libc/src/__support/StringUtil/message_mapper.h

   1 //===-- A class for number to string mappings -------------------*- C++ -*-===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #ifndef LLVM_LIBC_SRC___SUPPORT_STRING_UTIL_MESSAGE_MAPPER_H
  10 #define LLVM_LIBC_SRC___SUPPORT_STRING_UTIL_MESSAGE_MAPPER_H
  11
  12 #include "src/__support/CPP/array.h"
  13 #include "src/__support/CPP/optional.h"
  14 #include "src/__support/CPP/string_view.h"
  15 #include <stddef.h>
  16
  17 namespace LIBC_NAMESPACE {
  18
  19 struct MsgMapping {
  20   int num;
  21   cpp::string_view msg;
  22
  23   constexpr MsgMapping() : num(0), msg() { ; }
  24
  25   constexpr MsgMapping(int init_num, const char *init_msg)
  26       : num(init_num), msg(init_msg) {
  27     ;
  28   }
  29 };
  30
  31 template <size_t N> using MsgTable = cpp::array<MsgMapping, N>;
  32
  33 template <size_t N> constexpr size_t total_str_len(const MsgTable<N> &table) {
  34   size_t total = 0;
  35   for (size_t i = 0; i < table.size(); ++i) {
  36     // add 1 for the null terminator.
  37     total += table[i].msg.size() + 1;
  38   }
  39   return total;
  40 }
  41
  42 template <size_t N> constexpr size_t max_key_val(const MsgTable<N> &table) {
  43   int max = 0;
  44   for (size_t i = 0; i < table.size(); ++i) {
  45     if (table[i].num > max) {
  46       max = table[i].num;
  47     }
  48   }
  49   // max will never be negative since the starting value is 0. This is good,
  50   // since it's used as a length.
  51   return static_cast<size_t>(max);
  52 }
  53
  54 template <size_t ARR_SIZE, size_t TOTAL_STR_LEN> class MessageMapper {
  55   int msg_offsets[ARR_SIZE] = {-1};
  56   char string_array[TOTAL_STR_LEN] = {'\0'};
  57
  58 public:
  59   template <size_t N> constexpr MessageMapper(const MsgTable<N> &table) {
  60     cpp::string_view string_mappings[ARR_SIZE] = {""};
  61     for (size_t i = 0; i < table.size(); ++i)
  62       string_mappings[table[i].num] = table[i].msg;
  63
  64     int string_array_index = 0;
  65     for (size_t cur_num = 0; cur_num < ARR_SIZE; ++cur_num) {
  66       if (string_mappings[cur_num].size() != 0) {
  67         msg_offsets[cur_num] = string_array_index;
  68         // No need to replace with proper strcpy, this is evaluated at compile
  69         // time.
  70         for (size_t i = 0; i < string_mappings[cur_num].size() + 1;
  71              ++i, ++string_array_index) {
  72           string_array[string_array_index] = string_mappings[cur_num][i];
  73         }
  74       } else {
  75         msg_offsets[cur_num] = -1;
  76       }
  77     }
  78   }
  79
  80   cpp::optional<cpp::string_view> get_str(int num) const {
  81     if (num >= 0 && static_cast<size_t>(num) < ARR_SIZE &&
  82         msg_offsets[num] != -1) {
  83       return {string_array + msg_offsets[num]};
  84     } else {
  85       return cpp::optional<cpp::string_view>();
  86     }
  87   }
  88 };
  89
  90 template <size_t N1, size_t N2>
  91 constexpr MsgTable<N1 + N2> operator+(const MsgTable<N1> &t1,
  92                                       const MsgTable<N2> &t2) {
  93   MsgTable<N1 + N2> res{};
  94   for (size_t i = 0; i < N1; ++i)
  95     res[i] = t1[i];
  96   for (size_t i = 0; i < N2; ++i)
  97     res[N1 + i] = t2[i];
  98   return res;
  99 }
 100
 101 } // namespace LIBC_NAMESPACE
 102
 103 #endif // LLVM_LIBC_SRC___SUPPORT_STRING_UTIL_MESSAGE_MAPPER_H