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Diffstat (limited to 'third_party/abseil_cpp/absl/strings/internal/str_format/float_conversion.cc')
| -rw-r--r-- | third_party/abseil_cpp/absl/strings/internal/str_format/float_conversion.cc | 1144 |
1 files changed, 0 insertions, 1144 deletions
diff --git a/third_party/abseil_cpp/absl/strings/internal/str_format/float_conversion.cc b/third_party/abseil_cpp/absl/strings/internal/str_format/float_conversion.cc deleted file mode 100644 index 10e4695411..0000000000 --- a/third_party/abseil_cpp/absl/strings/internal/str_format/float_conversion.cc +++ /dev/null @@ -1,1144 +0,0 @@ -#include "absl/strings/internal/str_format/float_conversion.h" - -#include <string.h> - -#include <algorithm> -#include <cassert> -#include <cmath> -#include <limits> -#include <string> - -#include "absl/base/attributes.h" -#include "absl/base/config.h" -#include "absl/base/internal/bits.h" -#include "absl/base/optimization.h" -#include "absl/functional/function_ref.h" -#include "absl/meta/type_traits.h" -#include "absl/numeric/int128.h" -#include "absl/types/optional.h" -#include "absl/types/span.h" - -namespace absl { -ABSL_NAMESPACE_BEGIN -namespace str_format_internal { - -namespace { - -// The code below wants to avoid heap allocations. -// To do so it needs to allocate memory on the stack. -// `StackArray` will allocate memory on the stack in the form of a uint32_t -// array and call the provided callback with said memory. -// It will allocate memory in increments of 512 bytes. We could allocate the -// largest needed unconditionally, but that is more than we need in most of -// cases. This way we use less stack in the common cases. -class StackArray { - using Func = absl::FunctionRef<void(absl::Span<uint32_t>)>; - static constexpr size_t kStep = 512 / sizeof(uint32_t); - // 5 steps is 2560 bytes, which is enough to hold a long double with the - // largest/smallest exponents. - // The operations below will static_assert their particular maximum. - static constexpr size_t kNumSteps = 5; - - // We do not want this function to be inlined. - // Otherwise the caller will allocate the stack space unnecessarily for all - // the variants even though it only calls one. - template <size_t steps> - ABSL_ATTRIBUTE_NOINLINE static void RunWithCapacityImpl(Func f) { - uint32_t values[steps * kStep]{}; - f(absl::MakeSpan(values)); - } - - public: - static constexpr size_t kMaxCapacity = kStep * kNumSteps; - - static void RunWithCapacity(size_t capacity, Func f) { - assert(capacity <= kMaxCapacity); - const size_t step = (capacity + kStep - 1) / kStep; - assert(step <= kNumSteps); - switch (step) { - case 1: - return RunWithCapacityImpl<1>(f); - case 2: - return RunWithCapacityImpl<2>(f); - case 3: - return RunWithCapacityImpl<3>(f); - case 4: - return RunWithCapacityImpl<4>(f); - case 5: - return RunWithCapacityImpl<5>(f); - } - - assert(false && "Invalid capacity"); - } -}; - -// Calculates `10 * (*v) + carry` and stores the result in `*v` and returns -// the carry. -template <typename Int> -inline Int MultiplyBy10WithCarry(Int *v, Int carry) { - using BiggerInt = absl::conditional_t<sizeof(Int) == 4, uint64_t, uint128>; - BiggerInt tmp = 10 * static_cast<BiggerInt>(*v) + carry; - *v = static_cast<Int>(tmp); - return static_cast<Int>(tmp >> (sizeof(Int) * 8)); -} - -// Calculates `(2^64 * carry + *v) / 10`. -// Stores the quotient in `*v` and returns the remainder. -// Requires: `0 <= carry <= 9` -inline uint64_t DivideBy10WithCarry(uint64_t *v, uint64_t carry) { - constexpr uint64_t divisor = 10; - // 2^64 / divisor = chunk_quotient + chunk_remainder / divisor - constexpr uint64_t chunk_quotient = (uint64_t{1} << 63) / (divisor / 2); - constexpr uint64_t chunk_remainder = uint64_t{} - chunk_quotient * divisor; - - const uint64_t mod = *v % divisor; - const uint64_t next_carry = chunk_remainder * carry + mod; - *v = *v / divisor + carry * chunk_quotient + next_carry / divisor; - return next_carry % divisor; -} - -// Generates the decimal representation for an integer of the form `v * 2^exp`, -// where `v` and `exp` are both positive integers. -// It generates the digits from the left (ie the most significant digit first) -// to allow for direct printing into the sink. -// -// Requires `0 <= exp` and `exp <= numeric_limits<long double>::max_exponent`. -class BinaryToDecimal { - static constexpr int ChunksNeeded(int exp) { - // We will left shift a uint128 by `exp` bits, so we need `128+exp` total - // bits. Round up to 