer[detail::digitsEnough<unsigned __int128>()];
464 p = detail::unsafeTelescope128(buffer, sizeof(buffer), value);
466 result->append(buffer + p, buffer + sizeof(buffer));
470 constexpr typename std::enable_if<
471 std::is_same<T, __int128>::value,
473 estimateSpaceNeeded(T) {
474 return detail::digitsEnough<__int128>();
478 constexpr typename std::enable_if<
479 std::is_same<T, unsigned __int128>::value,
481 estimateSpaceNeeded(T) {
482 return detail::digitsEnough<unsigned __int128>();
488 * int32_t and int64_t to string (by appending) go through here. The
489 * result is APPENDED to a preexisting string passed as the second
490 * parameter. This should be efficient with fbstring because fbstring
491 * incurs no dynamic allocation below 23 bytes and no number has more
492 * than 22 bytes in its textual representation (20 for digits, one for
493 * sign, one for the terminating 0).
495 template <class Tgt, class Src>
496 typename std::enable_if<
497 std::is_integral<Src>::value && std::is_signed<Src>::value &&
498 IsSomeString<Tgt>::value && sizeof(Src) >= 4>::type
499 toAppend(Src value, Tgt * result) {
502 result->push_back('-');
503 result->append(buffer, uint64ToBufferUnsafe(-uint64_t(value), buffer));
505 result->append(buffer, uint64ToBufferUnsafe(value, buffer));
510 typename std::enable_if<
511 std::is_integral<Src>::value && std::is_signed<Src>::value
512 && sizeof(Src) >= 4 && sizeof(Src) < 16,
514 estimateSpaceNeeded(Src value) {
516 // When "value" is the smallest negative, negating it would evoke
517 // undefined behavior, so, instead of writing "-value" below, we write
518 // "~static_cast<uint64_t>(value) + 1"
519 return 1 + digits10(~static_cast<uint64_t>(value) + 1);
522 return digits10(static_cast<uint64_t>(value));
526 * As above, but for uint32_t and uint64_t.
528 template <class Tgt, class Src>
529 typename std::enable_if<
530 std::is_integral<Src>::value && !std::is_signed<Src>::value
531 && IsSomeString<Tgt>::value && sizeof(Src) >= 4>::type
532 toAppend(Src value, Tgt * result) {
534 result->append(buffer, buffer + uint64ToBufferUnsafe(value, buffer));
538 typename std::enable_if<
539 std::is_integral<Src>::value && !std::is_signed<Src>::value
540 && sizeof(Src) >= 4 && sizeof(Src) < 16,
542 estimateSpaceNeeded(Src value) {
543 return digits10(value);
547 * All small signed and unsigned integers to string go through 32-bit
548 * types int32_t and uint32_t, respectively.
550 template <class Tgt, class Src>
551 typename std::enable_if<
552 std::is_integral<Src>::value
553 && IsSomeString<Tgt>::value && sizeof(Src) < 4>::type
554 toAppend(Src value, Tgt * result) {
556 std::conditional<std::is_signed<Src>::value, int64_t, uint64_t>::type
558 toAppend<Tgt>(static_cast<Intermediate>(value), result);
562 typename std::enable_if<
563 std::is_integral<Src>::value
565 && !std::is_same<Src, char>::value,
567 estimateSpaceNeeded(Src value) {
569 std::conditional<std::is_signed<Src>::value, int64_t, uint64_t>::type
571 return estimateSpaceNeeded(static_cast<Intermediate>(value));
575 * Enumerated values get appended as integers.
577 template <class Tgt, class Src>
578 typename std::enable_if<
579 std::is_enum<Src>::value && IsSomeString<Tgt>::value>::type
580 toAppend(Src value, Tgt * result) {
582 static_cast<typename std::underlying_type<Src>::type>(value), result);
586 typename std::enable_if<
587 std::is_enum<Src>::value, size_t>::type
588 estimateSpaceNeeded(Src value) {
589 return estimateSpaceNeeded(
590 static_cast<typename std::underlying_type<Src>::type>(value));
593 /*******************************************************************************
594 * Conversions from floating-point types to string types.
