zhjwpku commented on code in PR #182: URL: https://github.com/apache/iceberg-cpp/pull/182#discussion_r2319396290
########## src/iceberg/util/decimal.cc: ########## @@ -0,0 +1,1044 @@ +/* + * 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 <array> +#include <bit> +#include <cassert> +#include <charconv> +#include <climits> +#include <cmath> +#include <cstdint> +#include <cstring> +#include <format> +#include <iomanip> +#include <limits> +#include <sstream> +#include <string> +#include <string_view> +#include <utility> + +#include "iceberg/result.h" +#include "iceberg/util/int128.h" +#include "iceberg/util/macros.h" + +namespace iceberg { + +namespace { + +// Signed left shift with well-defined behaviour on negative numbers or overflow +template <typename SignedInt, typename Shift> + requires std::is_signed_v<SignedInt> && std::is_integral_v<Shift> +constexpr SignedInt SafeLeftShift(SignedInt u, Shift shift) { + using UnsignedInt = std::make_unsigned_t<SignedInt>; + return static_cast<SignedInt>(static_cast<UnsignedInt>(u) << shift); +} + +struct DecimalComponents { + std::string_view while_digits; + std::string_view fractional_digits; + int32_t exponent; + 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])) { + ++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)}; + +static 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; + + std::from_chars(input.data() + pos, input.data() + pos + group_size, value); + + out = out * multiple + value; + pos += group_size; + } +} + +static void AdjustIntegerStringWithScale(std::string* str, int32_t scale) { + if (scale == 0) { + return; + } + assert(str != nullptr); Review Comment: Added. -- This is an automated message from the Apache Git Service. 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