diff options
Diffstat (limited to 'absl/strings/internal/str_format/float_conversion.cc')
| -rw-r--r-- | absl/strings/internal/str_format/float_conversion.cc | 497 |
1 files changed, 11 insertions, 486 deletions
diff --git a/absl/strings/internal/str_format/float_conversion.cc b/absl/strings/internal/str_format/float_conversion.cc index 20012b5876cc..6176db9cb5a2 100644 --- a/absl/strings/internal/str_format/float_conversion.cc +++ b/absl/strings/internal/str_format/float_conversion.cc @@ -2,476 +2,15 @@ #include <string.h> #include <algorithm> -#include <array> #include <cassert> #include <cmath> -#include <limits> #include <string> -#include "absl/base/attributes.h" -#include "absl/base/internal/bits.h" -#include "absl/base/optimization.h" -#include "absl/meta/type_traits.h" -#include "absl/numeric/int128.h" -#include "absl/types/span.h" - namespace absl { namespace str_format_internal { namespace { -// 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 NextInt = absl::conditional_t<sizeof(Int) == 4, uint64_t, uint128>; - static_assert(sizeof(void *) >= sizeof(Int), - "Don't want to use uint128 in 32-bit mode. It is too slow."); - NextInt tmp = 10 * static_cast<NextInt>(*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 = word_quotient + word_remainder / divisor - constexpr uint64_t word_quotient = (uint64_t{1} << 63) / (divisor / 2); - constexpr uint64_t word_remainder = uint64_t{} - word_quotient * divisor; - - const uint64_t mod = *v % divisor; - const uint64_t next_carry = word_remainder * carry + mod; - *v = *v / divisor + carry * word_quotient + next_carry / divisor; - return next_carry % divisor; -} - -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); -} - -int TrailingZeros(uint64_t v) { - return base_internal::CountTrailingZerosNonZero64(v); -} -int TrailingZeros(uint128 v) { - auto high = static_cast<uint64_t>(v >> 64); - auto low = static_cast<uint64_t>(v); - return low == 0 ? 64 + base_internal::CountTrailingZerosNonZero64(high) - : base_internal::CountTrailingZerosNonZero64(low); -} - -// 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 *last_digit) { - char *p = last_digit; - while (*p == '9' || *p == '.') { - if (*p == '9') *p = '0'; - --p; - } - ++*p; -} - -void RoundToEven(char *last_digit) { - char *p = last_digit; - if (*p == '.') --p; - if (*p % 2 == 1) RoundUp(p); -} - -char *PrintIntegralDigitsFromRightDynamic(uint128 v, Span<uint32_t> array, - int exp, char *p) { - if (v == 0) { - *--p = '0'; - return p; - } - - int w = exp / 32; - const int offset = exp % 32; - // Left shift v by exp bits. - array[w] = static_cast<uint32_t>(v << offset); - for (v >>= (32 - offset); v; v >>= 32) array[++w] = static_cast<uint32_t>(v); - - // While we have more than one word available, go in chunks of 1e9. - // We are guaranteed to have at least those many digits. - // `w` holds the largest populated word, so keep it updated. - while (w > 0) { - uint32_t carry = 0; - for (int i = w; i >= 0; --i) { - uint64_t tmp = uint64_t{array[i]} + (uint64_t{carry} << 32); - array[i] = tmp / uint64_t{1000000000}; - carry = tmp % uint64_t{1000000000}; - } - // If the highest word is now empty, remove it from view. - if (array[w] == 0) --w; - - for (int i = 0; i < 9; ++i, carry /= 10) { - *--p = carry % 10 + '0'; - } - } - - // Print the leftover of the last word. - for (auto last = array[0]; last != 0; last /= 10) { - *--p = last % 10 + '0'; - } - - return p; -} - -struct FractionalResult { - const char *end; - int precision; -}; - -FractionalResult PrintFractionalDigitsDynamic(uint128 v, Span<uint32_t> array, - char *p, int exp, int precision) { - int w = exp / 32; - const int offset = exp % 32; - - // Right shift `v` by `exp` bits. - array[w] = static_cast<uint32_t>(v << (32 - offset)); - v >>= offset; - // Make sure we don't overflow the array. We already calculated that non-zero - // bits fit, so we might not have space for leading zero bits. - for (int pos = w; v; v >>= 32) array[--pos] = static_cast<uint32_t>(v); - - // Multiply the whole sequence by 