595 ******************************************************************************/
598 constexpr int kConvMaxDecimalInShortestLow = -6;
599 constexpr int kConvMaxDecimalInShortestHigh = 21;
602 /** Wrapper around DoubleToStringConverter **/
603 template <class Tgt, class Src>
604 typename std::enable_if<
605 std::is_floating_point<Src>::value
606 && IsSomeString<Tgt>::value>::type
610 double_conversion::DoubleToStringConverter::DtoaMode mode,
611 unsigned int numDigits) {
612 using namespace double_conversion;
613 DoubleToStringConverter
614 conv(DoubleToStringConverter::NO_FLAGS,
615 "Infinity", "NaN", 'E',
616 detail::kConvMaxDecimalInShortestLow,
617 detail::kConvMaxDecimalInShortestHigh,
618 6, // max leading padding zeros
619 1); // max trailing padding zeros
621 StringBuilder builder(buffer, sizeof(buffer));
623 case DoubleToStringConverter::SHORTEST:
624 conv.ToShortest(value, &builder);
626 case DoubleToStringConverter::FIXED:
627 conv.ToFixed(value, numDigits, &builder);
630 CHECK(mode == DoubleToStringConverter::PRECISION);
631 conv.ToPrecision(value, numDigits, &builder);
634 const size_t length = builder.position();
636 result->append(buffer, length);
640 * As above, but for floating point
642 template <class Tgt, class Src>
643 typename std::enable_if<
644 std::is_floating_point<Src>::value
645 && IsSomeString<Tgt>::value>::type
646 toAppend(Src value, Tgt * result) {
648 value, result, double_conversion::DoubleToStringConverter::SHORTEST, 0);
652 * Upper bound of the length of the output from
653 * DoubleToStringConverter::ToShortest(double, StringBuilder*),
654 * as used in toAppend(double, string*).
657 typename std::enable_if<
658 std::is_floating_point<Src>::value, size_t>::type
659 estimateSpaceNeeded(Src value) {
660 // kBase10MaximalLength is 17. We add 1 for decimal point,
661 // e.g. 10.0/9 is 17 digits and 18 characters, including the decimal point.
662 constexpr int kMaxMantissaSpace =
663 double_conversion::DoubleToStringConverter::kBase10MaximalLength + 1;
664 // strlen("E-") + digits10(numeric_limits<double>::max_exponent10)
665 constexpr int kMaxExponentSpace = 2 + 3;
666 static const int kMaxPositiveSpace = std::max({
667 // E.g. 1.1111111111111111E-100.
668 kMaxMantissaSpace + kMaxExponentSpace,
669 // E.g. 0.000001.1111111111111111, if kConvMaxDecimalInShortestLow is -6.
670 kMaxMantissaSpace - detail::kConvMaxDecimalInShortestLow,
671 // If kConvMaxDecimalInShortestHigh is 21, then 1e21 is the smallest
672 // number > 1 which ToShortest outputs in exponential notation,
673 // so 21 is the longest non-exponential number > 1.
674 detail::kConvMaxDecimalInShortestHigh
676 return kMaxPositiveSpace + (value < 0); // +1 for minus sign, if negative
680 * This can be specialized, together with adding specialization
681 * for estimateSpaceNeed for your type, so that we allocate
682 * as much as you need instead of the default
685 struct HasLengthEstimator : std::false_type {};
688 constexpr typename std::enable_if<
689 !std::is_fundamental<Src>::value
690 #ifdef FOLLY_HAVE_INT128_T
691 // On OSX 10.10, is_fundamental<__int128> is false :-O
692 && !std::is_same<__int128, Src>::value
693 && !std::is_same<unsigned __int128, Src>::value
695 && !IsSomeString<Src>::value
696 && !std::is_convertible<Src, const char*>::value
697 && !std::is_convertible<Src, StringPiece>::value
698 && !std::is_enum<Src>::value
699 && !HasLengthEstimator<Src>::value,
701 estimateSpaceNeeded(const Src&) {
702 return sizeof(Src) + 1; // dumbest best effort ever?
