src/liblzma/common/vli_encoder.c

   1 // SPDX-License-Identifier: 0BSD
   2
   3 ///////////////////////////////////////////////////////////////////////////////
   4 //
   5 /// \file       vli_encoder.c
   6 /// \brief      Encodes variable-length integers
   7 //
   8 //  Author:     Lasse Collin
   9 //
  10 ///////////////////////////////////////////////////////////////////////////////
  11
  12 #include "common.h"
  13
  14
  15 extern LZMA_API(lzma_ret)
  16 lzma_vli_encode(lzma_vli vli, size_t *vli_pos,
  17                 uint8_t *restrict out, size_t *restrict out_pos,
  18                 size_t out_size)
  19 {
  20         // If we haven't been given vli_pos, work in single-call mode.
  21         size_t vli_pos_internal = 0;
  22         if (vli_pos == NULL) {
  23                 vli_pos = &vli_pos_internal;
  24
  25                 // In single-call mode, we expect that the caller has
  26                 // reserved enough output space.
  27                 if (*out_pos >= out_size)
  28                         return LZMA_PROG_ERROR;
  29         } else {
  30                 // This never happens when we are called by liblzma, but
  31                 // may happen if called directly from an application.
  32                 if (*out_pos >= out_size)
  33                         return LZMA_BUF_ERROR;
  34         }
  35
  36         // Validate the arguments.
  37         if (*vli_pos >= LZMA_VLI_BYTES_MAX || vli > LZMA_VLI_MAX)
  38                 return LZMA_PROG_ERROR;
  39
  40         // Shift vli so that the next bits to encode are the lowest. In
  41         // single-call mode this never changes vli since *vli_pos is zero.
  42         vli >>= *vli_pos * 7;
  43
  44         // Write the non-last bytes in a loop.
  45         while (vli >= 0x80) {
  46                 // We don't need *vli_pos during this function call anymore,
  47                 // but update it here so that it is ready if we need to
  48                 // return before the whole integer has been decoded.
  49                 ++*vli_pos;
  50                 assert(*vli_pos < LZMA_VLI_BYTES_MAX);
  51
  52                 // Write the next byte.
  53                 out[*out_pos] = (uint8_t)(vli) | 0x80;
  54                 vli >>= 7;
  55
  56                 if (++*out_pos == out_size)
  57                         return vli_pos == &vli_pos_internal
  58                                         ? LZMA_PROG_ERROR : LZMA_OK;
  59         }
  60
  61         // Write the last byte.
  62         out[*out_pos] = (uint8_t)(vli);
  63         ++*out_pos;
  64         ++*vli_pos;
  65
  66         return vli_pos == &vli_pos_internal ? LZMA_OK : LZMA_STREAM_END;
  67
  68 }