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authorLasse Collin <lasse.collin@tukaani.org>2007-12-09 00:42:33 +0200
committerLasse Collin <lasse.collin@tukaani.org>2007-12-09 00:42:33 +0200
commit5d018dc03549c1ee4958364712fb0c94e1bf2741 (patch)
tree1b211911fb33fddb3f04b77f99e81df23623ffc4 /src/liblzma/common/chunk_size.c
downloadxz-5d018dc03549c1ee4958364712fb0c94e1bf2741.tar.xz
Imported to git.
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+///////////////////////////////////////////////////////////////////////////////
+//
+/// \file chunk_size.c
+/// \brief Finds out the minimal reasonable chunk size for a filter chain
+//
+// Copyright (C) 2007 Lasse Collin
+//
+// This library is free software; you can redistribute it and/or
+// modify it under the terms of the GNU Lesser General Public
+// License as published by the Free Software Foundation; either
+// version 2.1 of the License, or (at your option) any later version.
+//
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+// Lesser General Public License for more details.
+//
+///////////////////////////////////////////////////////////////////////////////
+
+#include "common.h"
+
+
+/**
+ * \brief Finds out the minimal reasonable chunk size for a filter chain
+ *
+ * This function helps determining the Uncompressed Sizes of the Blocks when
+ * doing multi-threaded encoding.
+ *
+ * When compressing a large file on a system having multiple CPUs or CPU
+ * cores, the file can be splitted in smaller chunks, that are compressed
+ * independently into separate Blocks in the same .lzma Stream.
+ *
+ * \return Minimum reasonable Uncompressed Size of a Block. The
+ * recommended minimum Uncompressed Size is between this value
+ * and the value times two.
+
+ Zero if the Uncompressed Sizes of Blocks don't matter
+ */
+extern LZMA_API size_t
+lzma_chunk_size(const lzma_options_filter *filters)
+{
+ while (filters->id != LZMA_VLI_VALUE_UNKNOWN) {
+ switch (filters->id) {
+ // TODO LZMA_FILTER_SPARSE
+
+ case LZMA_FILTER_COPY:
+ case LZMA_FILTER_SUBBLOCK:
+ case LZMA_FILTER_X86:
+ case LZMA_FILTER_POWERPC:
+ case LZMA_FILTER_IA64:
+ case LZMA_FILTER_ARM:
+ case LZMA_FILTER_ARMTHUMB:
+ case LZMA_FILTER_SPARC:
+ // These are very fast, thus there is no point in
+ // splitting the data in smaller blocks.
+ break;
+
+ case LZMA_FILTER_LZMA:
+ // The block sizes of the possible next filters in
+ // the chain are irrelevant after the LZMA filter.
+ return ((lzma_options_lzma *)(filters->options))
+ ->dictionary_size;
+
+ default:
+ // Unknown filters
+ return 0;
+ }
+
+ ++filters;
+ }
+
+ // Indicate that splitting would be useless.
+ return SIZE_MAX;
+}