libcxx/src/support/ibm/mbsnrtowcs.cpp

   1 //===----------------------------------------------------------------------===//
   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 #include <cstddef>  // size_t
  10 #include <cwchar>   // mbstate_t
  11 #include <limits.h> // MB_LEN_MAX
  12 #include <string.h> // wmemcpy
  13
  14 // Returns the number of wide characters found in the multi byte sequence `src`
  15 // (of `src_size_bytes`), that fit in the buffer `dst` (of `max_dest_chars`
  16 // elements size). The count returned excludes the null terminator.
  17 // When `dst` is NULL, no characters are copied to `dst`.
  18 // Returns (size_t) -1 when an invalid sequence is encountered.
  19 // Leaves *`src` pointing to the next character to convert or NULL
  20 // if a null character was converted from *`src`.
  21 _LIBCPP_EXPORTED_FROM_ABI size_t mbsnrtowcs(
  22     wchar_t* __restrict dst,
  23     const char** __restrict src,
  24     size_t src_size_bytes,
  25     size_t max_dest_chars,
  26     mbstate_t* __restrict ps) {
  27   const size_t terminated_sequence = static_cast<size_t>(0);
  28   const size_t invalid_sequence    = static_cast<size_t>(-1);
  29   const size_t incomplete_sequence = static_cast<size_t>(-2);
  30
  31   size_t source_converted;
  32   size_t dest_converted;
  33   size_t result = 0;
  34
  35   // If `dst` is null then `max_dest_chars` should be ignored according to the
  36   // standard. Setting `max_dest_chars` to a large value has this effect.
  37   if (dst == nullptr)
  38     max_dest_chars = static_cast<size_t>(-1);
  39
  40   for (dest_converted = source_converted = 0;
  41        source_converted < src_size_bytes && (!dst || dest_converted < max_dest_chars);
  42        ++dest_converted, source_converted += result) {
  43     // Converts one multi byte character.
  44     // If result (char_size) is greater than 0, it's the size in bytes of that character.
  45     // If result (char_size) is zero, it indicates that the null character has been found.
  46     // Otherwise, it's an error and errno may be set.
  47     size_t source_remaining = src_size_bytes - source_converted;
  48     size_t dest_remaining   = max_dest_chars - dest_converted;
  49
  50     if (dst == nullptr) {
  51       result = mbrtowc(nullptr, *src + source_converted, source_remaining, ps);
  52     } else if (dest_remaining >= source_remaining) {
  53       // dst has enough space to translate in-place.
  54       result = mbrtowc(dst + dest_converted, *src + source_converted, source_remaining, ps);
  55     } else {
  56       /*
  57        * dst may not have enough space, so use a temporary buffer.
  58        *
  59        * We need to save a copy of the conversion state
  60        * here so we can restore it if the multibyte
  61        * character is too long for the buffer.
  62        */
  63       wchar_t buff[MB_LEN_MAX];
  64       mbstate_t mbstate_tmp;
  65
  66       if (ps != nullptr)
  67         mbstate_tmp = *ps;
  68       result = mbrtowc(buff, *src + source_converted, source_remaining, ps);
  69
  70       if (result > dest_remaining) {
  71         // Multi-byte sequence for character won't fit.
  72         if (ps != nullptr)
  73           *ps = mbstate_tmp;
  74         break;
  75       } else {
  76         // The buffer was used, so we need copy the translation to dst.
  77         wmemcpy(dst, buff, result);
  78       }
  79     }
  80
  81     // Don't do anything to change errno from here on.
  82     if (result == invalid_sequence || result == terminated_sequence || result == incomplete_sequence) {
  83       break;
  84     }
  85   }
  86
  87   if (dst) {
  88     if (result == terminated_sequence)
  89       *src = nullptr;
  90     else
  91       *src += source_converted;
  92   }
  93   if (result == invalid_sequence)
  94     return invalid_sequence;
  95
  96   return dest_converted;
  97 }