3 files changed, 20 insertions, 22 deletions

diff --git a/src/liblzma/common/filter_encoder.c b/src/liblzma/common/filter_encoder.c
index 46fe8af1..0699bcee 100644
--- a/src/liblzma/common/filter_encoder.c
+++ b/src/liblzma/common/filter_encoder.c
@@ -33,7 +33,8 @@ typedef struct {
 	/// Calculates the recommended Uncompressed Size for .xz Blocks to
 	/// which the input data can be split to make multithreaded
 	/// encoding possible. If this is NULL, it is assumed that
-	/// the encoder is fast enough with single thread.
+	/// the encoder is fast enough with single thread. If the options
+	/// are invalid, UINT64_MAX is returned.
 	uint64_t (*block_size)(const void *options);
 
 	/// Tells the size of the Filter Properties field. If options are
@@ -248,26 +249,29 @@ lzma_raw_encoder_memusage(const lzma_filter *filters)
 }
 
 
-extern uint64_t
+extern LZMA_API(uint64_t)
 lzma_mt_block_size(const lzma_filter *filters)
 {
+	if (filters == NULL)
+		return UINT64_MAX;
+
 	uint64_t max = 0;
 
 	for (size_t i = 0; filters[i].id != LZMA_VLI_UNKNOWN; ++i) {
 		const lzma_filter_encoder *const fe
 				= encoder_find(filters[i].id);
+		if (fe == NULL)
+			return UINT64_MAX;
+
 		if (fe->block_size != NULL) {
 			const uint64_t size
 					= fe->block_size(filters[i].options);
-			if (size == 0)
-				return 0;
-
 			if (size > max)
 				max = size;
 		}
 	}
 
-	return max;
+	return max == 0 ? UINT64_MAX : max;
 }
 
 
diff --git a/src/liblzma/common/filter_encoder.h b/src/liblzma/common/filter_encoder.h
index f1d5683f..da92be8b 100644
--- a/src/liblzma/common/filter_encoder.h
+++ b/src/liblzma/common/filter_encoder.h
@@ -1,6 +1,6 @@
 ///////////////////////////////////////////////////////////////////////////////
 //
-/// \file       filter_encoder.c
+/// \file       filter_encoder.h
 /// \brief      Filter ID mapping to filter-specific functions
 //
 //  Author:     Lasse Collin
@@ -16,10 +16,6 @@
 #include "common.h"
 
 
-// FIXME: Might become a part of the public API.
-extern uint64_t lzma_mt_block_size(const lzma_filter *filters);
-
-
 extern lzma_ret lzma_raw_encoder_init(
 		lzma_next_coder *next, const lzma_allocator *allocator,
 		const lzma_filter *filters);
diff --git a/src/liblzma/common/stream_encoder_mt.c b/src/liblzma/common/stream_encoder_mt.c
index 5990742b..703b794e 100644
--- a/src/liblzma/common/stream_encoder_mt.c
+++ b/src/liblzma/common/stream_encoder_mt.c
@@ -979,20 +979,18 @@ get_options(const lzma_mt *options, lzma_options_easy *opt_easy,
 		*filters = opt_easy->filters;
 	}
 
-	// Block size
-	if (options->block_size > 0) {
-		if (options->block_size > BLOCK_SIZE_MAX)
-			return LZMA_OPTIONS_ERROR;
-
+	// If the Block size is not set, determine it from the filter chain.
+	if (options->block_size > 0)
 		*block_size = options->block_size;
-	} else {
-		// Determine the Block size from the filter chain.
+	else
 		*block_size = lzma_mt_block_size(*filters);
-		if (*block_size == 0)
-			return LZMA_OPTIONS_ERROR;
 
-		assert(*block_size <= BLOCK_SIZE_MAX);
-	}
+	// UINT64_MAX > BLOCK_SIZE_MAX, so the second condition
+	// should be optimized out by any reasonable compiler.
+	// The second condition should be there in the unlikely event that
+	// the macros change and UINT64_MAX < BLOCK_SIZE_MAX.
+	if (*block_size > BLOCK_SIZE_MAX || *block_size == UINT64_MAX)
+		return LZMA_OPTIONS_ERROR;
 
 	// Calculate the maximum amount output that a single output buffer
 	// may need to hold. This is the same as the maximum total size of