32. - // See constructor for details about adding `10%` to the value. - return (128 + exp + 31) / 32 * 11 / 10; - } - - public: - // Run the conversion for `v * 2^exp` and call `f(binary_to_decimal)`. - // This function will allocate enough stack space to perform the conversion. - static void RunConversion(uint128 v, int exp, - absl::FunctionRef<void(BinaryToDecimal)> f) { - assert(exp > 0); - assert(exp <= std::numeric_limits<long double>::max_exponent); - static_assert( - StackArray::kMaxCapacity >= - ChunksNeeded(std::numeric_limits<long double>::max_exponent), - ""); - - StackArray::RunWithCapacity( - ChunksNeeded(exp), - [=](absl::Span<uint32_t> input) { f(BinaryToDecimal(input, v, exp)); }); - } - - int TotalDigits() const { - return static_cast<int>((decimal_end_ - decimal_start_) * kDigitsPerChunk + - CurrentDigits().size()); - } - - // See the current block of digits. - absl::string_view CurrentDigits() const { - return absl::string_view(digits_ + kDigitsPerChunk - size_, size_); - } - - // Advance the current view of digits. - // Returns `false` when no more digits are available. - bool AdvanceDigits() { - if (decimal_start_ >= decimal_end_) return false; - - uint32_t w = data_[decimal_start_++]; - for (size_ = 0; size_ < kDigitsPerChunk; w /= 10) { - digits_[kDigitsPerChunk - ++size_] = w % 10 + '0'; - } - return true; - } - - private: - BinaryToDecimal(absl::Span<uint32_t> data, uint128 v, int exp) : data_(data) { - // We need to print the digits directly into the sink object without - // buffering them all first. To do this we need two things: - // - to know the total number of digits to do padding when necessary - // - to generate the decimal digits from the left. - // - // In order to do this, we do a two pass conversion. - // On the first pass we convert the binary representation of the value into - // a decimal representation in which each uint32_t chunk holds up to 9 - // decimal digits. In the second pass we take each decimal-holding-uint32_t - // value and generate the ascii decimal digits into `digits_`. - // - // The binary and decimal representations actually share the same memory - // region. As we go converting the chunks from binary to decimal we free - // them up and reuse them for the decimal representation. One caveat is that - // the decimal representation is around 7% less efficient in space than the - // binary one. We allocate an extra 10% memory to account for this. See - // ChunksNeeded for this calculation. - int chunk_index = exp / 32; - decimal_start_ = decimal_end_ = ChunksNeeded(exp); - const int offset = exp % 32; - // Left shift v by exp bits. - data_[chunk_index] = static_cast<uint32_t>(v << offset); - for (v >>= (32 - offset); v; v >>= 32) - data_[++chunk_index] = static_cast<uint32_t>(v); - - while (chunk_index >= 0) { - // While we have more than one chunk available, go in steps of 1e9. - // `data_[chunk_index]` holds the highest non-zero binary chunk, so keep - // the variable updated. - uint32_t carry = 0; - for (int i = chunk_index; i >= 0; --i) { - uint64_t tmp = uint64_t{data_[i]} + (uint64_t{carry} << 32); - data_[i] = static_cast<uint32_t>(tmp / uint64_t{1000000000}); - carry = static_cast<uint32_t>(tmp % uint64_t{1000000000}); - } - - // If the highest chunk is now empty, remove it from view. - if (data_[chunk_index] == 0) --chunk_index; - - --decimal_start_; - assert(decimal_start_ != chunk_index); - data_[decimal_start_] = carry; - } - - // Fill the first set of digits. The first chunk might not be complete, so - // handle differently. - for (uint32_t first = data_[decimal_start_++]; first != 0; first /= 10) { - digits_[kDigitsPerChunk - ++size_] = first % 10 + '0'; - } - } - - private: - static constexpr size_t kDigitsPerChunk = 9; - - int decimal_start_; - int decimal_end_; - - char digits_[kDigitsPerChunk]; - int size_ = 0; - - absl::Span<uint32_t> data_; -}; - -// Converts a value of the form `x * 2^-exp` into a sequence of decimal digits. -// Requires `-exp < 0` and -// `-exp >= limits<long double>::min_exponent - limits<long double>::digits`. -class FractionalDigitGenerator { - public: - // Run the conversion for `v * 2^exp` and call `f(generator)`. - // This function will allocate enough stack space to perform the conversion. - static void RunConversion( - uint128 v, int exp, absl::FunctionRef<void(FractionalDigitGenerator)> f) { - using Limits = std::numeric_limits<long double>; - assert(-exp < 0); - assert(-exp >= Limits::min_exponent - 128); - static_assert(StackArray::kMaxCapacity >= - (Limits::digits + 128 - Limits::min_exponent + 31) / 32, - ""); - StackArray::RunWithCapacity((Limits::digits + exp + 31) / 32, - [=](absl::Span<uint32_t> input) { - f(FractionalDigitGenerator(input, v, exp)); - }); - } - - // Returns true if there are any more non-zero digits left. - bool HasMoreDigits() const { return next_digit_ != 0 || chunk_index_ >= 0; } - - // Returns true if the remainder digits are greater than 5000... - bool IsGreaterThanHalf() const { - return next_digit_ > 5 || (next_digit_ == 5 && chunk_index_ >= 0); - } - // Returns true if the remainder digits are exactly 5000... - bool IsExactlyHalf() const { return next_digit_ == 5 && chunk_index_ < 0; } - - struct Digits { - int digit_before_nine; - int num_nines; - }; - - // Get the next set of digits. - // They are composed by a non-9 digit followed by a runs of zero or more 9s. - Digits GetDigits() { - Digits digits{next_digit_, 0}; - - next_digit_ = GetOneDigit(); - while (next_digit_ == 9) { - ++digits.num_nines; - next_digit_ = GetOneDigit(); - } - - return digits; - } - - private: - // Return the next digit. - int GetOneDigit() { - if (chunk_index_ < 0) return 0; - - uint32_t carry = 0; - for (int i = chunk_index_; i >= 0; --i) { - carry = MultiplyBy10WithCarry(&data_[i], carry); - } - // If the lowest chunk is now empty, remove it from view. - if (data_[chunk_index_] == 0) --chunk_index_; - return carry; - } - - FractionalDigitGenerator(absl::Span<uint32_t> data, uint128 v, int exp) - : chunk_index_(exp / 32), data_(data) { - const int offset = exp % 32; - // Right shift `v` by `exp` bits. - data_[chunk_index_] = static_cast<uint32_t>(v << (32 - offset)); - v >>= offset; - // Make sure we don't overflow the data. We already calculated that - // non-zero bits fit, so we might not have space for leading zero bits. - for (int pos = chunk_index_; v; v >>= 32) - data_[--pos] = static_cast<uint32_t>(v); - - // Fill next_digit_, as GetDigits expects it to be populated always. - next_digit_ = GetOneDigit(); - } - - int next_digit_; - int chunk_index_; - absl::Span<uint32_t> data_; -}; - -// Count the number of leading zero bits. -int LeadingZeros(uint64_t v) { return base_internal::CountLeadingZeros64(v); } -int LeadingZeros(uint128 v) { - auto high = static_cast<uint64_t>(v >> 64); - auto low = static_cast<uint64_t>(v); - return high != 0 ? base_internal::CountLeadingZeros64(high) - : 64 + base_internal::CountLeadingZeros64(low); -} - -// Round up the text digits starting at `p`. -// The buffer must have an extra digit that is known to not need rounding. -// This is done below by having an extra '0' digit on the left. -void RoundUp(char *p) { - while (*p == '9' || *p == '.') { - if (*p == '9') *p = '0'; - --p; - } - ++*p; -} - -// Check the previous digit and round up or down to follow the round-to-even -// policy. -void RoundToEven(char *p) { - if (*p == '.') --p; - if (*p % 2 == 1) RoundUp(p); -} - -// Simple integral decimal digit printing for values that fit in 64-bits. -// Returns the pointer to the last written digit. -char *PrintIntegralDigitsFromRightFast(uint64_t v, char *p) { - do { - *--p = DivideBy10WithCarry(&v, 0) + '0'; - } while (v != 0); - return p; -} - -// Simple integral decimal digit printing for values that fit in 128-bits. -// Returns the pointer to the last written digit. -char *PrintIntegralDigitsFromRightFast(uint128 v, char *p) { - auto high = static_cast<uint64_t>(v >> 64); - auto low = static_cast<uint64_t>(v); - - while (high != 0) { - uint64_t carry = DivideBy10WithCarry(&high, 0); - carry = DivideBy10WithCarry(&low, carry); - *--p = carry + '0'; - } - return PrintIntegralDigitsFromRightFast(low, p); -} - -// Simple fractional decimal digit printing for values that fir in 64-bits after -// shifting. -// Performs rounding if necessary to fit within `precision`. -// Returns the pointer to one after the last character written. -char *PrintFractionalDigitsFast(uint64_t v, char *start, int exp, - int precision) { - char *p = start; - v <<= (64 - exp); - while (precision > 0) { - if (!v) return p; - *p++ = MultiplyBy10WithCarry(&v, uint64_t{0}) + '0'; - --precision; - } - - // We need to round. - if (v < 0x8000000000000000) { - // We round down, so nothing to do. - } else if (v > 0x8000000000000000) { - // We round up. - RoundUp(p - 1); - } else { - RoundToEven(p - 1); - } - - assert(precision == 0); - // Precision can only be zero here. - return p; -} - -// Simple fractional decimal digit printing for values that fir in 128-bits -// after