10. - // On each iteration, the leftover carry word is the next digit. - // `w` holds the largest populated word, so keep it updated. - for (; w >= 0 && precision > 0; --precision) { - uint32_t carry = 0; - for (int i = w; i >= 0; --i) { - carry = MultiplyBy10WithCarry(&array[i], carry); - } - // If the lowest word is now empty, remove it from view. - if (array[w] == 0) --w; - *p++ = carry + '0'; - } - - constexpr uint32_t threshold = 0x80000000; - if (array[0] < threshold) { - // We round down, so nothing to do. - } else if (array[0] > threshold || - std::any_of(&array[1], &array[w + 1], - [](uint32_t word) { return word != 0; })) { - RoundUp(p - 1); - } else { - RoundToEven(p - 1); - } - return {p, precision}; -} - -// Generic digit printer. -// `bits` determines how many bits of termporary space it needs for the -// calcualtions. -template <int bits, typename = void> -class DigitPrinter { - static constexpr int kInts = (bits + 31) / 32; - - public: - // Quick upper bound for the number of decimal digits we need. - // This would be std::ceil(std::log10(std::pow(2, bits))), but that is not - // constexpr. - static constexpr int kDigits10 = 1 + (bits + 9) / 10 * 3 + bits / 900; - using InputType = uint128; - - static char *PrintIntegralDigitsFromRight(InputType v, int exp, char *end) { - std::array<uint32_t, kInts> array{}; - return PrintIntegralDigitsFromRightDynamic(v, absl::MakeSpan(array), exp, - end); - } - - static FractionalResult PrintFractionalDigits(InputType v, char *p, int exp, - int precision) { - std::array<uint32_t, kInts> array{}; - return PrintFractionalDigitsDynamic(v, absl::MakeSpan(array), p, exp, - precision); - } -}; - -// Specialiation for 64-bit working space. -// This is a performance optimization over the generic primary template. -// Only enabled in 64-bit platforms. The generic one is faster in 32-bit -// platforms. -template <int bits> -class DigitPrinter<bits, absl::enable_if_t<bits == 64 && (sizeof(void *) >= - sizeof(uint64_t))>> { - public: - static constexpr size_t kDigits10 = 20; - using InputType = uint64_t; - - static char *PrintIntegralDigitsFromRight(uint64_t v, int exp, char *p) { - v <<= exp; - do { - *--p = DivideBy10WithCarry(&v, 0) + '0'; - } while (v != 0); - return p; - } - - static FractionalResult PrintFractionalDigits(uint64_t v, char *p, int exp, - int precision) { - v <<= (64 - exp); - while (precision > 0) { - if (!v) return {p, precision}; - *p++ = MultiplyBy10WithCarry(&v, uint64_t{}) + '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 a constant instead. - return {p, 0}; - } -}; - -// Specialiation for 128-bit working space. -// This is a performance optimization over the generic primary template. -template <int bits> -class DigitPrinter<bits, absl::enable_if_t<bits == 128 && (sizeof(void *) >= - sizeof(uint64_t))>> { - public: - static constexpr size_t kDigits10 = 40; - using InputType = uint128; - - static char *PrintIntegralDigitsFromRight(uint128 v, int exp, char *p) { - v <<= exp; - auto high = static_cast<uint64_t>(v >> 64); - auto low = static_cast<uint64_t>(v); - - do { - uint64_t carry = DivideBy10WithCarry(&high, 0); - carry = DivideBy10WithCarry(&low, carry); - *--p = carry + '0'; - } while (high != 0u); - - while (low != 0u) { - *--p = DivideBy10WithCarry(&low, 0) + '0'; - } - return p; - } - - static FractionalResult PrintFractionalDigits(uint128 v, char *p, int exp, - int precision) { - 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{}); - 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, precision}; - *p++ = MultiplyBy10WithCarry(&high, uint64_t{}) + '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 a constant instead. - return {p, 0}; - } -}; - -struct FormatState { - char sign_char; - int precision; - const ConversionSpec &conv; - FormatSinkImpl *sink; -}; - -void FinalPrint(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; - } - - int left_spaces = 0, zeros = 0, right_spaces = 0; - int total_size = (state.sign_char != 0 ? 