Block encoder cleanups

1 files changed, 25 insertions, 0 deletions

diff --git a/src/liblzma/common/block_encoder.h b/src/liblzma/common/block_encoder.h
index d5b3ec0d..3113dab7 100644
--- a/src/liblzma/common/block_encoder.h
+++ b/src/liblzma/common/block_encoder.h
@@ -23,6 +23,31 @@
 #include "common.h"
 
 
+/// \brief      Biggest Compressed Size value that the Block encoder supports
+///
+/// The maximum size of a single Block is limited by the maximum size of
+/// a Stream, which in theory is 2^63 - 3 bytes (i.e. LZMA_VLI_MAX - 3).
+/// While the size is really big and no one should hit it in practice, we
+/// take it into account in some places anyway to catch some errors e.g. if
+/// application passes insanely big value to some function.
+///
+/// We could take into account the headers etc. to determine the exact
+/// maximum size of the Compressed Data field, but the complexity would give
+/// us nothing useful. Instead, limit the size of Compressed Data so that
+/// even with biggest possible Block Header and Check fields the total
+/// encoded size of the Block stays as a valid VLI. This doesn't guarantee
+/// that the size of the Stream doesn't grow too big, but that problem is
+/// taken care outside the Block handling code.
+///
+/// ~LZMA_VLI_C(3) is to guarantee that if we need padding at the end of
+/// the Compressed Data field, it will still stay in the proper limit.
+///
+/// This constant is in this file because it is needed in both
+/// block_encoder.c and block_buffer_encoder.c.
+#define COMPRESSED_SIZE_MAX ((LZMA_VLI_MAX - LZMA_BLOCK_HEADER_SIZE_MAX \
+		- LZMA_CHECK_SIZE_MAX) & ~LZMA_VLI_C(3))
+
+
 extern lzma_ret lzma_block_encoder_init(lzma_next_coder *next,
 		lzma_allocator *allocator, lzma_block *block);