src/liblzma/common/vli_encoder.c

   1 ///////////////////////////////////////////////////////////////////////////////
   2 //
   3 /// \file       vli_encoder.c
   4 /// \brief      Encodes variable-length integers
   5 //
   6 //  Author:     Lasse Collin
   7 //
   8 //  This file has been put into the public domain.
   9 //  You can do whatever you want with this file.
  10 //
  11 ///////////////////////////////////////////////////////////////////////////////
  12
  13 #include "common.h"
  14
  15
  16 extern LZMA_API(lzma_ret)
  17 lzma_vli_encode(lzma_vli vli, size_t *vli_pos,
  18                 uint8_t *restrict out, size_t *restrict out_pos,
  19                 size_t out_size)
  20 {
  21         // If we haven't been given vli_pos, work in single-call mode.
  22         size_t vli_pos_internal = 0;
  23         if (vli_pos == NULL) {
  24                 vli_pos = &vli_pos_internal;
  25
  26                 // In single-call mode, we expect that the caller has
  27                 // reserved enough output space.
  28                 if (*out_pos >= out_size)
  29                         return LZMA_PROG_ERROR;
  30         } else {
  31                 // This never happens when we are called by liblzma, but
  32                 // may happen if called directly from an application.
  33                 if (*out_pos >= out_size)
  34                         return LZMA_BUF_ERROR;
  35         }
  36
  37         // Validate the arguments.
  38         if (*vli_pos >= LZMA_VLI_BYTES_MAX || vli > LZMA_VLI_MAX)
  39                 return LZMA_PROG_ERROR;
  40
  41         // Shift vli so that the next bits to encode are the lowest. In
  42         // single-call mode this never changes vli since *vli_pos is zero.
  43         vli >>= *vli_pos * 7;
  44
  45         // Write the non-last bytes in a loop.
  46         while (vli >= 0x80) {
  47                 // We don't need *vli_pos during this function call anymore,
  48                 // but update it here so that it is ready if we need to
  49                 // return before the whole integer has been decoded.
  50                 ++*vli_pos;
  51                 assert(*vli_pos < LZMA_VLI_BYTES_MAX);
  52
  53                 // Write the next byte.
  54                 out[*out_pos] = (uint8_t)(vli) | 0x80;
  55                 vli >>= 7;
  56
  57                 if (++*out_pos == out_size)
  58                         return vli_pos == &vli_pos_internal
  59                                         ? LZMA_PROG_ERROR : LZMA_OK;
  60         }
  61
  62         // Write the last byte.
  63         out[*out_pos] = (uint8_t)(vli);
  64         ++*out_pos;
  65         ++*vli_pos;
  66
  67         return vli_pos == &vli_pos_internal ? LZMA_OK : LZMA_STREAM_END;
  68
  69 }