libc/src/stdio/printf_core/parser.h

//===-- Format string parser for printf -------------------------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_LIBC_SRC_STDIO_PRINTF_CORE_PARSER_H
#define LLVM_LIBC_SRC_STDIO_PRINTF_CORE_PARSER_H

#include "src/__support/CPP/type_traits.h"
#include "src/__support/arg_list.h"
#include "src/stdio/printf_core/core_structs.h"
#include "src/stdio/printf_core/printf_config.h"

#include <stddef.h>

namespace __llvm_libc {
namespace printf_core {

class Parser {
  const char *__restrict str;

  size_t cur_pos = 0;
  internal::ArgList args_cur;

#ifndef LLVM_LIBC_PRINTF_DISABLE_INDEX_MODE
  // args_start stores the start of the va_args, which is allows getting the
  // value of arguments that have already been passed. args_index is tracked so
  // that we know which argument args_cur is on.
  internal::ArgList args_start;
  size_t args_index = 1;

  enum PrimaryType : uint8_t { Integer = 0, Float = 1, Pointer = 2 };

  // TypeDesc stores the information about a type that is relevant to printf in
  // a relatively compact manner.
  struct TypeDesc {
    uint8_t size;
    PrimaryType primary_type;
    constexpr bool operator==(const TypeDesc &other) const {
      return (size == other.size) && (primary_type == other.primary_type);
    }
  };

  // Defined in printf_config.h
  static constexpr size_t DESC_ARR_LEN = LLVM_LIBC_PRINTF_INDEX_ARR_LEN;

  // desc_arr stores the sizes of the variables in the ArgList. This is used in
  // index mode to reduce repeated string parsing. The sizes are stored as
  // TypeDesc objects, which store the size as well as minimal type information.
  // This is necessary because some systems separate the floating point and
  // integer values in va_args.
  TypeDesc desc_arr[DESC_ARR_LEN] = {{0, Integer}};

  // TODO: Look into object stores for optimization.

#endif // LLVM_LIBC_PRINTF_DISABLE_INDEX_MODE

public:
#ifndef LLVM_LIBC_PRINTF_DISABLE_INDEX_MODE
  Parser(const char *__restrict new_str, internal::ArgList &args)
      : str(new_str), args_cur(args), args_start(args) {}
#else
  Parser(const char *__restrict new_str, internal::ArgList &args)
      : str(new_str), args_cur(args) {}
#endif // LLVM_LIBC_PRINTF_DISABLE_INDEX_MODE

  // get_next_section will parse the format string until it has a fully
  // specified format section. This can either be a raw format section with no
  // conversion, or a format section with a conversion that has all of its
  // variables stored in the format section.
  FormatSection get_next_section();

private:
  // parse_flags parses the flags inside a format string. It assumes that
  // str[*local_pos] is inside a format specifier, and parses any flags it
  // finds. It returns a FormatFlags object containing the set of found flags
  // arithmetically or'd together. local_pos will be moved past any flags found.
  FormatFlags parse_flags(size_t *local_pos);

  // parse_length_modifier parses the length modifier inside a format string. It
  // assumes that str[*local_pos] is inside a format specifier. It returns a
  // LengthModifier with the length modifier it found. It will advance local_pos
  // after the format specifier if one is found.
  LengthModifier parse_length_modifier(size_t *local_pos);

  // get_next_arg_value gets the next value from the arg list as type T.
  template <class T> T inline get_next_arg_value() {
    return args_cur.next_var<T>();
  }

  //----------------------------------------------------
  // INDEX MODE ONLY FUNCTIONS AFTER HERE:
  //----------------------------------------------------

#ifndef LLVM_LIBC_PRINTF_DISABLE_INDEX_MODE

  // parse_index parses the index of a value inside a format string. It
  // assumes that str[*local_pos] points to character after a '%' or '*', and
  // returns 0 if there is no closing $, or if it finds no number. If it finds a
  // number, it will move local_pos past the end of the $, else it will not move
  // local_pos.
  size_t parse_index(size_t *local_pos);

  template <typename T> static constexpr TypeDesc get_type_desc() {
    if constexpr (cpp::is_same_v<T, void>) {
      return TypeDesc{0, PrimaryType::Integer};
    } else {
      constexpr bool isPointer = cpp::is_same_v<T, void *>;
      constexpr bool isFloat =
          cpp::is_same_v<T, double> || cpp::is_same_v<T, long double>;
      return TypeDesc{sizeof(T), isPointer ? PrimaryType::Pointer
                                 : isFloat ? PrimaryType::Float
                                           : PrimaryType::Integer};
    }
  }

  void inline set_type_desc(size_t index, TypeDesc value) {
    if (index != 0 && index <= DESC_ARR_LEN)
      desc_arr[index - 1] = value;
  }

  // get_arg_value gets the value from the arg list at index (starting at 1).
  // This may require parsing the format string. An index of 0 is interpreted as
  // the next value.
  template <class T> T inline get_arg_value(size_t index) {
    if (!(index == 0 || index == args_index))
      args_to_index(index);

    set_type_desc(index, get_type_desc<T>());

    ++args_index;
    return get_next_arg_value<T>();
  }

  // the ArgList can only return the next item in the list. This function is
  // used in index mode when the item that needs to be read is not the next one.
  // It moves cur_args to the index requested so the the appropriate value may
  // be read. This may involve parsing the format string, and is in the worst
  // case an O(n^2) operation.
  void args_to_index(size_t index);

  // get_type_desc assumes that this format string uses index mode. It iterates
  // through the format string until it finds a format specifier that defines
  // the type of index, and returns a TypeDesc describing that type. It does not
  // modify cur_pos.
  TypeDesc get_type_desc(size_t index);

#endif // LLVM_LIBC_PRINTF_DISABLE_INDEX_MODE
};

} // namespace printf_core
} // namespace __llvm_libc

#endif // LLVM_LIBC_SRC_STDIO_PRINTF_CORE_PARSER_H