1 : 0) + - static_cast<int>(data.size()) + trailing_zeros; - int missing_chars = std::max(state.conv.width() - total_size, 0); - if (state.conv.flags().left) { - right_spaces = missing_chars; - } else if (state.conv.flags().zero) { - zeros = missing_chars; - } else { - left_spaces = missing_chars; - } - - state.sink->Append(left_spaces, ' '); - if (state.sign_char != '\0') state.sink->Append(1, state.sign_char); - state.sink->Append(zeros, '0'); - state.sink->Append(data); - state.sink->Append(trailing_zeros, '0'); - state.sink->Append(right_spaces, ' '); -} - -template <int num_bits, typename Int> -void FormatFPositiveExp(Int v, int exp, const FormatState &state) { - using IntegralPrinter = DigitPrinter<num_bits>; - char buffer[IntegralPrinter::kDigits10 + /* . */ 1]; - buffer[IntegralPrinter::kDigits10] = '.'; - - const char *digits = IntegralPrinter::PrintIntegralDigitsFromRight( - static_cast<typename IntegralPrinter::InputType>(v), exp, - buffer + sizeof(buffer) - 1); - size_t size = buffer + sizeof(buffer) - digits; - - // In `alt` mode (flag #) we keep the `.` even if there are no fractional - // digits. In non-alt mode, we strip it. - if (ABSL_PREDICT_FALSE(state.precision == 0 && !state.conv.flags().alt)) { - --size; - } - - FinalPrint(string_view(digits, size), state.precision, state); -} - -template <int num_bits, typename Int> -void FormatFNegativeExp(Int v, int exp, const FormatState &state) { - constexpr int input_bits = sizeof(Int) * 8; - - using IntegralPrinter = DigitPrinter<input_bits>; - using FractionalPrinter = DigitPrinter<num_bits>; - - static constexpr size_t integral_size = - 1 + /* in case we need to round up an extra digit */ - IntegralPrinter::kDigits10 + 1; - char buffer[integral_size + /* . */ 1 + num_bits]; - buffer[integral_size] = '.'; - char *const integral_digits_end = buffer + integral_size; - char *integral_digits_start; - char *const fractional_digits_start = buffer + integral_size + 1; - - if (exp < input_bits) { - integral_digits_start = IntegralPrinter::PrintIntegralDigitsFromRight( - v >> exp, 0, integral_digits_end); - } else { - integral_digits_start = integral_digits_end - 1; - *integral_digits_start = '0'; - } - - // PrintFractionalDigits may pull a carried 1 all the way up through the - // integral portion. - integral_digits_start[-1] = '0'; - auto fractional_result = FractionalPrinter::PrintFractionalDigits( - static_cast<typename FractionalPrinter::InputType>(v), - fractional_digits_start, exp, state.precision); - if (integral_digits_start[-1] != '0') --integral_digits_start; - - size_t size = fractional_result.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 (ABSL_PREDICT_FALSE(state.precision == 0 && !state.conv.flags().alt)) { - --size; - } - FinalPrint(string_view(integral_digits_start, size), - fractional_result.precision, state); -} - -template <typename Int> -void FormatF(Int mantissa, int exp, const FormatState &state) { - // Remove trailing zeros as they are not useful. - // This helps use faster implementations/less stack space in some cases. - if (mantissa != 0) { - int trailing = TrailingZeros(mantissa); - mantissa >>= trailing; - exp += trailing; - } - - // The table driven dispatch gives us two benefits: fast distpatch and - // prevent inlining. - // We must not inline any of the functions below (other than the ones for - // 64-bit) to avoid blowing up this stack frame. - - if (exp >= 0) { - // We will left shift the mantissa. Calculate how many bits we need. - // Special case 64-bit as we will use a uint64_t for it. Use a table for the - // rest and unconditionally use uint128. - const int total_bits = sizeof(Int) * 8 - LeadingZeros(mantissa) + exp; - - if (total_bits <= 64) { - return FormatFPositiveExp<64>(mantissa, exp, state); - } else { - using Formatter = void (*)(uint128, int, const FormatState &); - static constexpr Formatter kFormatters[] = { - FormatFPositiveExp<1 << 7>, FormatFPositiveExp<1 << 8>, - FormatFPositiveExp<1 << 9>, FormatFPositiveExp<1 << 10>, - FormatFPositiveExp<1 << 11>, FormatFPositiveExp<1 << 12>, - FormatFPositiveExp<1 << 13>, FormatFPositiveExp<1 << 14>, - FormatFPositiveExp<1 << 15>, - }; - static constexpr int max_total_bits = - sizeof(Int) * 8 + std::numeric_limits<long double>::max_exponent; - assert(total_bits <= max_total_bits); - static_assert(max_total_bits <= (1 << 15), ""); - const int log2 = - 64 - LeadingZeros((static_cast<uint64_t>(total_bits) - 1) / 128); - assert(log2 < std::end(kFormatters) - std::begin(kFormatters)); - kFormatters[log2](mantissa, exp, state); - } - } else { - exp = -exp; - - // We know we don't need more than Int itself for the integral part. - // We need `precision` fractional digits, but there are at most `exp` - // non-zero digits after the decimal point. The rest will be zeros. - // Special case 64-bit as we will use a uint64_t for it. Use a table for the - // rest and unconditionally use uint128. - - if (exp <= 64) { - return FormatFNegativeExp<64>(mantissa, exp, state); - } else { - using Formatter = void (*)(uint128, int, const FormatState &); - static constexpr Formatter kFormatters[] = { - FormatFNegativeExp<1 << 7>, FormatFNegativeExp<1 << 8>, - FormatFNegativeExp<1 << 9>, FormatFNegativeExp<1 << 10>, - FormatFNegativeExp<1 << 11>, FormatFNegativeExp<1 << 12>, - FormatFNegativeExp<1 << 13>, FormatFNegativeExp<1 << 14>}; - static_assert( - -std::numeric_limits<long double>::min_exponent <= (1 << 14), ""); - const int log2 = - 64 - LeadingZeros((static_cast<uint64_t>(exp) - 1) / 128); - assert(log2 < std::end(kFormatters) - std::begin(kFormatters)); - kFormatters[log2](mantissa, exp, state); - } - } -} - char *CopyStringTo(string_view v, char *out) { std::memcpy(out, v.data(), v.size()); return out + v.size(); @@ -556,7 +95,7 @@ template <typename Float> bool ConvertNonNumericFloats(char sign_char, Float v, const ConversionSpec &conv, FormatSinkImpl *sink) { char text[4], *ptr = text; - if (sign_char != '\0') *ptr++ = sign_char; + if (sign_char) *ptr++ = sign_char; if (std::isnan(v)) { ptr = std::copy_n(conv.conv().upper() ? "NAN" : "nan", 3, ptr); } else if (std::isinf(v)) { @@ -626,12 +165,7 @@ constexpr bool CanFitMantissa() { 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; + Float mantissa; int exponent; }; @@ -642,8 +176,7 @@ Decomposed<Float> Decompose(Float v) { 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}; + return {m, exp}; } // Print 'digits' as decimal. @@ -801,7 +334,7 @@ bool FloatToBuffer(Decomposed<Float> decomposed, int precision, Buffer *out, static_cast<std::uint64_t>(decomposed.exponent), precision, out, exp)) return true; -#if defined(ABSL_HAVE_INTRINSIC_INT128) +#if defined(__SIZEOF_INT128__) // If that is not enough, try with __uint128_t. return CanFitMantissa<Float, __uint128_t>() && FloatToBufferImpl<__uint128_t, Float, mode>( @@ -829,7 +362,7 @@ void WriteBufferToSink(char sign_char, string_view str, } sink->Append(left_spaces, ' '); - if (sign_char != '\0') sink->Append(1, sign_char); + if (sign_char) sink->Append(1, sign_char); sink->Append(zeros, '0'); sink->Append(str); sink->Append(right_spaces, ' '); @@ -866,9 +399,12 @@ bool FloatToSink(const Float v, const ConversionSpec &conv, switch (conv.conv().id()) { case ConversionChar::f: case ConversionChar::F: - FormatF(decomposed.mantissa, decomposed.exponent, - {sign_char, precision, conv, sink}); - return true; + if (!FloatToBuffer<FormatStyle::Fixed>(decomposed, precision, &buffer, + nullptr)) { + return FallbackToSnprintf(v, conv, sink); + } + if (!conv.flags().alt && buffer.back() == '.') buffer.pop_back(); + break; case ConversionChar::e: case ConversionChar::E: @@ -930,22 +466,11 @@ bool FloatToSink(const Float v, const ConversionSpec &conv, bool ConvertFloatImpl(long double v, const ConversionSpec &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 ConversionSpec &conv, FormatSinkImpl *sink) { - // DivideBy10WithCarry is not actually used in some builds. This here silences - // the "unused" warning. We just need to put it in any function that is really - // used. - (void)&DivideBy10WithCarry; return FloatToSink(v, conv, sink); } |