1 files changed, 74 insertions, 0 deletions
diff --git a/src/liblzma/common/chunk_size.c b/src/liblzma/common/chunk_size.c
new file mode 100644
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+++ b/src/liblzma/common/chunk_size.c
@@ -0,0 +1,74 @@
+///////////////////////////////////////////////////////////////////////////////
+//
+/// \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;
+}