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Diffstat (limited to 'absl/strings/internal/str_format/constexpr_parser.h')
| -rw-r--r-- | absl/strings/internal/str_format/constexpr_parser.h | 351 |
1 files changed, 351 insertions, 0 deletions
diff --git a/absl/strings/internal/str_format/constexpr_parser.h b/absl/strings/internal/str_format/constexpr_parser.h new file mode 100644 index 00000000..3dc1776b --- /dev/null +++ b/absl/strings/internal/str_format/constexpr_parser.h @@ -0,0 +1,351 @@ +// Copyright 2022 The Abseil Authors +// +// Licensed 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 +// +// https://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. + +#ifndef ABSL_STRINGS_INTERNAL_STR_FORMAT_CONSTEXPR_PARSER_H_ +#define ABSL_STRINGS_INTERNAL_STR_FORMAT_CONSTEXPR_PARSER_H_ + +#include <cassert> +#include <cstdint> +#include <limits> + +#include "absl/base/const_init.h" +#include "absl/strings/internal/str_format/extension.h" + +namespace absl { +ABSL_NAMESPACE_BEGIN +namespace str_format_internal { + +enum class LengthMod : std::uint8_t { h, hh, l, ll, L, j, z, t, q, none }; + +// The analyzed properties of a single specified conversion. +struct UnboundConversion { + // This is a user defined default constructor on purpose to skip the + // initialization of parts of the object that are not necessary. + UnboundConversion() {} // NOLINT + + // This constructor is provided for the static checker. We don't want to do + // the unnecessary initialization in the normal case. + explicit constexpr UnboundConversion(absl::ConstInitType) + : arg_position{}, width{}, precision{} {} + + class InputValue { + public: + constexpr void set_value(int value) { + assert(value >= 0); + value_ = value; + } + constexpr int value() const { return value_; } + + // Marks the value as "from arg". aka the '*' format. + // Requires `value >= 1`. + // When set, is_from_arg() return true and get_from_arg() returns the + // original value. + // `value()`'s return value is unspecified in this state. + constexpr void set_from_arg(int value) { + assert(value > 0); + value_ = -value - 1; + } + constexpr bool is_from_arg() const { return value_ < -1; } + constexpr int get_from_arg() const { + assert(is_from_arg()); + return -value_ - 1; + } + + private: + int value_ = -1; + }; + + // No need to initialize. It will always be set in the parser. + int arg_position; + + InputValue width; + InputValue precision; + + Flags flags = Flags::kBasic; + LengthMod length_mod = LengthMod::none; + FormatConversionChar conv = FormatConversionCharInternal::kNone; +}; + +// Helper tag class for the table below. +// It allows fast `char -> ConversionChar/LengthMod/Flags` checking and +// conversions. +class ConvTag { + public: + constexpr ConvTag(FormatConversionChar conversion_char) // NOLINT + : tag_(static_cast<uint8_t>(conversion_char)) {} + constexpr ConvTag(LengthMod length_mod) // NOLINT + : tag_(0x80 | static_cast<uint8_t>(length_mod)) {} + constexpr ConvTag(Flags flags) // NOLINT + : tag_(0xc0 | static_cast<uint8_t>(flags)) {} + constexpr ConvTag() : tag_(0xFF) {} + + constexpr bool is_conv() const { return (tag_ & 0x80) == 0; } + constexpr bool is_length() const { return (tag_ & 0xC0) == 0x80; } + constexpr bool is_flags() const { return (tag_ & 0xE0) == 0xC0; } + + constexpr FormatConversionChar as_conv() const { + assert(is_conv()); + assert(!is_length()); + assert(!is_flags()); + return static_cast<FormatConversionChar>(tag_); + } + constexpr LengthMod as_length() const { + assert(!is_conv()); + assert(is_length()); + assert(!is_flags()); + return static_cast<LengthMod>(tag_ & 0x3F); + } + constexpr Flags as_flags() const { + assert(!is_conv()); + assert(!is_length()); + assert(is_flags()); + return static_cast<Flags>(tag_ & 0x1F); + } + + private: + uint8_t tag_; +}; + +struct ConvTagHolder { + using CC = FormatConversionCharInternal; + using LM = LengthMod; + + // Abbreviations to fit in the table below. + static constexpr auto kFSign = Flags::kSignCol; + static constexpr auto kFAlt = Flags::kAlt; + static constexpr auto kFPos = Flags::kShowPos; + static constexpr auto kFLeft = Flags::kLeft; + static constexpr auto kFZero = Flags::kZero; + + static constexpr ConvTag value[256] = { + {}, {}, {}, {}, {}, {}, {}, {}, // 00-07 + {}, {}, {}, {}, {}, {}, {}, {}, // 08-0f + {}, {}, {}, {}, {}, {}, {}, {}, // 10-17 + {}, {}, {}, {}, {}, {}, {}, {}, // 18-1f + kFSign, {}, {}, kFAlt, {}, {}, {}, {}, // !"