Make the raw value of the Check field available to applications

via lzma_block structure.

This changes ABI but not doesn't break API.

src/liblzma/api/lzma/block.h

@@ -207,6 +207,23 @@ typedef struct {
 	 */
 	lzma_filter *filters;
 
+	/**
+	 * \brief       Raw value stored in the Check field
+	 *
+	 * After successful coding, the first lzma_check_size(check) bytes
+	 * of this array contain the raw value stored in the Check field.
+	 *
+	 * Note that CRC32 and CRC64 are stored in little endian byte order.
+	 * Take it into account if you display the Check values to the user.
+	 *
+	 * Written by:
+	 *  - lzma_block_encoder()
+	 *  - lzma_block_decoder()
+	 *  - lzma_block_buffer_encode()
+	 *  - lzma_block_buffer_decode()
+	 */
+	uint8_t raw_check[64];
+
 	/*
 	 * Reserved space to allow possible future extensions without
 	 * breaking the ABI. You should not touch these, because the names

src/liblzma/common/block_buffer_encoder.c

@@ -290,6 +290,7 @@ lzma_block_buffer_encode(lzma_block *block, lzma_allocator *allocator,
 		lzma_check_update(&check, block->check, in, in_size);
 		lzma_check_finish(&check, block->check);
 
+		memcpy(block->raw_check, check.buffer.u8, check_size);
 		memcpy(out + *out_pos, check.buffer.u8, check_size);
 		*out_pos += check_size;
 	}

src/liblzma/common/block_decoder.c

@@ -146,26 +146,22 @@ block_decode(lzma_coder *coder, lzma_allocator *allocator,
 	// Fall through
 
 	case SEQ_CHECK: {
-		const bool chksup = lzma_check_is_supported(
-				coder->block->check);
+		const size_t check_size = lzma_check_size(coder->block->check);
+		lzma_bufcpy(in, in_pos, in_size, coder->block->raw_check,
+				&coder->check_pos, check_size);
+		if (coder->check_pos < check_size)
+			return LZMA_OK;
 
-		while (*in_pos < in_size) {
-			// coder->check.buffer[] may be uninitialized when
-			// the Check ID is not supported.
-			if (chksup && coder->check.buffer.u8[coder->check_pos]
-					!= in[*in_pos]) {
-				++*in_pos;
-				return LZMA_DATA_ERROR;
-			}
+		// Validate the Check only if we support it.
+		// coder->check.buffer may be uninitialized
+		// when the Check ID is not supported.
+		if (lzma_check_is_supported(coder->block->check)
+				&& memcmp(coder->block->raw_check,
+					coder->check.buffer.u8,
+					check_size) != 0)
+			return LZMA_DATA_ERROR;
 
-			++*in_pos;
-
-			if (++coder->check_pos == lzma_check_size(
-					coder->block->check))
-				return LZMA_STREAM_END;
-		}
-
-		return LZMA_OK;
+		return LZMA_STREAM_END;
 	}
 	}
 

src/liblzma/common/block_encoder.c

@@ -117,18 +117,15 @@ block_encode(lzma_coder *coder, lzma_allocator *allocator,
 	// Fall through
 
 	case SEQ_CHECK: {
-		const uint32_t check_size
-				= lzma_check_size(coder->block->check);
+		const size_t check_size = lzma_check_size(coder->block->check);
+		lzma_bufcpy(coder->check.buffer.u8, &coder->pos, check_size,
+				out, out_pos, out_size);
+		if (coder->pos < check_size)
+			return LZMA_OK;
 
-		while (*out_pos < out_size) {
-			out[*out_pos] = coder->check.buffer.u8[coder->pos];
-			++*out_pos;
-
-			if (++coder->pos == check_size)
-				return LZMA_STREAM_END;
-		}
-
-		return LZMA_OK;
+		memcpy(coder->block->raw_check, coder->check.buffer.u8,
+				check_size);
+		return LZMA_STREAM_END;
 	}
 	}