707 inline size_t estimateSpaceToReserve(size_t sofar) {
711 template <class T, class... Ts>
712 size_t estimateSpaceToReserve(size_t sofar, const T& v, const Ts&... vs) {
713 return estimateSpaceToReserve(sofar + estimateSpaceNeeded(v), vs...);
717 size_t estimateSpaceToReserve(size_t sofar, const T& v) {
718 return sofar + estimateSpaceNeeded(v);
722 void reserveInTarget(const Ts&...vs) {
723 getLastElement(vs...)->reserve(estimateSpaceToReserve(0, vs...));
726 template<class Delimiter, class...Ts>
727 void reserveInTargetDelim(const Delimiter& d, const Ts&...vs) {
728 static_assert(sizeof...(vs) >= 2, "Needs at least 2 args");
729 size_t fordelim = (sizeof...(vs) - 2) * estimateSpaceToReserve(0, d);
730 getLastElement(vs...)->reserve(estimateSpaceToReserve(fordelim, vs...));
734 * Variadic base case: append one element
736 template <class T, class Tgt>
737 typename std::enable_if<
738 IsSomeString<typename std::remove_pointer<Tgt>::type>
740 toAppendStrImpl(const T& v, Tgt result) {
744 template <class T, class... Ts>
745 typename std::enable_if<sizeof...(Ts) >= 2
747 typename std::remove_pointer<
748 typename detail::last_element<Ts...>::type
749 >::type>::value>::type
750 toAppendStrImpl(const T& v, const Ts&... vs) {
751 toAppend(v, getLastElement(vs...));
752 toAppendStrImpl(vs...);
755 template <class Delimiter, class T, class Tgt>
756 typename std::enable_if<
757 IsSomeString<typename std::remove_pointer<Tgt>::type>
759 toAppendDelimStrImpl(const Delimiter& delim, const T& v, Tgt result) {
763 template <class Delimiter, class T, class... Ts>
764 typename std::enable_if<sizeof...(Ts) >= 2
766 typename std::remove_pointer<
767 typename detail::last_element<Ts...>::type
768 >::type>::value>::type
769 toAppendDelimStrImpl(const Delimiter& delim, const T& v, const Ts&... vs) {
770 // we are really careful here, calling toAppend with just one element does
771 // not try to estimate space needed (as we already did that). If we call
772 // toAppend(v, delim, ....) we would do unnecesary size calculation
773 toAppend(v, detail::getLastElement(vs...));
774 toAppend(delim, detail::getLastElement(vs...));
775 toAppendDelimStrImpl(delim, vs...);
781 * Variadic conversion to string. Appends each element in turn.
782 * If we have two or more things to append, we it will not reserve
783 * the space for them and will depend on strings exponential growth.
784 * If you just append once consider using toAppendFit which reserves
785 * the space needed (but does not have exponential as a result).
787 template <class... Ts>
788 typename std::enable_if<sizeof...(Ts) >= 3
790 typename std::remove_pointer<
791 typename detail::last_element<Ts...>::type
792 >::type>::value>::type
793 toAppend(const Ts&... vs) {
794 ::folly::detail::toAppendStrImpl(vs...);
798 * Special version of the call that preallocates exaclty as much memory
799 * as need for arguments to be stored in target. This means we are
800 * not doing exponential growth when we append. If you are using it
801 * in a loop you are aiming at your foot with a big perf-destroying
803 * On the other hand if you are appending to a string once, this
804 * will probably save a few calls to malloc.
806 template <class... Ts>
807 typename std::enable_if<
809 typename std::remove_pointer<
810 typename detail::last_element<Ts...>::type
811 >::type>::value>::type
812 toAppendFit(const Ts&... vs) {
813 ::folly::detail::reserveInTarget(vs...);
818 void toAppendFit(const Ts&) {}
821 * Variadic base case: do nothing.
824 typename std::enable_if<IsSomeString<Tgt>::value>::type
825 toAppend(Tgt* result) {
829 * Variadic base case: do nothing.
831 template <class Delimiter, class Tgt>
832 typename std::enable_if<IsSomeString<Tgt>::value>::type
833 toAppendDelim(const Delimiter& delim, Tgt* result) {
837 * 1 element: same as toAppend.
839 template <class Delimiter, class T, class Tgt>
840 typename std::enable_if<IsSomeString<Tgt>::value>::type
841 toAppendDelim(const Delimiter& delim, const T& v, Tgt* tgt) {
846 * Append to string with a delimiter in between elements. Check out
847 * comments for toAppend for details about memory allocation.
