1 /////////////////////////////////////////////////////////////////////////////// 2 // 3 /// \file vli_decoder.c 4 /// \brief Decodes 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_decode(lzma_vli *restrict vli, size_t *vli_pos, 18 const uint8_t *restrict in, size_t *restrict in_pos, 19 size_t in_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 *vli = 0; 26 27 // If there's no input, use LZMA_DATA_ERROR. This way it is 28 // easy to decode VLIs from buffers that have known size, 29 // and get the correct error code in case the buffer is 30 // too short. 31 if (*in_pos >= in_size) 32 return LZMA_DATA_ERROR; 33 34 } else { 35 // Initialize *vli when starting to decode a new integer. 36 if (*vli_pos == 0) 37 *vli = 0; 38 39 // Validate the arguments. 40 if (*vli_pos >= LZMA_VLI_BYTES_MAX 41 || (*vli >> (*vli_pos * 7)) != 0) 42 return LZMA_PROG_ERROR;; 43 44 if (*in_pos >= in_size) 45 return LZMA_BUF_ERROR; 46 } 47 48 do { 49 // Read the next byte. Use a temporary variable so that we 50 // can update *in_pos immediately. 51 const uint8_t byte = in[*in_pos]; 52 ++*in_pos; 53 54 // Add the newly read byte to *vli. 55 *vli += (lzma_vli)(byte & 0x7F) << (*vli_pos * 7); 56 ++*vli_pos; 57 58 // Check if this is the last byte of a multibyte integer. 59 if ((byte & 0x80) == 0) { 60 // We don't allow using variable-length integers as 61 // padding i.e. the encoding must use the most the 62 // compact form. 63 if (byte == 0x00 && *vli_pos > 1) 64 return LZMA_DATA_ERROR; 65 66 return vli_pos == &vli_pos_internal 67 ? LZMA_OK : LZMA_STREAM_END; 68 } 69 70 // There is at least one more byte coming. If we have already 71 // read maximum number of bytes, the integer is considered 72 // corrupt. 73 // 74 // If we need bigger integers in future, old versions liblzma 75 // will confusingly indicate the file being corrupt instead of 76 // unsupported. I suppose it's still better this way, because 77 // in the foreseeable future (writing this in 2008) the only 78 // reason why files would appear having over 63-bit integers 79 // is that the files are simply corrupt. 80 if (*vli_pos == LZMA_VLI_BYTES_MAX) 81 return LZMA_DATA_ERROR; 82 83 } while (*in_pos < in_size); 84 85 return vli_pos == &vli_pos_internal ? LZMA_DATA_ERROR : LZMA_OK; 86 } 87