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// SPDX-License-Identifier: 0BSD
///////////////////////////////////////////////////////////////////////////////
//
/// \file vli_decoder.c
/// \brief Decodes variable-length integers
//
// Author: Lasse Collin
//
///////////////////////////////////////////////////////////////////////////////
#include "common.h"
extern LZMA_API(lzma_ret)
lzma_vli_decode(lzma_vli *restrict vli, size_t *vli_pos,
const uint8_t *restrict in, size_t *restrict in_pos,
size_t in_size)
{
// If we haven't been given vli_pos, work in single-call mode.
size_t vli_pos_internal = 0;
if (vli_pos == NULL) {
vli_pos = &vli_pos_internal;
*vli = 0;
// If there's no input, use LZMA_DATA_ERROR. This way it is
// easy to decode VLIs from buffers that have known size,
// and get the correct error code in case the buffer is
// too short.
if (*in_pos >= in_size)
return LZMA_DATA_ERROR;
} else {
// Initialize *vli when starting to decode a new integer.
if (*vli_pos == 0)
*vli = 0;
// Validate the arguments.
if (*vli_pos >= LZMA_VLI_BYTES_MAX
|| (*vli >> (*vli_pos * 7)) != 0)
return LZMA_PROG_ERROR;;
if (*in_pos >= in_size)
return LZMA_BUF_ERROR;
}
do {
// Read the next byte. Use a temporary variable so that we
// can update *in_pos immediately.
const uint8_t byte = in[*in_pos];
++*in_pos;
// Add the newly read byte to *vli.
*vli += (lzma_vli)(byte & 0x7F) << (*vli_pos * 7);
++*vli_pos;
// Check if this is the last byte of a multibyte integer.
if ((byte & 0x80) == 0) {
// We don't allow using variable-length integers as
// padding i.e. the encoding must use the most the
// compact form.
if (byte == 0x00 && *vli_pos > 1)
return LZMA_DATA_ERROR;
return vli_pos == &vli_pos_internal
? LZMA_OK : LZMA_STREAM_END;
}
// There is at least one more byte coming. If we have already
// read maximum number of bytes, the integer is considered
// corrupt.
//
// If we need bigger integers in future, old versions liblzma
// will confusingly indicate the file being corrupt instead of
// unsupported. I suppose it's still better this way, because
// in the foreseeable future (writing this in 2008) the only
// reason why files would appear having over 63-bit integers
// is that the files are simply corrupt.
if (*vli_pos == LZMA_VLI_BYTES_MAX)
return LZMA_DATA_ERROR;
} while (*in_pos < in_size);
return vli_pos == &vli_pos_internal ? LZMA_DATA_ERROR : LZMA_OK;
}
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