shifting. -// Performs rounding if necessary to fit within `precision`. -// Returns the pointer to one after the last character written. -char *PrintFractionalDigitsFast(uint128 v, char *start, int exp, - int precision) { - char *p = start; - v <<= (128 - exp); - auto high = static_cast<uint64_t>(v >> 64); - auto low = static_cast<uint64_t>(v); - - // While we have digits to print and `low` is not empty, do the long - // multiplication. - while (precision > 0 && low != 0) { - uint64_t carry = MultiplyBy10WithCarry(&low, uint64_t{0}); - carry = MultiplyBy10WithCarry(&high, carry); - - *p++ = carry + '0'; - --precision; - } - - // Now `low` is empty, so use a faster approach for the rest of the digits. - // This block is pretty much the same as the main loop for the 64-bit case - // above. - while (precision > 0) { - if (!high) return p; - *p++ = MultiplyBy10WithCarry(&high, uint64_t{0}) + '0'; - --precision; - } - - // We need to round. - if (high < 0x8000000000000000) { - // We round down, so nothing to do. - } else if (high > 0x8000000000000000 || low != 0) { - // We round up. - RoundUp(p - 1); - } else { - RoundToEven(p - 1); - } - - assert(precision == 0); - // Precision can only be zero here. - return p; -} - -struct FormatState { - char sign_char; - int precision; - const FormatConversionSpecImpl &conv; - FormatSinkImpl *sink; - - // In `alt` mode (flag #) we keep the `.` even if there are no fractional - // digits. In non-alt mode, we strip it. - bool ShouldPrintDot() const { return precision != 0 || conv.has_alt_flag(); } -}; - -struct Padding { - int left_spaces; - int zeros; - int right_spaces; -}; - -Padding ExtraWidthToPadding(size_t total_size, const FormatState &state) { - if (state.conv.width() < 0 || state.conv.width() <= total_size) - return {0, 0, 0}; - int missing_chars = state.conv.width() - total_size; - if (state.conv.has_left_flag()) { - return {0, 0, missing_chars}; - } else if (state.conv.has_zero_flag()) { - return {0, missing_chars, 0}; - } else { - return {missing_chars, 0, 0}; - } -} - -void FinalPrint(absl::string_view data, int trailing_zeros, - const FormatState &state) { - if (state.conv.width() < 0) { - // No width specified. Fast-path. - if (state.sign_char != '\0') state.sink->Append(1, state.sign_char); - state.sink->Append(data); - state.sink->Append(trailing_zeros, '0'); - return; - } - - auto padding = - ExtraWidthToPadding((state.sign_char != '\0' ? 1 : 0) + data.size() + - static_cast<size_t>(trailing_zeros), - state); - - state.sink->Append(padding.left_spaces, ' '); - if (state.sign_char != '\0') state.sink->Append(1, state.sign_char); - state.sink->Append(padding.zeros, '0'); - state.sink->Append(data); - state.sink->Append(trailing_zeros, '0'); - state.sink->Append(padding.right_spaces, ' '); -} - -// Fastpath %f formatter for when the shifted value fits in a simple integral -// type. -// Prints `v*2^exp` with the options from `state`. -template <typename Int> -void FormatFFast(Int v, int exp, const FormatState &state) { - constexpr int input_bits = sizeof(Int) * 8; - - static constexpr size_t integral_size = - /* in case we need to round up an extra digit */ 1 + - /* decimal digits for uint128 */ 40 + 1; - char buffer[integral_size + /* . */ 1 + /* max digits uint128 */ 128]; - buffer[integral_size] = '.'; - char *const integral_digits_end = buffer + integral_size; - char *integral_digits_start; - char *const fractional_digits_start = buffer + integral_size + 1; - char *fractional_digits_end = fractional_digits_start; - - if (exp >= 0) { - const int total_bits = input_bits - LeadingZeros(v) + exp; - integral_digits_start = - total_bits <= 64 - ? PrintIntegralDigitsFromRightFast(static_cast<uint64_t>(v) << exp, - integral_digits_end) - : PrintIntegralDigitsFromRightFast(static_cast<uint128>(v) << exp, - integral_digits_end); - } else { - exp = -exp; - - integral_digits_start = PrintIntegralDigitsFromRightFast( - exp < input_bits ? v >> exp : 0, integral_digits_end); - // PrintFractionalDigits may pull a carried 1 all the way up through the - // integral portion. - integral_digits_start[-1] = '0'; - - fractional_digits_end = - exp <= 64 ? PrintFractionalDigitsFast(v, fractional_digits_start, exp, - state.precision) - : PrintFractionalDigitsFast(static_cast<uint128>(v), - fractional_digits_start, exp, - state.precision); - // There was a carry, so include the first digit too. - if (integral_digits_start[-1] != '0') --integral_digits_start; - } - - size_t size = fractional_digits_end - integral_digits_start; - - // In `alt` mode (flag #) we keep the `.