Revised the Delta filter implementation. The initialization

function is still shared between encoder and decoder, but the
actual coding is in separate files for encoder and decoder.

There are now separate functions for the actual delta
calculation depending on if Delta is the last filter in the
chain or not. If it is the last, the new code copies the
data from input to output buffer and does the delta
calculation at the same time. The old code first copied the
data, then did the delta in the target buffer, which required
reading through the data twice.

Support for LZMA_SYNC_FLUSH was added to the Delta encoder.
This doesn't change anything in the file format.

1 files changed, 102 insertions, 0 deletions

diff --git a/src/liblzma/common/delta_decoder.c b/src/liblzma/common/delta_decoder.c
new file mode 100644
index 00000000..af2b840d
--- /dev/null
+++ b/src/liblzma/common/delta_decoder.c
@@ -0,0 +1,102 @@
+///////////////////////////////////////////////////////////////////////////////
+//
+/// \file       delta_decoder.c
+/// \brief      Delta filter decoder
+//
+//  Copyright (C) 2007, 2008 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 "delta_decoder.h"
+#include "delta_common.h"
+
+
+/// Copies and decodes the data at the same time. This is used when Delta
+/// is the last filter in the chain.
+static void
+copy_and_decode(lzma_coder *coder,
+		const uint8_t *restrict in, uint8_t *restrict out, size_t size)
+{
+	const size_t distance = coder->distance;
+
+	for (size_t i = 0; i < size; ++i) {
+		out[i] = in[i] + coder->history[
+				(distance + coder->pos) & 0xFF];
+		coder->history[coder->pos-- & 0xFF] = out[i];
+	}
+}
+
+
+/// Decodes the data in place. This is used when we are not the last filter
+/// in the chain.
+static void
+decode_in_place(lzma_coder *coder, uint8_t *buffer, size_t size)
+{
+	const size_t distance = coder->distance;
+
+	for (size_t i = 0; i < size; ++i) {
+		buffer[i] += coder->history[(distance + coder->pos) & 0xFF];
+		coder->history[coder->pos-- & 0xFF] = buffer[i];
+	}
+}
+
+
+
+static lzma_ret
+delta_decode(lzma_coder *coder, lzma_allocator *allocator,
+		const uint8_t *restrict in, size_t *restrict in_pos,
+		size_t in_size, uint8_t *restrict out,
+		size_t *restrict out_pos, size_t out_size, lzma_action action)
+{
+	lzma_ret ret;
+
+	if (coder->next.code == NULL) {
+		// Limit in_size so that we don't copy too much.
+		if ((lzma_vli)(in_size - *in_pos) > coder->uncompressed_size)
+			in_size = *in_pos + (size_t)(coder->uncompressed_size);
+
+		const size_t in_avail = in_size - *in_pos;
+		const size_t out_avail = out_size - *out_pos;
+		const size_t size = MIN(in_avail, out_avail);
+
+		copy_and_decode(coder, in + *in_pos, out + *out_pos, size);
+
+		*in_pos += size;
+		*out_pos += size;
+
+		assert(coder->uncompressed_size <= LZMA_VLI_VALUE_MAX);
+		coder->uncompressed_size -= size;
+
+		ret = coder->uncompressed_size == 0
+				? LZMA_STREAM_END : LZMA_OK;
+
+	} else {
+		const size_t out_start = *out_pos;
+
+		ret = coder->next.code(coder->next.coder, allocator,
+				in, in_pos, in_size, out, out_pos, out_size,
+				action);
+
+		decode_in_place(coder, out + out_start, *out_pos - out_start);
+	}
+
+	return ret;
+}
+
+
+extern lzma_ret
+lzma_delta_decoder_init(lzma_next_coder *next, lzma_allocator *allocator,
+		const lzma_filter_info *filters)
+{
+	return lzma_delta_coder_init(next, allocator, filters, &delta_decode);
+}