src/liblzma/api/lzma/vli.h

   1 /**
   2  * \file        lzma/vli.h
   3  * \brief       Variable-length integer handling
   4  *
   5  * In the .xz format, most integers are encoded in a variable-length
   6  * representation, which is sometimes called little endian base-128 encoding.
   7  * This saves space when smaller values are more likely than bigger values.
   8  *
   9  * The encoding scheme encodes seven bits to every byte, using minimum
  10  * number of bytes required to represent the given value. Encodings that use
  11  * non-minimum number of bytes are invalid, thus every integer has exactly
  12  * one encoded representation. The maximum number of bits in a VLI is 63,
  13  * thus the vli argument must be less than or equal to UINT64_MAX / 2. You
  14  * should use LZMA_VLI_MAX for clarity.
  15  */
  16
  17 /*
  18  * Author: Lasse Collin
  19  *
  20  * This file has been put into the public domain.
  21  * You can do whatever you want with this file.
  22  *
  23  * See ../lzma.h for information about liblzma as a whole.
  24  */
  25
  26 #ifndef LZMA_H_INTERNAL
  27 #       error Never include this file directly. Use <lzma.h> instead.
  28 #endif
  29
  30
  31 /**
  32  * \brief       Maximum supported value of a variable-length integer
  33  */
  34 #define LZMA_VLI_MAX (UINT64_MAX / 2)
  35
  36 /**
  37  * \brief       VLI value to denote that the value is unknown
  38  */
  39 #define LZMA_VLI_UNKNOWN UINT64_MAX
  40
  41 /**
  42  * \brief       Maximum supported encoded length of variable length integers
  43  */
  44 #define LZMA_VLI_BYTES_MAX 9
  45
  46 /**
  47  * \brief       VLI constant suffix
  48  */
  49 #define LZMA_VLI_C(n) UINT64_C(n)
  50
  51
  52 /**
  53  * \brief       Variable-length integer type
  54  *
  55  * Valid VLI values are in the range [0, LZMA_VLI_MAX]. Unknown value is
  56  * indicated with LZMA_VLI_UNKNOWN, which is the maximum value of the
  57  * underlaying integer type.
  58  *
  59  * lzma_vli will be uint64_t for the foreseeable future. If a bigger size
  60  * is needed in the future, it is guaranteed that 2 * LZMA_VLI_MAX will
  61  * not overflow lzma_vli. This simplifies integer overflow detection.
  62  */
  63 typedef uint64_t lzma_vli;
  64
  65
  66 /**
  67  * \brief       Validate a variable-length integer
  68  *
  69  * This is useful to test that application has given acceptable values
  70  * for example in the uncompressed_size and compressed_size variables.
  71  *
  72  * \return      True if the integer is representable as VLI or if it
  73  *              indicates unknown value.
  74  */
  75 #define lzma_vli_is_valid(vli) \
  76         ((vli) <= LZMA_VLI_MAX || (vli) == LZMA_VLI_UNKNOWN)
  77
  78
  79 /**
  80  * \brief       Encode a variable-length integer
  81  *
  82  * This function has two modes: single-call and multi-call. Single-call mode
  83  * encodes the whole integer at once; it is an error if the output buffer is
  84  * too small. Multi-call mode saves the position in *vli_pos, and thus it is
  85  * possible to continue encoding if the buffer becomes full before the whole
  86  * integer has been encoded.
  87  *
  88  * \param       vli       Integer to be encoded
  89  * \param       vli_pos   How many VLI-encoded bytes have already been written
  90  *                        out. When starting to encode a new integer in
  91  *                        multi-call mode, *vli_pos must be set to zero.
  92  *                        To use single-call encoding, set vli_pos to NULL.
  93  * \param       out       Beginning of the output buffer
  94  * \param       out_pos   The next byte will be written to out[*out_pos].
  95  * \param       out_size  Size of the out buffer; the first byte into
  96  *                        which no data is written to is out[out_size].
  97  *
  98  * \return      Slightly different return values are used in multi-call and
  99  *              single-call modes.
 100  *
 101  *              Single-call (vli_pos == NULL):
 102  *              - LZMA_OK: Integer successfully encoded.
 103  *              - LZMA_PROG_ERROR: Arguments are not sane. This can be due
 104  *                to too little output space; single-call mode doesn't use
 105  *                LZMA_BUF_ERROR, since the application should have checked
 106  *                the encoded size with lzma_vli_size().
 107  *
 108  *              Multi-call (vli_pos != NULL):
 109  *              - LZMA_OK: So far all OK, but the integer is not
 110  *                completely written out yet.
 111  *              - LZMA_STREAM_END: Integer successfully encoded.
 112  *              - LZMA_BUF_ERROR: No output space was provided.
 113  *              - LZMA_PROG_ERROR: Arguments are not sane.
 114  */
 115 extern LZMA_API(lzma_ret) lzma_vli_encode(lzma_vli vli, size_t *vli_pos,
 116                 uint8_t *out, size_t *out_pos, size_t out_size) lzma_nothrow;
 117
 118
 119 /**
 120  * \brief       Decode a variable-length integer
 121  *
 122  * Like lzma_vli_encode(), this function has single-call and multi-call modes.
 123  *
 124  * \param       vli       Pointer to decoded integer. The decoder will
 125  *                        initialize it to zero when *vli_pos == 0, so
 126  *                        application isn't required to initialize *vli.
 127  * \param       vli_pos   How many bytes have already been decoded. When
 128  *                        starting to decode a new integer in multi-call
 129  *                        mode, *vli_pos must be initialized to zero. To
 130  *                        use single-call decoding, set vli_pos to NULL.
 131  * \param       in        Beginning of the input buffer
 132  * \param       in_pos    The next byte will be read from in[*in_pos].
 133  * \param       in_size   Size of the input buffer; the first byte that
 134  *                        won't be read is in[in_size].
 135  *
 136  * \return      Slightly different return values are used in multi-call and
 137  *              single-call modes.
 138  *
 139  *              Single-call (vli_pos == NULL):
 140  *              - LZMA_OK: Integer successfully decoded.
 141  *              - LZMA_DATA_ERROR: Integer is corrupt. This includes hitting
 142  *                the end of the input buffer before the whole integer was
 143  *                decoded; providing no input at all will use LZMA_DATA_ERROR.
 144  *              - LZMA_PROG_ERROR: Arguments are not sane.
 145  *
 146  *              Multi-call (vli_pos != NULL):
 147  *              - LZMA_OK: So far all OK, but the integer is not
 148  *                completely decoded yet.
 149  *              - LZMA_STREAM_END: Integer successfully decoded.
 150  *              - LZMA_DATA_ERROR: Integer is corrupt.
 151  *              - LZMA_BUF_ERROR: No input was provided.
 152  *              - LZMA_PROG_ERROR: Arguments are not sane.
 153  */
 154 extern LZMA_API(lzma_ret) lzma_vli_decode(lzma_vli *vli, size_t *vli_pos,
 155                 const uint8_t *in, size_t *in_pos, size_t in_size)
 156                 lzma_nothrow;
 157
 158
 159 /**
 160  * \brief       Get the number of bytes required to encode a VLI
 161  *
 162  * \return      Number of bytes on success (1-9). If vli isn't valid,
 163  *              zero is returned.
 164  */
 165 extern LZMA_API(uint32_t) lzma_vli_size(lzma_vli vli)
 166                 lzma_nothrow lzma_attr_pure;