` even if there are no fractional - // digits. In non-alt mode, we strip it. - if (!state.ShouldPrintDot()) --size; - FinalPrint(absl::string_view(integral_digits_start, size), - static_cast<int>(state.precision - (fractional_digits_end - - fractional_digits_start)), - state); -} - -// Slow %f formatter for when the shifted value does not fit in a uint128, and -// `exp > 0`. -// Prints `v*2^exp` with the options from `state`. -// This one is guaranteed to not have fractional digits, so we don't have to -// worry about anything after the `.`. -void FormatFPositiveExpSlow(uint128 v, int exp, const FormatState &state) { - BinaryToDecimal::RunConversion(v, exp, [&](BinaryToDecimal btd) { - const size_t total_digits = - btd.TotalDigits() + - (state.ShouldPrintDot() ? static_cast<size_t>(state.precision) + 1 : 0); - - const auto padding = ExtraWidthToPadding( - total_digits + (state.sign_char != '\0' ? 1 : 0), state); - - state.sink->Append(padding.left_spaces, ' '); - if (state.sign_char != '\0') state.sink->Append(1, state.sign_char); - state.sink->Append(padding.zeros, '0'); - - do { - state.sink->Append(btd.CurrentDigits()); - } while (btd.AdvanceDigits()); - - if (state.ShouldPrintDot()) state.sink->Append(1, '.'); - state.sink->Append(state.precision, '0'); - state.sink->Append(padding.right_spaces, ' '); - }); -} - -// Slow %f formatter for when the shifted value does not fit in a uint128, and -// `exp < 0`. -// Prints `v*2^exp` with the options from `state`. -// This one is guaranteed to be < 1.0, so we don't have to worry about integral -// digits. -void FormatFNegativeExpSlow(uint128 v, int exp, const FormatState &state) { - const size_t total_digits = - /* 0 */ 1 + - (state.ShouldPrintDot() ? static_cast<size_t>(state.precision) + 1 : 0); - auto padding = - ExtraWidthToPadding(total_digits + (state.sign_char ? 1 : 0), state); - padding.zeros += 1; - state.sink->Append(padding.left_spaces, ' '); - if (state.sign_char != '\0') state.sink->Append(1, state.sign_char); - state.sink->Append(padding.zeros, '0'); - - if (state.ShouldPrintDot()) state.sink->Append(1, '.'); - - // Print digits - int digits_to_go = state.precision; - - FractionalDigitGenerator::RunConversion( - v, exp, [&](FractionalDigitGenerator digit_gen) { - // There are no digits to print here. - if (state.precision == 0) return; - - // We go one digit at a time, while keeping track of runs of nines. - // The runs of nines are used to perform rounding when necessary. - - while (digits_to_go > 0 && digit_gen.HasMoreDigits()) { - auto digits = digit_gen.GetDigits(); - - // Now we have a digit and a run of nines. - // See if we can print them all. - if (digits.num_nines + 1 < digits_to_go) { - // We don't have to round yet, so print them. - state.sink->Append(1, digits.digit_before_nine + '0'); - state.sink->Append(digits.num_nines, '9'); - digits_to_go -= digits.num_nines + 1; - - } else { - // We can't print all the nines, see where we have to truncate. - - bool round_up = false; - if (digits.num_nines + 1 > digits_to_go) { - // We round up at a nine. No need to print them. - round_up = true; - } else { - // We can fit all the nines, but truncate just after it. - if (digit_gen.IsGreaterThanHalf()) { - round_up = true; - } else if (digit_gen.IsExactlyHalf()) { - // Round to even - round_up = - digits.num_nines != 0 || digits.digit_before_nine % 2 == 1; - } - } - - if (round_up) { - state.sink->Append(1, digits.digit_before_nine + '1'); - --digits_to_go; - // The rest will be zeros. - } else { - state.sink->Append(1, digits.digit_before_nine + '0'); - state.sink->Append(digits_to_go - 1, '9'); - digits_to_go = 0; - } - return; - } - } - }); - - state.sink->Append(digits_to_go, '0'); - state.sink->Append(padding.right_spaces, ' '); -} - -template <typename Int> -void FormatF(Int mantissa, int exp, const FormatState &state) { - if (exp >= 0) { - const int total_bits = sizeof(Int) * 8 - LeadingZeros(mantissa) + exp; - - // Fallback to the slow stack-based approach if we can't do it in a 64 or - // 128 bit state. - if (ABSL_PREDICT_FALSE(total_bits > 128)) { - return FormatFPositiveExpSlow(mantissa, exp, state); - } - } else { - // Fallback to the slow stack-based approach if we can't do it in a 64 or - // 128 bit state. - if (ABSL_PREDICT_FALSE(exp < -128)) { - return FormatFNegativeExpSlow(mantissa, -exp, state); - } - } - return FormatFFast(mantissa, exp, state); -} - -char *CopyStringTo(absl::string_view v, char *out) { - std::memcpy(out, v.data(), v.size()); - return out + v.size(); -} - -template <typename Float> -bool FallbackToSnprintf(const Float v, const FormatConversionSpecImpl &conv, - FormatSinkImpl *sink) { - int w = conv.width() >= 0 ? conv.width() : 0; - int p = conv.precision() >= 0 ? conv.precision() : -1; - char fmt[32]; - { - char *fp = fmt; - *fp++ = '%'; - fp = CopyStringTo(FormatConversionSpecImplFriend::FlagsToString(conv), fp); - fp = CopyStringTo("*.