849 template <class Delimiter, class... Ts>
850 typename std::enable_if<sizeof...(Ts) >= 3
852 typename std::remove_pointer<
853 typename detail::last_element<Ts...>::type
854 >::type>::value>::type
855 toAppendDelim(const Delimiter& delim, const Ts&... vs) {
856 detail::toAppendDelimStrImpl(delim, vs...);
860 * Detail in comment for toAppendFit
862 template <class Delimiter, class... Ts>
863 typename std::enable_if<
865 typename std::remove_pointer<
866 typename detail::last_element<Ts...>::type
867 >::type>::value>::type
868 toAppendDelimFit(const Delimiter& delim, const Ts&... vs) {
869 detail::reserveInTargetDelim(delim, vs...);
870 toAppendDelim(delim, vs...);
873 template <class De, class Ts>
874 void toAppendDelimFit(const De&, const Ts&) {}
877 * to<SomeString>(v1, v2, ...) uses toAppend() (see below) as back-end
880 template <class Tgt, class... Ts>
881 typename std::enable_if<
882 IsSomeString<Tgt>::value && (
883 sizeof...(Ts) != 1 ||
884 !std::is_same<Tgt, typename detail::last_element<Ts...>::type>::value),
886 to(const Ts&... vs) {
888 toAppendFit(vs..., &result);
893 * toDelim<SomeString>(SomeString str) returns itself.
895 template <class Tgt, class Delim, class Src>
896 typename std::enable_if<
897 IsSomeString<Tgt>::value && std::is_same<Tgt, Src>::value,
899 toDelim(const Delim& delim, const Src & value) {
904 * toDelim<SomeString>(delim, v1, v2, ...) uses toAppendDelim() as
905 * back-end for all types.
907 template <class Tgt, class Delim, class... Ts>
908 typename std::enable_if<
909 IsSomeString<Tgt>::value && (
910 sizeof...(Ts) != 1 ||
911 !std::is_same<Tgt, typename detail::last_element<Ts...>::type>::value),
913 toDelim(const Delim& delim, const Ts&... vs) {
915 toAppendDelimFit(delim, vs..., &result);
919 /*******************************************************************************
920 * Conversions from string types to integral types.
921 ******************************************************************************/
926 * Finds the first non-digit in a string. The number of digits
927 * searched depends on the precision of the Tgt integral. Assumes the
928 * string starts with NO whitespace and NO sign.
930 * The semantics of the routine is:
932 * if (b >= e || !isdigit(*b)) return b;
935 * Complete unrolling marks bottom-line (i.e. entire conversion)
936 * improvements of 20%.
939 const char* findFirstNonDigit(const char* b, const char* e) {
941 auto const c = static_cast<unsigned>(*b) - '0';
947 // Maximum value of number when represented as a string
948 template <class T> struct MaxString {
949 static const char*const value;
952 bool str_to_bool(StringPiece* src);
955 Tgt digits_to(const char* b, const char* e);
957 extern template unsigned char digits_to<unsigned char>(const char* b,
959 extern template unsigned short digits_to<unsigned short>(const char* b,
961 extern template unsigned int digits_to<unsigned int>(const char* b,
963 extern template unsigned long digits_to<unsigned long>(const char* b,
965 extern template unsigned long long digits_to<unsigned long long>(
966 const char* b, const char* e);
967 #if FOLLY_HAVE_INT128_T
968 extern template unsigned __int128 digits_to<unsigned __int128>(const char* b,
972 } // namespace detail
975 * String represented as a pair of pointers to char to unsigned
976 * integrals. Assumes NO whitespace before or after.
979 typename std::enable_if<
980 std::is_integral<Tgt>::value && !std::is_signed<Tgt>::value
981 && !std::is_same<typename std::remove_cv<Tgt>::type, bool>::value,
983 to(const char * b, const char * e) {
984 return detail::digits_to<Tgt>(b, e);
988 * String represented as a pair of pointers to char to signed
989 * integrals. Assumes NO whitespace before or after. Allows an
990 * optional leading sign.
993 typename std::enable_if<
994 std::is_integral<Tgt>::value && std::is_signed<Tgt>::value,
996 to(const char * b, const char * e) {
997 FOLLY_RANGE_CHECK(b < e, "Empty input string in conversion to integral",
998 to<std::string>("b: ", intptr_t(b), " e: ", intptr_t(e)));
1001 Tgt result = -to<typename std::make_unsigned<Tgt>::type>(b + 1, e);
1002 FOLLY_RANGE_CHECK_BEGIN_END(result <= 0, "Negative overflow.", b, e);
1005 FOLLY_RANGE_CHECK_BEGIN_END(*b == '+', "Invalid lead character", b, e);
1008 Tgt result = to<typename std::make_unsigned<Tgt>::type>(b, e);
1009 FOLLY_RANGE_CHECK_BEGIN_END(result >= 0, "Overflow", b, e);
1014 * Parsing strings to integrals. These routines differ from
1015 * to<integral>(string) in that they take a POINTER TO a StringPiece
1016 * and alter that StringPiece to reflect progress information.
