X-Git-Url: https://pd.if.org/git/?a=blobdiff_plain;f=lzma%2Fcommon%2Fvli_decoder.c;fp=lzma%2Fcommon%2Fvli_decoder.c;h=c181828bf5644cf10a37e9382a8b81222b6a2279;hb=32b8a6b26ed8843828e03e505d2256960bda0980;hp=0000000000000000000000000000000000000000;hpb=d48fc23a4bcf8ca3c406d6e8c8a6f8c6b0fa2f1e;p=zpackage

diff --git a/lzma/common/vli_decoder.c b/lzma/common/vli_decoder.c
new file mode 100644
index 0000000..c181828
--- /dev/null
+++ b/lzma/common/vli_decoder.c
@@ -0,0 +1,86 @@
+///////////////////////////////////////////////////////////////////////////////
+//
+/// \file       vli_decoder.c
+/// \brief      Decodes variable-length integers
+//
+//  Author:     Lasse Collin
+//
+//  This file has been put into the public domain.
+//  You can do whatever you want with this file.
+//
+///////////////////////////////////////////////////////////////////////////////
+
+#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 istead 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;
+}