zhjwpku commented on code in PR #182: URL: https://github.com/apache/iceberg-cpp/pull/182#discussion_r2352253498
########## src/iceberg/util/decimal.cc: ########## @@ -0,0 +1,585 @@ +/* + * Licensed to the Apache Software Foundation (ASF) under one + * or more contributor license agreements. See the NOTICE file + * distributed with this work for additional information + * regarding copyright ownership. The ASF licenses this file + * to you under the Apache License, Version 2.0 (the + * "License"); you may not use this file except in compliance + * with the License. You may obtain a copy of the License at + * + * http://www.apache.org/licenses/LICENSE-2.0 + * + * Unless required by applicable law or agreed to in writing, + * software distributed under the License is distributed on an + * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY + * KIND, either express or implied. See the License for the + * specific language governing permissions and limitations + * under the License. + */ + +/// \file iceberg/util/decimal.cc +/// \brief 128-bit fixed-point decimal numbers. +/// Adapted from Apache Arrow with only Decimal128 support. +/// https://github.com/apache/arrow/blob/main/cpp/src/arrow/util/decimal.cc + +#include "iceberg/util/decimal.h" + +#include <bit> +#include <charconv> +#include <climits> +#include <cmath> +#include <cstring> +#include <format> +#include <iomanip> +#include <limits> +#include <sstream> +#include <utility> + +#include "iceberg/exception.h" +#include "iceberg/result.h" +#include "iceberg/util/int128.h" +#include "iceberg/util/macros.h" + +namespace iceberg { + +namespace { + +struct DecimalComponents { + std::string_view while_digits; + std::string_view fractional_digits; + int32_t exponent{0}; + char sign{0}; + bool has_exponent{false}; +}; + +inline bool IsSign(char c) { return c == '+' || c == '-'; } + +inline bool IsDigit(char c) { return c >= '0' && c <= '9'; } + +inline bool IsDot(char c) { return c == '.'; } + +inline bool StartsExponent(char c) { return c == 'e' || c == 'E'; } + +inline size_t ParseDigitsRun(std::string_view str, size_t pos, std::string_view* out) { + size_t start = pos; + while (pos < str.size() && IsDigit(str[pos])) { + ++pos; + } + *out = str.substr(start, pos - start); + return pos; +} + +bool ParseDecimalComponents(std::string_view str, DecimalComponents* out) { + size_t pos = 0; + + if (str.empty()) { + return false; + } + + // Sign of the number + if (IsSign(str[pos])) { + out->sign = str[pos++]; + } + // First run of digits + pos = ParseDigitsRun(str, pos, &out->while_digits); + if (pos == str.size()) { + return !out->while_digits.empty(); + } + + // Optional dot + if (IsDot(str[pos])) { + // Second run of digits after the dot + pos = ParseDigitsRun(str, ++pos, &out->fractional_digits); + } + if (out->fractional_digits.empty() && out->while_digits.empty()) { + // Need at least some digits (whole or fractional) + return false; + } + if (pos == str.size()) { + return true; + } + + // Optional exponent part + if (StartsExponent(str[pos])) { + ++pos; + // Skip '+' sign, '-' sign will be handled by from_chars + if (pos < str.size() && str[pos] == '+') { + ++pos; + } + out->has_exponent = true; + auto [ptr, ec] = + std::from_chars(str.data() + pos, str.data() + str.size(), out->exponent); + if (ec != std::errc()) { + return false; // Failed to parse exponent + } + pos = ptr - str.data(); + } + + return pos == str.size(); +} + +constexpr auto kInt64DecimalDigits = + static_cast<size_t>(std::numeric_limits<int64_t>::digits10); + +constexpr std::array<uint64_t, kInt64DecimalDigits + 1> kUInt64PowersOfTen = { + // clang-format off + 1ULL, + 10ULL, + 100ULL, + 1000ULL, + 10000ULL, + 100000ULL, + 1000000ULL, + 10000000ULL, + 100000000ULL, + 1000000000ULL, + 10000000000ULL, + 100000000000ULL, + 1000000000000ULL, + 10000000000000ULL, + 100000000000000ULL, + 1000000000000000ULL, + 10000000000000000ULL, + 100000000000000000ULL, + 1000000000000000000ULL + // clang-format on +}; + +/// \brief Powers of ten for Decimal with scale from 0 to 38. +constexpr std::array<Decimal, Decimal::kMaxScale + 1> kDecimal128PowersOfTen = { + Decimal(1LL), + Decimal(10LL), + Decimal(100LL), + Decimal(1000LL), + Decimal(10000LL), + Decimal(100000LL), + Decimal(1000000LL), + Decimal(10000000LL), + Decimal(100000000LL), + Decimal(1000000000LL), + Decimal(10000000000LL), + Decimal(100000000000LL), + Decimal(1000000000000LL), + Decimal(10000000000000LL), + Decimal(100000000000000LL), + Decimal(1000000000000000LL), + Decimal(10000000000000000LL), + Decimal(100000000000000000LL), + Decimal(1000000000000000000LL), + Decimal(0LL, 