*", fp); - if (std::is_same<long double, Float>()) { - *fp++ = 'L'; - } - *fp++ = FormatConversionCharToChar(conv.conversion_char()); - *fp = 0; - assert(fp < fmt + sizeof(fmt)); - } - std::string space(512, '\0'); - absl::string_view result; - while (true) { - int n = snprintf(&space[0], space.size(), fmt, w, p, v); - if (n < 0) return false; - if (static_cast<size_t>(n) < space.size()) { - result = absl::string_view(space.data(), n); - break; - } - space.resize(n + 1); - } - sink->Append(result); - return true; -} - -// 128-bits in decimal: ceil(128*log(2)/log(10)) -// or std::numeric_limits<__uint128_t>::digits10 -constexpr int kMaxFixedPrecision = 39; - -constexpr int kBufferLength = /*sign*/ 1 + - /*integer*/ kMaxFixedPrecision + - /*point*/ 1 + - /*fraction*/ kMaxFixedPrecision + - /*exponent e+123*/ 5; - -struct Buffer { - void push_front(char c) { - assert(begin > data); - *--begin = c; - } - void push_back(char c) { - assert(end < data + sizeof(data)); - *end++ = c; - } - void pop_back() { - assert(begin < end); - --end; - } - - char &back() { - assert(begin < end); - return end[-1]; - } - - char last_digit() const { return end[-1] == '.' ? end[-2] : end[-1]; } - - int size() const { return static_cast<int>(end - begin); } - - char data[kBufferLength]; - char *begin; - char *end; -}; - -enum class FormatStyle { Fixed, Precision }; - -// If the value is Inf or Nan, print it and return true. -// Otherwise, return false. -template <typename Float> -bool ConvertNonNumericFloats(char sign_char, Float v, - const FormatConversionSpecImpl &conv, - FormatSinkImpl *sink) { - char text[4], *ptr = text; - if (sign_char != '\0') *ptr++ = sign_char; - if (std::isnan(v)) { - ptr = std::copy_n( - FormatConversionCharIsUpper(conv.conversion_char()) ? "NAN" : "nan", 3, - ptr); - } else if (std::isinf(v)) { - ptr = std::copy_n( - FormatConversionCharIsUpper(conv.conversion_char()) ? "INF" : "inf", 3, - ptr); - } else { - return false; - } - - return sink->PutPaddedString(string_view(text, ptr - text), conv.width(), -1, - conv.has_left_flag()); -} - -// Round up the last digit of the value. -// It will carry over and potentially overflow. 'exp' will be adjusted in that -// case. -template <FormatStyle mode> -void RoundUp(Buffer *buffer, int *exp) { - char *p = &buffer->back(); - while (p >= buffer->begin && (*p == '9' || *p == '.')) { - if (*p == '9') *p = '0'; - --p; - } - - if (p < buffer->begin) { - *p = '1'; - buffer->begin = p; - if (mode == FormatStyle::Precision) { - std::swap(p[1], p[2]); // move the . - ++*exp; - buffer->pop_back(); - } - } else { - ++*p; - } -} - -void PrintExponent(int exp, char e, Buffer *out) { - out->push_back(e); - if (exp < 0) { - out->push_back('-'); - exp = -exp; - } else { - out->push_back('+'); - } - // Exponent digits. - if (exp > 99) { - out->push_back(exp / 100 + '0'); - out->push_back(exp / 10 % 10 + '0'); - out->push_back(exp % 10 + '0'); - } else { - out->push_back(exp / 10 + '0'); - out->push_back(exp % 10 + '0'); - } -} - -template <typename Float, typename Int> -constexpr bool CanFitMantissa() { - return -#if defined(__clang__) && !defined(__SSE3__) - // Workaround for clang bug: https://bugs.llvm.org/show_bug.cgi?id=38289 - // Casting from long double to uint64_t is miscompiled and drops bits. - (!std::is_same<Float, long double>::value || - !std::is_same<Int, uint64_t>::value) && -#endif - std::numeric_limits<Float>::digits <= std::numeric_limits<Int>::digits; -} - -template <typename Float> -struct Decomposed { - using MantissaType = - absl::conditional_t<std::is_same<long double, Float>::value, uint128, - uint64_t>; - static_assert(std::numeric_limits<Float>::digits <= sizeof(MantissaType) * 8, - ""); - MantissaType mantissa; - int exponent; -}; - -// Decompose the double into an integer mantissa and an exponent. -template <typename Float> -Decomposed<Float> Decompose(Float v) { - int exp; - Float m = std::frexp(v, &exp); - m = std::ldexp(m, std::numeric_limits<Float>::digits); - exp -= std::numeric_limits<Float>::digits; - - return {static_cast<typename