1020 * StringPiece to integrals, with progress information. Alters the
1021 * StringPiece parameter to munch the already-parsed characters.
1023 template <class Tgt>
1024 typename std::enable_if<
1025 std::is_integral<Tgt>::value
1026 && !std::is_same<typename std::remove_cv<Tgt>::type, bool>::value,
1028 to(StringPiece * src) {
1030 auto b = src->data(), past = src->data() + src->size();
1032 FOLLY_RANGE_CHECK_STRINGPIECE(b < past,
1033 "No digits found in input string", *src);
1034 if (!isspace(*b)) break;
1039 // First digit is customized because we test for sign
1040 bool negative = false;
1041 /* static */ if (std::is_signed<Tgt>::value) {
1046 FOLLY_RANGE_CHECK_STRINGPIECE(*m == '+', "Invalid leading character in "
1047 "conversion to integral", *src);
1053 FOLLY_RANGE_CHECK_STRINGPIECE(m < past, "No digits found in input string",
1055 FOLLY_RANGE_CHECK_STRINGPIECE(isdigit(*m), "Non-digit character found", *src);
1056 m = detail::findFirstNonDigit<Tgt>(m + 1, past);
1059 /* static */ if (!std::is_signed<Tgt>::value) {
1060 result = detail::digits_to<typename std::make_unsigned<Tgt>::type>(b, m);
1062 auto t = detail::digits_to<typename std::make_unsigned<Tgt>::type>(b, m);
1065 FOLLY_RANGE_CHECK_STRINGPIECE(is_non_positive(result),
1066 "Negative overflow", *src);
1069 FOLLY_RANGE_CHECK_STRINGPIECE(is_non_negative(result), "Overflow", *src);
1072 src->advance(m - src->data());
1077 * StringPiece to bool, with progress information. Alters the
1078 * StringPiece parameter to munch the already-parsed characters.
1080 template <class Tgt>
1081 typename std::enable_if<
1082 std::is_same<typename std::remove_cv<Tgt>::type, bool>::value,
1084 to(StringPiece * src) {
1085 return detail::str_to_bool(src);
1091 * Enforce that the suffix following a number is made up only of whitespace.
1093 inline void enforceWhitespace(const char* b, const char* e) {
1094 for (; b != e; ++b) {
1095 FOLLY_RANGE_CHECK_BEGIN_END(isspace(*b),
1096 to<std::string>("Non-whitespace: ", *b),
1101 } // namespace detail
1104 * String or StringPiece to integrals. Accepts leading and trailing
1105 * whitespace, but no non-space trailing characters.
1107 template <class Tgt>
1108 typename std::enable_if<
1109 std::is_integral<Tgt>::value,
1111 to(StringPiece src) {
1112 Tgt result = to<Tgt>(&src);
1113 detail::enforceWhitespace(src.data(), src.data() + src.size());
1117 /*******************************************************************************
1118 * Conversions from string types to floating-point types.
1119 ******************************************************************************/
1122 * StringPiece to double, with progress information. Alters the
1123 * StringPiece parameter to munch the already-parsed characters.
1125 template <class Tgt>
1126 inline typename std::enable_if<
1127 std::is_floating_point<Tgt>::value,
1129 to(StringPiece *const src) {
1130 using namespace double_conversion;
1131 static StringToDoubleConverter
1132 conv(StringToDoubleConverter::ALLOW_TRAILING_JUNK
1133 | StringToDoubleConverter::ALLOW_LEADING_SPACES,
1135 // return this for junk input string
1136 std::numeric_limits<double>::quiet_NaN(),
1139 FOLLY_RANGE_CHECK_STRINGPIECE(!src->empty(),
1140 "No digits found in input string", *src);
1143 auto result = conv.StringToDouble(src->data(),
1144 static_cast<int>(src->size()),
1145 &length); // processed char count
1147 if (!std::isnan(result)) {
1148 src->advance(length);
1152 for (;; src->advance(1)) {
1154 throw std::range_error("Unable to convert an empty string"
1155 " to a floating point value.");
1157 if (!isspace(src->front())) {
1162 // Was that "inf[inity]"?
