Revised the fastpos code. It now uses the slightly faster

table-based version from LZMA SDK 4.57. This should be
fast on most systems.

A simpler and smaller alternative version is also provided.
On some CPUs this can be even a little faster than the
default table-based version (see comments in fastpos.h),
but on most systems the table-based code is faster.

1 files changed, 63 insertions, 0 deletions

diff --git a/src/liblzma/lzma/fastpos_tablegen.c b/src/liblzma/lzma/fastpos_tablegen.c
new file mode 100644
index 00000000..90ab6c23
--- /dev/null
+++ b/src/liblzma/lzma/fastpos_tablegen.c
@@ -0,0 +1,63 @@
+///////////////////////////////////////////////////////////////////////////////
+//
+/// \file       fastpos_tablegen.c
+/// \brief      Generates the lzma_fastpos[] lookup table
+//
+//  Copyright (C) 1999-2007 Igor Pavlov
+//  Copyright (C) 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 <sys/types.h>
+#include <inttypes.h>
+#include <stdio.h>
+#include "fastpos.h"
+
+
+int
+main(void)
+{
+	uint8_t fastpos[1 << FASTPOS_BITS];
+
+	const uint8_t fast_slots = 2 * FASTPOS_BITS;
+	uint32_t c = 2;
+
+	fastpos[0] = 0;
+	fastpos[1] = 1;
+
+	for (uint8_t slot_fast = 2; slot_fast < fast_slots; ++slot_fast) {
+		const uint32_t k = 1 << ((slot_fast >> 1) - 1);
+		for (uint32_t j = 0; j < k; ++j, ++c)
+			fastpos[c] = slot_fast;
+	}
+
+	printf("/* This file has been automatically generated "
+			"by fastpos_tablegen.c. */\n\n"
+			"#include \"common.h\"\n"
+			"#include \"fastpos.h\"\n\n"
+			"const uint8_t lzma_fastpos[1 << FASTPOS_BITS] = {");
+
+	for (size_t i = 0; i < (1 << FASTPOS_BITS); ++i) {
+		if (i % 16 == 0)
+			printf("\n\t");
+
+		printf("%3u", (unsigned int)(fastpos[i]));
+
+		if (i != (1 << FASTPOS_BITS) - 1)
+			printf(",");
+	}
+
+	printf("\n};\n");
+
+	return 0;
+}