#$%&' + {}, {}, {}, kFPos, {}, kFLeft, {}, {}, // ()*+,-./ + kFZero, {}, {}, {}, {}, {}, {}, {}, // 01234567 + {}, {}, {}, {}, {}, {}, {}, {}, // 89:;<=>? + {}, CC::A, {}, {}, {}, CC::E, CC::F, CC::G, // @ABCDEFG + {}, {}, {}, {}, LM::L, {}, {}, {}, // HIJKLMNO + {}, {}, {}, {}, {}, {}, {}, {}, // PQRSTUVW + CC::X, {}, {}, {}, {}, {}, {}, {}, // XYZ[\]^_ + {}, CC::a, {}, CC::c, CC::d, CC::e, CC::f, CC::g, // `abcdefg + LM::h, CC::i, LM::j, {}, LM::l, {}, CC::n, CC::o, // hijklmno + CC::p, LM::q, {}, CC::s, LM::t, CC::u, CC::v, {}, // pqrstuvw + CC::x, {}, LM::z, {}, {}, {}, {}, {}, // xyz{|}! + {}, {}, {}, {}, {}, {}, {}, {}, // 80-87 + {}, {}, {}, {}, {}, {}, {}, {}, // 88-8f + {}, {}, {}, {}, {}, {}, {}, {}, // 90-97 + {}, {}, {}, {}, {}, {}, {}, {}, // 98-9f + {}, {}, {}, {}, {}, {}, {}, {}, // a0-a7 + {}, {}, {}, {}, {}, {}, {}, {}, // a8-af + {}, {}, {}, {}, {}, {}, {}, {}, // b0-b7 + {}, {}, {}, {}, {}, {}, {}, {}, // b8-bf + {}, {}, {}, {}, {}, {}, {}, {}, // c0-c7 + {}, {}, {}, {}, {}, {}, {}, {}, // c8-cf + {}, {}, {}, {}, {}, {}, {}, {}, // d0-d7 + {}, {}, {}, {}, {}, {}, {}, {}, // d8-df + {}, {}, {}, {}, {}, {}, {}, {}, // e0-e7 + {}, {}, {}, {}, {}, {}, {}, {}, // e8-ef + {}, {}, {}, {}, {}, {}, {}, {}, // f0-f7 + {}, {}, {}, {}, {}, {}, {}, {}, // f8-ff + }; +}; + +// Keep a single table for all the conversion chars and length modifiers. +constexpr ConvTag GetTagForChar(char c) { + return ConvTagHolder::value[static_cast<unsigned char>(c)]; +} + +constexpr bool CheckFastPathSetting(const UnboundConversion& conv) { + bool width_precision_needed = + conv.width.value() >= 0 || conv.precision.value() >= 0; + if (width_precision_needed && conv.flags == Flags::kBasic) { +#if defined(__clang__) + // Some compilers complain about this in constexpr even when not executed, + // so only enable the error dump in clang. + fprintf(stderr, + "basic=%d left=%d show_pos=%d sign_col=%d alt=%d zero=%d " + "width=%d precision=%d\n", + conv.flags == Flags::kBasic ? 1 : 0, + FlagsContains(conv.flags, Flags::kLeft) ? 1 : 0, + FlagsContains(conv.flags, Flags::kShowPos) ? 1 : 0, + FlagsContains(conv.flags, Flags::kSignCol) ? 1 : 0, + FlagsContains(conv.flags, Flags::kAlt) ? 1 : 0, + FlagsContains(conv.flags, Flags::kZero) ? 1 : 0, conv.width.value(), + conv.precision.value()); +#endif // defined(__clang__) + return false; + } + return true; +} + +constexpr int ParseDigits(char& c, const char*& pos, const char* const end) { + int digits = c - '0'; + // We do not want to overflow `digits` so we consume at most digits10 + // digits. If there are more digits the parsing will fail later on when the + // digit doesn't match the expected characters. + int num_digits = std::numeric_limits<int>::digits10; + for (;;) { + if (ABSL_PREDICT_FALSE(pos == end)) break; + c = *pos++; + if ('0' > c || c > '9') break; + --num_digits; + if (ABSL_PREDICT_FALSE(!num_digits)) break; + digits = 10 * digits + c - '0'; + } + return digits; +} + +template <bool is_positional> +constexpr const char* ConsumeConversion(const char* pos, const char* const end, + UnboundConversion* conv, + int* next_arg) { + const char* const original_pos = pos; + char c = 0; + // Read the next char into `c` and update `pos`. Returns false if there are + // no more chars to read. +#define ABSL_FORMAT_PARSER_INTERNAL_GET_CHAR() \ + do { \ + if (ABSL_PREDICT_FALSE(pos == end)) return nullptr; \ + c = *pos++; \ + } while (0) + + if (is_positional) { + ABSL_FORMAT_PARSER_INTERNAL_GET_CHAR(); + if (ABSL_PREDICT_FALSE(c < '1' || c > '9')) return nullptr; + conv->arg_position = ParseDigits(c, pos, end); + assert(conv->arg_position > 0); + if (ABSL_PREDICT_FALSE(c != '$')) return nullptr; + } + + ABSL_FORMAT_PARSER_INTERNAL_GET_CHAR(); + + // We should start with the basic flag on. + assert(conv->flags == Flags::kBasic); + + // Any non alpha character makes this conversion not basic. + // This includes flags (-+ #0), width (1-9, *) or precision (.). + // All conversion characters and length modifiers are alpha characters. + if (c < 'A') { + while (c <= '0') { + auto tag = GetTagForChar(c); + if (tag.is_flags()) { + conv->flags = conv->flags | tag.as_flags(); + ABSL_FORMAT_PARSER_INTERNAL_GET_CHAR(); + } else { + break; + } + } + + if (c <= '9') { + if (c >= '0') { + int maybe_width = ParseDigits(c, pos, end); + if (!is_positional && c == '$') { + if (ABSL_PREDICT_FALSE(*next_arg != 0)) return nullptr; + // Positional conversion. + *next_arg = -1; + return ConsumeConversion<true>(original_pos, end, conv, next_arg); + } + conv->flags = conv->flags | Flags::kNonBasic; + conv->width.set_value(maybe_width); + } else if (c == '*') { + conv->flags = conv->flags | Flags::kNonBasic; + ABSL_FORMAT_PARSER_INTERNAL_GET_CHAR(); + if (is_positional) { + if (ABSL_PREDICT_FALSE(c < '1' || c > '9')) return nullptr; + conv->width.set_from_arg(ParseDigits(c, pos, end)); + if (ABSL_PREDICT_FALSE(c != '$')) return nullptr; + ABSL_FORMAT_PARSER_INTERNAL_GET_CHAR(); + } else { + conv->width.set_from_arg(++*next_arg); + } + } + } + + if (c == '.') { + conv->flags = conv->flags | Flags::kNonBasic; + ABSL_FORMAT_PARSER_INTERNAL_GET_CHAR(); + if ('0' <= c && c <= '9') { + conv->precision.set_value(ParseDigits(c, pos, end)); + } else if (c == '*') { + ABSL_FORMAT_PARSER_INTERNAL_GET_CHAR(); + if (is_positional) { + if (ABSL_PREDICT_FALSE(c < '1' || c > '9')) return nullptr; + conv->precision.set_from_arg(ParseDigits(c, pos, end)); + if (c != '$') return nullptr; + ABSL_FORMAT_PARSER_INTERNAL_GET_CHAR(); + } else { + conv->precision.set_from_arg(++*next_arg); + } + } else { + conv->precision.set_value(0); + } + } + } + + auto tag = GetTagForChar(c); + + if (ABSL_PREDICT_FALSE(c == 'v' && conv->flags != Flags::kBasic)) { + return nullptr; + } + + if (ABSL_PREDICT_FALSE(!tag.is_conv())) { + if (ABSL_PREDICT_FALSE(!tag.is_length())) return nullptr; + + // It is a length modifier. + using str_format_internal::LengthMod; + LengthMod length_mod = tag.as_length(); + ABSL_FORMAT_PARSER_INTERNAL_GET_CHAR(); + if (c == 'h' && length_mod == LengthMod::h) { + conv->length_mod = LengthMod::hh; + ABSL_FORMAT_PARSER_INTERNAL_GET_CHAR(); + } else if (c == 'l' && length_mod == LengthMod::l) { + conv->length_mod = LengthMod::ll; + ABSL_FORMAT_PARSER_INTERNAL_GET_CHAR(); + } else { + conv->length_mod = length_mod; + } + tag = GetTagForChar(c); + + if (ABSL_PREDICT_FALSE(c == 'v')) return nullptr; + if (ABSL_PREDICT_FALSE(!tag.is_conv())) return nullptr; + } + + assert(CheckFastPathSetting(*conv)); + (void)(&CheckFastPathSetting); + + conv->conv = tag.as_conv(); + if (!is_positional) conv->arg_position = ++*next_arg; + return pos; +} + +// Consume conversion spec prefix (not including '%') of [p, end) if valid. +// Examples of valid specs would be e.g.: "s", "d", "-12.6f". +// If valid, it returns the first character following the conversion spec, +// and the spec part is broken down and returned in 'conv'. +// If invalid, returns nullptr. +constexpr const char* ConsumeUnboundConversion(const char* p, const char* end, + UnboundConversion* conv, + int* next_arg) { + if (*next_arg < 0) return ConsumeConversion<true>(p, end, conv, next_arg); + return ConsumeConversion<false>(p, end, conv, next_arg); +} + +} // namespace str_format_internal +ABSL_NAMESPACE_END +} // namespace absl + +#endif // ABSL_STRINGS_INTERNAL_STR_FORMAT_CONSTEXPR_PARSER_H_ |