text: ///////////////////////////////////////////////////////////////////////////////
  //
  /// \file       block_decoder.c
  /// \brief      Decodes .xz Blocks
  //
  //  Author:     Lasse Collin
  //
  //  This file has been put into the public domain.
  //  You can do whatever you want with this file.
  //
  ///////////////////////////////////////////////////////////////////////////////
  
  #include "block_decoder.h"
  #include "filter_decoder.h"
  #include "check.h"
  
  
  struct lzma_coder_s {
  	enum {
  		SEQ_CODE,
  		SEQ_PADDING,
  		SEQ_CHECK,
  	} sequence;
  
  	/// The filters in the chain; initialized with lzma_raw_decoder_init().
  	lzma_next_coder next;
  
  	/// Decoding options; we also write Compressed Size and Uncompressed
  	/// Size back to this structure when the decoding has been finished.
  	lzma_block *block;
  
  	/// Compressed Size calculated while decoding
  	lzma_vli compressed_size;
  
  	/// Uncompressed Size calculated while decoding
  	lzma_vli uncompressed_size;
  
  	/// Maximum allowed Compressed Size; this takes into account the
  	/// size of the Block Header and Check fields when Compressed Size
  	/// is unknown.
  	lzma_vli compressed_limit;
  
  	/// Position when reading the Check field
  	size_t check_pos;
  
  	/// Check of the uncompressed data
  	lzma_check_state check;
  };
  
  
  static inline bool
  update_size(lzma_vli *size, lzma_vli add, lzma_vli limit)
  {
  	if (limit > LZMA_VLI_MAX)
  		limit = LZMA_VLI_MAX;
  
  	if (limit < *size || limit - *size < add)
  		return true;
  
  	*size += add;
  
  	return false;
  }
  
  
  static inline bool
  is_size_valid(lzma_vli size, lzma_vli reference)
  {
  	return reference == LZMA_VLI_UNKNOWN || reference == size;
  }
  
  
  static lzma_ret
  block_decode(lzma_coder *coder, lzma_allocator *allocator,
  		const uint8_t *LZMA_RESTRICT in, size_t *LZMA_RESTRICT in_pos,
  		size_t in_size, uint8_t *LZMA_RESTRICT out,
  		size_t *LZMA_RESTRICT out_pos, size_t out_size, lzma_action action)
  {
  	switch (coder->sequence) {
  	case SEQ_CODE: {
  		const size_t in_start = *in_pos;
  		const size_t out_start = *out_pos;
  
  		const lzma_ret ret = coder->next.code(coder->next.coder,
  				allocator, in, in_pos, in_size,
  				out, out_pos, out_size, action);
  
  		const size_t in_used = *in_pos - in_start;
  		const size_t out_used = *out_pos - out_start;
  
  		// NOTE: We compare to compressed_limit here, which prevents
  		// the total size of the Block growing past LZMA_VLI_MAX.
  		if (update_size(&coder->compressed_size, in_used,
  					coder->compressed_limit)
  				|| update_size(&coder->uncompressed_size,
  					out_used,
  					coder->block->uncompressed_size))
  			return LZMA_DATA_ERROR;
  
  		lzma_check_update(&coder->check, coder->block->check,
  				out + out_start, out_used);
  
  		if (ret != LZMA_STREAM_END)
  			return ret;
  
  		// Compressed and Uncompressed Sizes are now at their final
  		// values. Verify that they match the values given to us.
  		if (!is_size_valid(coder->compressed_size,
  					coder->block->compressed_size)
  				|| !is_size_valid(coder->uncompressed_size,
  					coder->block->uncompressed_size))
  			return LZMA_DATA_ERROR;
  
  		// Copy the values into coder->block. The caller
  		// may use this information to construct Index.
  		coder->block->compressed_size = coder->compressed_size;
  		coder->block->uncompressed_size = coder->uncompressed_size;
  
  		coder->sequence = SEQ_PADDING;
  	}
  
  	// Fall through
  
  	case SEQ_PADDING:
  		// Compressed Data is padded to a multiple of four bytes.
  		while (coder->compressed_size & 3) {
  			if (*in_pos >= in_size)
  				return LZMA_OK;
  
  			// We use compressed_size here just get the Padding
  			// right. The actual Compressed Size was stored to
  			// coder->block already, and won't be modified by
  			// us anymore.
  			++coder->compressed_size;
  
  			if (in[(*in_pos)++] != 0x00)
  				return LZMA_DATA_ERROR;
  		}
  
  		if (coder->block->check == LZMA_CHECK_NONE)
  			return LZMA_STREAM_END;
  
  		lzma_check_finish(&coder->check, coder->block->check);
  		coder->sequence = SEQ_CHECK;
  
  	// Fall through
  
  	case SEQ_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;
  
  		// 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;
  
  		return LZMA_STREAM_END;
  	}
  	}
  
  	return LZMA_PROG_ERROR;
  }
  
  
  static void
  block_decoder_end(lzma_coder *coder, lzma_allocator *allocator)
  {
  	lzma_next_end(&coder->next, allocator);
  	lzma_free(coder, allocator);
  	return;
  }
  
  
  extern lzma_ret
  lzma_block_decoder_init(lzma_next_coder *next, lzma_allocator *allocator,
  		lzma_block *block)
  {
  	lzma_next_coder_init(&lzma_block_decoder_init, next, allocator);
  
  	// Validate the options. lzma_block_unpadded_size() does that for us
  	// except for Uncompressed Size and filters. Filters are validated
  	// by the raw decoder.
  	if (lzma_block_unpadded_size(block) == 0
  			|| !lzma_vli_is_valid(block->uncompressed_size))
  		return LZMA_PROG_ERROR;
  
  	// Allocate and initialize *next->coder if needed.
  	if (next->coder == NULL) {
  		next->coder = lzma_alloc(sizeof(lzma_coder), allocator);
  		if (next->coder == NULL)
  			return LZMA_MEM_ERROR;
  
  		next->code = &block_decode;
  		next->end = &block_decoder_end;
  		next->coder->next = LZMA_NEXT_CODER_INIT;
  	}
  
  	// Basic initializations
  	next->coder->sequence = SEQ_CODE;
  	next->coder->block = block;
  	next->coder->compressed_size = 0;
  	next->coder->uncompressed_size = 0;
  
  	// If Compressed Size is not known, we calculate the maximum allowed
  	// value so that encoded size of the Block (including Block Padding)
  	// is still a valid VLI and a multiple of four.
  	next->coder->compressed_limit
  			= block->compressed_size == LZMA_VLI_UNKNOWN
  				? (LZMA_VLI_MAX & ~LZMA_VLI_C(3))
  					- block->header_size
  					- lzma_check_size(block->check)
  				: block->compressed_size;
  
  	// Initialize the check. It's caller's problem if the Check ID is not
  	// supported, and the Block decoder cannot verify the Check field.
  	// Caller can test lzma_check_is_supported(block->check).
  	next->coder->check_pos = 0;
  	lzma_check_init(&next->coder->check, block->check);
  
  	// Initialize the filter chain.
  	return lzma_raw_decoder_init(&next->coder->next, allocator,
  			block->filters);
  }
  
  
  extern LZMA_API(lzma_ret)
  lzma_block_decoder(lzma_stream *strm, lzma_block *block)
  {
  	lzma_next_strm_init1(lzma_block_decoder_init, strm, block);
  
  	strm->internal->supported_actions[LZMA_RUN] = true;
  	strm->internal->supported_actions[LZMA_FINISH] = true;
  
  	return LZMA_OK;
  }
  