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