10000000000000000000ULL), + Decimal(5LL, 7766279631452241920ULL), + Decimal(54LL, 3875820019684212736ULL), + Decimal(542LL, 1864712049423024128ULL), + Decimal(5421LL, 200376420520689664ULL), + Decimal(54210LL, 2003764205206896640ULL), + Decimal(542101LL, 1590897978359414784ULL), + Decimal(5421010LL, 15908979783594147840ULL), + Decimal(54210108LL, 11515845246265065472ULL), + Decimal(542101086LL, 4477988020393345024ULL), + Decimal(5421010862LL, 7886392056514347008ULL), + Decimal(54210108624LL, 5076944270305263616ULL), + Decimal(542101086242LL, 13875954555633532928ULL), + Decimal(5421010862427LL, 9632337040368467968ULL), + Decimal(54210108624275LL, 4089650035136921600ULL), + Decimal(542101086242752LL, 4003012203950112768ULL), + Decimal(5421010862427522LL, 3136633892082024448ULL), + Decimal(54210108624275221LL, 12919594847110692864ULL), + Decimal(542101086242752217LL, 68739955140067328ULL), + Decimal(5421010862427522170LL, 687399551400673280ULL)}; + +inline void ShiftAndAdd(std::string_view input, uint128_t& out) { + for (size_t pos = 0; pos < input.size();) { + const size_t group_size = std::min(kInt64DecimalDigits, input.size() - pos); + const uint64_t multiple = kUInt64PowersOfTen[group_size]; + uint64_t value = 0; + + auto [_, ec] = + std::from_chars(input.data() + pos, input.data() + pos + group_size, value); + ICEBERG_DCHECK(ec == std::errc(), "Failed to parse digits in ShiftAndAdd"); + + out = out * multiple + value; + pos += group_size; + } +} + +void AdjustIntegerStringWithScale(int32_t scale, std::string* str) { + if (scale == 0) { + return; + } + ICEBERG_DCHECK(str != nullptr && !str->empty(), "str must not be null or empty"); + const bool is_negative = str->front() == '-'; + const auto is_negative_offset = static_cast<int32_t>(is_negative); + const auto len = static_cast<int32_t>(str->size()); + const int32_t num_digits = len - is_negative_offset; + const int32_t adjusted_exponent = num_digits - 1 - scale; + + // Note that the -6 is taken from the Java BigDecimal documentation. + if (scale < 0 || adjusted_exponent < -6) { + // Example 1: + // Precondition: *str = "123", is_negative_offset = 0, num_digits = 3, scale = -2, + // adjusted_exponent = 4 + // After inserting decimal point: *str = "1.23" + // After appending exponent: *str = "1.23E+4" + // Example 2: + // Precondition: *str = "-123", is_negative_offset = 1, num_digits = 3, scale = 9, + // adjusted_exponent = -7 + // After inserting decimal point: *str = "-1.23" + // After appending exponent: *str = "-1.23E-7" + // Example 3: + // Precondition: *str = "0", is_negative_offset = 0, num_digits = 1, scale = -1, + // adjusted_exponent = 1 + // After inserting decimal point: *str = "0" // Not inserted + // After appending exponent: *str = "0E+1" + if (num_digits > 1) { + str->insert(str->begin() + 1 + is_negative_offset, '.'); + } + str->push_back('E'); + if (adjusted_exponent >= 0) { + str->push_back('+'); + } + // Append the adjusted exponent as a string. + str->append(std::to_string(adjusted_exponent)); + return; + } + + if (num_digits > scale) { + const auto n = static_cast<size_t>(len - scale); + // Example 1: + // Precondition: *str = "123", len = num_digits = 3, scale = 1, n = 2 + // After inserting decimal point: *str = "12.3" + // Example 2: + // Precondition: *str = "-123", len = 4, num_digits = 3, scale = 1, n = 3 + // After inserting decimal point: *str = "-12.3" + str->insert(str->begin() + n, '.'); + return; + } + + // Example 1: + // Precondition: *str = "123", is_negative_offset = 0, num_digits = 3, scale = 4 + // After insert: *str = "000123" + // After setting decimal point: *str = "0.0123" + // Example 2: + // Precondition: *str = "-123", is_negative_offset = 1, num_digits = 3, scale = 4 + // After insert: *str = "-000123" + // After setting decimal point: *str = "-0.0123" + str->insert(is_negative_offset, scale - num_digits + 2, '0'); + str->at(is_negative_offset + 1) = '.'; +} + +bool RescaleWouldCauseDataLoss(const Decimal& value, int32_t delta_scale, + const Decimal& multiplier, Decimal* result) { + if (delta_scale < 0) { + auto res = value.Divide(multiplier); + ICEBERG_DCHECK(res, "Decimal::Divide failed"); + *result = res->first; + return res->second != 0; + } + + *result = value * multiplier; + return (value < 0) ? *result > value : *result < value; +} + +} // namespace + +Decimal::Decimal(std::string_view str) { + auto result = Decimal::FromString(str); + if (!result) { + throw IcebergError(std::format("Failed to parse Decimal from string: {}, error: {}", + str, result.error().message)); + } + *this = std::move(result.value()); +} + +Decimal& Decimal::Negate() { + uint128_t u = ~static_cast<uint128_t>(data_) + 1; + data_ = static_cast<int128_t>(u); + return *this; +} + +Decimal& Decimal::Abs() { return *this < 0 ? Negate() : *this; } + +Decimal Decimal::Abs(const Decimal& value) { + Decimal result(value); + return result.Abs(); +} + +Decimal& Decimal::operator+=(const Decimal& other) { + data_ += other.data_; + return *this; +} + +Decimal& Decimal::operator-=(const Decimal& other) { + data_ -= other.data_; + return *this; +} + +Decimal& Decimal::operator*=(const Decimal& other) { + data_ *= other.data_; + return *this; +} + +Result<std::pair<Decimal, Decimal>> Decimal::Divide(const Decimal& divisor) const { + std::pair<Decimal, Decimal> result; + if (divisor == 0) { + return Invalid("Cannot divide by zero in Decimal::Divide"); + } + return std::make_pair(*this / divisor, *this % divisor); +} + +Decimal& Decimal::operator/=(const Decimal& other) { + data_ /= other.data_; + return *this; +} + +Decimal& Decimal::operator|=(const Decimal& other) { + data_ |= other.data_; + return *this; +} + +Decimal& Decimal::operator&=(const Decimal& other) { + data_ &= other.data_; + return *this; +} + +Decimal& Decimal::operator<<=(uint32_t bits) { + if (bits != 0) { + data_ = static_cast<int128_t>(static_cast<uint128_t>(data_) << bits); + } + + return *this; +} + +Decimal& Decimal::operator>>=(uint32_t bits) { + if (bits != 0) { + data_ >>= bits; + } + + return *this; +} + +Result<std::string> Decimal::ToString(int32_t scale) const { + if (scale < -kMaxScale || scale > kMaxScale) { + return InvalidArgument( + "Decimal::ToString: scale must be in the range [-{}, {}], was {}", kMaxScale, + kMaxScale, scale); + } + std::string str(ToIntegerString()); + AdjustIntegerStringWithScale(scale, &str); + return str; +} + +std::string Decimal::ToIntegerString() const { + if (data_ == 0) { + return "0"; + } + + bool negative = data_ < 0; + uint128_t uval = + negative ? -static_cast<uint128_t>(data_) : static_cast<uint128_t>(data_); + + constexpr uint32_t k1e9 = 1000000000U; + constexpr size_t kNumBits = 128; + // Segments will contain the array split into groups that map to decimal digits, in + // little endian order. Each segment will hold at most 9 decimal digits. For example, if + // the input represents 9876543210123456789, then segments will be [123456789, + // 876543210, 9]. + // The max number of segments needed = ceil(kNumBits * log(2) / log(1e9)) + // = ceil(kNumBits / 29.897352854) <= ceil(kNumBits / 29). + std::array<uint32_t, (kNumBits + 28) / 29> segments; + size_t num_segments = 0; + + while (uval > 0) { + // Compute remainder = uval % 1e9 and uval = uval / 1e9. + auto remainder = static_cast<uint32_t>(uval % k1e9); + uval /= k1e9; + segments[num_segments++] = remainder; + } + + std::ostringstream oss; + if (negative) { + oss << '-'; + } + + // First segment is formatted as-is. + oss << segments[num_segments - 1]; + + // Remaining segments are formatted with leading zeros to fill 9 digits. e.g. 123 is + // formatted as "000000123" + for (size_t i = num_segments - 1; i-- > 0;) { + oss << std::setw(9) << std::setfill('0') << segments[i]; + } + + return oss.str(); +} + +Result<Decimal> Decimal::FromString(std::string_view str, int32_t* precision, + int32_t* scale) { + if (str.empty()) { + return InvalidArgument("Empty string is not a valid Decimal"); + } + DecimalComponents dec; + if (!ParseDecimalComponents(str, &dec)) { + return InvalidArgument("Invalid decimal string '{}'", str); + } + + // Count number of significant digits (without leading zeros) + size_t first_non_zero = dec.while_digits.find_first_not_of('0'); + size_t significant_digits = dec.fractional_digits.size(); + if (first_non_zero != std::string_view::npos) { + significant_digits += dec.while_digits.size() - first_non_zero; + } + + auto parsed_precision = static_cast<int32_t>(significant_digits); + + int32_t parsed_scale = 0; + if (dec.has_exponent) { + auto adjusted_exponent = dec.exponent; + parsed_scale = static_cast<int32_t>(dec.fractional_digits.size()) - adjusted_exponent; + } else { + parsed_scale = static_cast<int32_t>(dec.fractional_digits.size()); + } + + uint128_t value = 0; + ShiftAndAdd(dec.while_digits, value); + ShiftAndAdd(dec.fractional_digits, value); + Decimal result(static_cast<int128_t>(value)); Review Comment: Thanks for the reminder, will keep in mind, thanks. -- This is an automated message from the Apache Git Service. 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