1163 if (src->size() >= 3 && toupper((*src)[0]) == 'I'
1164 && toupper((*src)[1]) == 'N' && toupper((*src)[2]) == 'F') {
1165 if (src->size() >= 8 &&
1166 toupper((*src)[3]) == 'I' &&
1167 toupper((*src)[4]) == 'N' &&
1168 toupper((*src)[5]) == 'I' &&
1169 toupper((*src)[6]) == 'T' &&
1170 toupper((*src)[7]) == 'Y') {
1175 return std::numeric_limits<Tgt>::infinity();
1178 // Was that "-inf[inity]"?
1179 if (src->size() >= 4 && toupper((*src)[0]) == '-'
1180 && toupper((*src)[1]) == 'I' && toupper((*src)[2]) == 'N'
1181 && toupper((*src)[3]) == 'F') {
1182 if (src->size() >= 9 &&
1183 toupper((*src)[4]) == 'I' &&
1184 toupper((*src)[5]) == 'N' &&
1185 toupper((*src)[6]) == 'I' &&
1186 toupper((*src)[7]) == 'T' &&
1187 toupper((*src)[8]) == 'Y') {
1192 return -std::numeric_limits<Tgt>::infinity();
1196 if (src->size() >= 3 && toupper((*src)[0]) == 'N'
1197 && toupper((*src)[1]) == 'A' && toupper((*src)[2]) == 'N') {
1199 return std::numeric_limits<Tgt>::quiet_NaN();
1203 if (src->size() >= 4 &&
1204 toupper((*src)[0]) == '-' &&
1205 toupper((*src)[1]) == 'N' &&
1206 toupper((*src)[2]) == 'A' &&
1207 toupper((*src)[3]) == 'N') {
1209 return -std::numeric_limits<Tgt>::quiet_NaN();
1213 throw std::range_error("Unable to convert \"" + src->toString()
1214 + "\" to a floating point value.");
1218 * Any string, const char*, or StringPiece to double.
1220 template <class Tgt>
1221 typename std::enable_if<
1222 std::is_floating_point<Tgt>::value,
1224 to(StringPiece src) {
1225 Tgt result = Tgt(to<double>(&src));
1226 detail::enforceWhitespace(src.data(), src.data() + src.size());
1230 /*******************************************************************************
1231 * Integral to floating point and back
1232 ******************************************************************************/
1235 * Checked conversion from integral to floating point and back. The
1236 * result must be convertible back to the source type without loss of
1237 * precision. This seems Draconian but sometimes is what's needed, and
1238 * complements existing routines nicely. For various rounding
1239 * routines, see <math>.
1241 template <class Tgt, class Src>
1242 typename std::enable_if<
1243 (std::is_integral<Src>::value && std::is_floating_point<Tgt>::value)
1245 (std::is_floating_point<Src>::value && std::is_integral<Tgt>::value),
1247 to(const Src & value) {
1248 Tgt result = Tgt(value);
1249 auto witness = static_cast<Src>(result);
1250 if (value != witness) {
1251 throw std::range_error(
1252 to<std::string>("to<>: loss of precision when converting ", value,
1253 #ifdef FOLLY_HAS_RTTI
1254 " to type ", typeid(Tgt).name()
1263 /*******************************************************************************
1264 * Enum to anything and back
1265 ******************************************************************************/
1267 template <class Tgt, class Src>
1268 typename std::enable_if<
1269 std::is_enum<Src>::value && !std::is_same<Src, Tgt>::value, Tgt>::type
1270 to(const Src & value) {
1271 return to<Tgt>(static_cast<typename std::underlying_type<Src>::type>(value));
1274 template <class Tgt, class Src>
1275 typename std::enable_if<
1276 std::is_enum<Tgt>::value && !std::is_same<Src, Tgt>::value, Tgt>::type
1277 to(const Src & value) {
1278 return static_cast<Tgt>(to<typename std::underlying_type<Tgt>::type>(value));
1281 } // namespace folly
1283 // FOLLY_CONV_INTERNAL is defined by Conv.cpp. Keep the FOLLY_RANGE_CHECK
1284 // macro for use in Conv.cpp, but #undefine it everywhere else we are included,
1285 // to avoid defining this global macro name in other files that include Conv.h.
1286 #ifndef FOLLY_CONV_INTERNAL
1287 #undef FOLLY_RANGE_CHECK
1288 #undef FOLLY_RANGE_CHECK_BEGIN_END
1289 #undef FOLLY_RANGE_CHECK_STRINGPIECE
1290 #undef FOLLY_RANGE_CHECK_STRINGIZE
1291 #undef FOLLY_RANGE_CHECK_STRINGIZE2
1294 #endif /* FOLLY_BASE_CONV_H_ */