Decomposed<Float>::MantissaType>(m), exp}; -} - -// Print 'digits' as decimal. -// In Fixed mode, we add a '.' at the end. -// In Precision mode, we add a '.' after the first digit. -template <FormatStyle mode, typename Int> -int PrintIntegralDigits(Int digits, Buffer *out) { - int printed = 0; - if (digits) { - for (; digits; digits /= 10) out->push_front(digits % 10 + '0'); - printed = out->size(); - if (mode == FormatStyle::Precision) { - out->push_front(*out->begin); - out->begin[1] = '.'; - } else { - out->push_back('.'); - } - } else if (mode == FormatStyle::Fixed) { - out->push_front('0'); - out->push_back('.'); - printed = 1; - } - return printed; -} - -// Back out 'extra_digits' digits and round up if necessary. -bool RemoveExtraPrecision(int extra_digits, bool has_leftover_value, - Buffer *out, int *exp_out) { - if (extra_digits <= 0) return false; - - // Back out the extra digits - out->end -= extra_digits; - - bool needs_to_round_up = [&] { - // We look at the digit just past the end. - // There must be 'extra_digits' extra valid digits after end. - if (*out->end > '5') return true; - if (*out->end < '5') return false; - if (has_leftover_value || std::any_of(out->end + 1, out->end + extra_digits, - [](char c) { return c != '0'; })) - return true; - - // Ends in ...50*, round to even. - return out->last_digit() % 2 == 1; - }(); - - if (needs_to_round_up) { - RoundUp<FormatStyle::Precision>(out, exp_out); - } - return true; -} - -// Print the value into the buffer. -// This will not include the exponent, which will be returned in 'exp_out' for -// Precision mode. -template <typename Int, typename Float, FormatStyle mode> -bool FloatToBufferImpl(Int int_mantissa, int exp, int precision, Buffer *out, - int *exp_out) { - assert((CanFitMantissa<Float, Int>())); - - const int int_bits = std::numeric_limits<Int>::digits; - - // In precision mode, we start printing one char to the right because it will - // also include the '.' - // In fixed mode we put the dot afterwards on the right. - out->begin = out->end = - out->data + 1 + kMaxFixedPrecision + (mode == FormatStyle::Precision); - - if (exp >= 0) { - if (std::numeric_limits<Float>::digits + exp > int_bits) { - // The value will overflow the Int - return false; - } - int digits_printed = PrintIntegralDigits<mode>(int_mantissa << exp, out); - int digits_to_zero_pad = precision; - if (mode == FormatStyle::Precision) { - *exp_out = digits_printed - 1; - digits_to_zero_pad -= digits_printed - 1; - if (RemoveExtraPrecision(-digits_to_zero_pad, false, out, exp_out)) { - return true; - } - } - for (; digits_to_zero_pad-- > 0;) out->push_back('0'); - return true; - } - - exp = -exp; - // We need at least 4 empty bits for the next decimal digit. - // We will multiply by 10. - if (exp > int_bits - 4) return false; - - const Int mask = (Int{1} << exp) - 1; - - // Print the integral part first. - int digits_printed = PrintIntegralDigits<mode>(int_mantissa >> exp, out); - int_mantissa &= mask; - - int fractional_count = precision; - if (mode == FormatStyle::Precision) { - if (digits_printed == 0) { - // Find the first non-zero digit, when in Precision mode. - *exp_out = 0; - if (int_mantissa) { - while (int_mantissa <= mask) { - int_mantissa *= 10; - --*exp_out; - } - } - out->push_front(static_cast<char>(int_mantissa >> exp) + '0'); - out->push_back('.'); - int_mantissa &= mask; - } else { - // We already have a digit, and a '.' - *exp_out = digits_printed - 1; - fractional_count -= *exp_out; - if (RemoveExtraPrecision(-fractional_count, int_mantissa != 0, out, - exp_out)) { - // If we had enough digits, return right away. - // The code below will try to round again otherwise. - return true; - } - } - } - - auto get_next_digit = [&] { - int_mantissa *= 10; - int digit = static_cast<int>(int_mantissa >> exp); - int_mantissa &= mask; - return digit; - }; - - // Print fractional_count more digits, if available. - for (; fractional_count > 0; --fractional_count) { - out->push_back(get_next_digit() + '0'); - } - - int next_digit = get_next_digit(); - if (next_digit > 5 || - (next_digit == 5 && (int_mantissa || out->last_digit() % 2 == 1))) { - RoundUp<mode>(out, exp_out); - } - - return true; -} - -template <FormatStyle mode, typename Float> -bool FloatToBuffer(Decomposed<Float> decomposed, int precision, Buffer *out, - int *exp) { - if (precision > kMaxFixedPrecision) return false; - - // Try with uint64_t. - if (CanFitMantissa<Float, std::uint64_t>() && - FloatToBufferImpl<std::uint64_t, Float, mode>( - static_cast<std::uint64_t>(decomposed.mantissa), - static_cast<std::uint64_t>(decomposed.exponent), precision, out, exp)) - return true; - -#if defined(ABSL_HAVE_INTRINSIC_INT128) - // If that is not enough, try with __uint128_t. - return CanFitMantissa<Float, __uint128_t>() && - FloatToBufferImpl<__uint128_t, Float, mode>( - static_cast<__uint128_t>(decomposed.mantissa), - static_cast<__uint128_t>(decomposed.exponent), precision, out, - exp); -#endif - return false; -} - -void WriteBufferToSink(char sign_char, absl::string_view str, - const FormatConversionSpecImpl &conv, - FormatSinkImpl *sink) { - int left_spaces = 0, zeros = 0, right_spaces = 0; - int missing_chars = - conv.width() >= 0 ? std::max(conv.width() - static_cast<int>(str.size()) - - static_cast<int>(sign_char != 0), - 0) - : 0; - if (conv.has_left_flag()) { - right_spaces = missing_chars; - } else if (conv.has_zero_flag()) { - zeros = missing_chars; - } else { - left_spaces = missing_chars; - } - - sink->Append(left_spaces, ' '); - if (sign_char != '\0') sink->Append(1, sign_char); - sink->Append(zeros, '0'); - sink->Append(str); - sink->Append(right_spaces, ' '); -} - -template <typename Float> -bool FloatToSink(const Float v, const FormatConversionSpecImpl &conv, - FormatSinkImpl *sink) { - // Print the sign or the sign column. - Float abs_v = v; - char sign_char = 0; - if (std::signbit(abs_v)) { - sign_char = '-'; - abs_v = -abs_v; - } else if (conv.has_show_pos_flag()) { - sign_char = '+'; - } else if (conv.has_sign_col_flag()) { - sign_char = ' '; - } - - // Print nan/inf. - if (ConvertNonNumericFloats(sign_char, abs_v, conv, sink)) { - return true; - } - - int precision = conv.precision() < 0 ? 6 : conv.precision(); - - int exp = 0; - - auto decomposed = Decompose(abs_v); - - Buffer buffer; - - FormatConversionChar c = conv.conversion_char(); - - if (c == FormatConversionCharInternal::f || - c == FormatConversionCharInternal::F) { - FormatF(decomposed.mantissa, decomposed.exponent, - {sign_char, precision, conv, sink}); - return true; - } else if (c == FormatConversionCharInternal::e || - c == FormatConversionCharInternal::E) { - if (!FloatToBuffer<FormatStyle::Precision>(decomposed, precision, &buffer, - &exp)) { - return FallbackToSnprintf(v, conv, sink); - } - if (!conv.has_alt_flag() && buffer.back() == '.') buffer.pop_back(); - PrintExponent( - exp, FormatConversionCharIsUpper(conv.conversion_char()) ? 'E' : 'e', - &buffer); - } else if (c == FormatConversionCharInternal::g || - c == FormatConversionCharInternal::G) { - precision = std::max(0, precision - 1); - if (!FloatToBuffer<FormatStyle::Precision>(decomposed, precision, &buffer, - &exp)) { - return FallbackToSnprintf(v, conv, sink); - } - if (precision + 1 > exp && exp >= -4) { - if (exp < 0) { - // Have 1.23456, needs 0.00123456 - // Move the first digit - buffer.begin[1] = *buffer.begin; - // Add some zeros - for (; exp < -1; ++exp) *buffer.begin-- = '0'; - *buffer.begin-- = '.'; - *buffer.begin = '0'; - } else if (exp > 0) { - // Have 1.23456, needs 1234.56 - // Move the '.' exp positions to the right. - std::rotate(buffer.begin + 1, buffer.begin + 2, buffer.begin + exp + 2); - } - exp = 0; - } - if (!conv.has_alt_flag()) { - while (buffer.back() == '0') buffer.pop_back(); - if (buffer.back() == '.') buffer.pop_back(); - } - if (exp) { - PrintExponent( - exp, FormatConversionCharIsUpper(conv.conversion_char()) ? 'E' : 'e', - &buffer); - } - } else if (c == FormatConversionCharInternal::a || - c == FormatConversionCharInternal::A) { - return FallbackToSnprintf(v, conv, sink); - } else { - return false; - } - - WriteBufferToSink(sign_char, - absl::string_view(buffer.begin, buffer.end - buffer.begin), - conv, sink); - - return true; -} - -} // namespace - -bool ConvertFloatImpl(long double v, const FormatConversionSpecImpl &conv, - FormatSinkImpl *sink) { - if (std::numeric_limits<long double>::digits == - 2 * std::numeric_limits<double>::digits) { - // This is the `double-double` representation of `long double`. - // We do not handle it natively. Fallback to snprintf. - return FallbackToSnprintf(v, conv, sink); - } - - return FloatToSink(v, conv, sink); -} - -bool ConvertFloatImpl(float v, const FormatConversionSpecImpl &conv, - FormatSinkImpl *sink) { - return FloatToSink(v, conv, sink); -} - -bool ConvertFloatImpl(double v, const FormatConversionSpecImpl &conv, - FormatSinkImpl *sink) { - return FloatToSink(v, conv, sink); -} - -} // namespace str_format_internal -ABSL_NAMESPACE_END -} // namespace absl |