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Replaced the range decoder optimization that used arithmetic

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right shift with as fast version that doesn't need
arithmetic right shift. Removed the related check from
configure.ac.
This commit is contained in:
Lasse Collin 2008-03-24 16:38:40 +02:00
parent ad999efd27
commit 641998c3e1
3 changed files with 16 additions and 74 deletions
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1
configure.ac
View File

@ -407,7 +407,6 @@ AC_CHECK_HEADERS([assert.h errno.h byteswap.h sys/param.h sys/sysctl.h],
AC_C_INLINE
AC_C_RESTRICT
AX_C_ARITHMETIC_RSHIFT
AC_HEADER_STDBOOL

36
m4/ax_c_arithmetic_rshift.m4
View File

@ -1,36 +0,0 @@
##### http://autoconf-archive.cryp.to/ax_c_arithmetic_rshift.html
#
# SYNOPSIS
#
# AX_C_ARITHMETIC_RSHIFT
#
# DESCRIPTION
#
# Checks if the right shift operation is arithmetic.
#
# This macro uses compile-time detection and so is cross-compile
# ready.
#
# LAST MODIFICATION
#
# 2006-12-12
#
# COPYLEFT
#
# Copyright (c) 2006 YAMAMOTO Kengo <yamaken AT bp.iij4u.or.jp>
#
# Copying and distribution of this file, with or without
# modification, are permitted in any medium without royalty provided
# the copyright notice and this notice are preserved.
AC_DEFUN([AX_C_ARITHMETIC_RSHIFT], [
AC_CACHE_CHECK([whether right shift operation is arithmetic],
[ax_cv_c_arithmetic_rshift],
[AC_COMPILE_IFELSE([[int dummy[((-1 >> 1) < 0) ? 1 : -1];]],
[ax_cv_c_arithmetic_rshift=yes],
[ax_cv_c_arithmetic_rshift=no])])
if test "x$ax_cv_c_arithmetic_rshift" = xyes; then
AC_DEFINE([HAVE_ARITHMETIC_RSHIFT], [1],
[Define to 1 if the right shift operation is arithmetic.])
fi
])

39
src/liblzma/rangecoder/range_decoder.h
View File

@ -121,26 +121,15 @@ do { \
} while (0)
#ifdef HAVE_ARITHMETIC_RSHIFT
# define rc_decode_direct(dest, count) \
do { \
#define rc_decode_direct(dest, count) \
do { \
rc_normalize(); \
rc.range >>= 1; \
rc.code -= rc.range; \
rc_bound = (uint32_t)((int32_t)(rc.code) >> 31); \
dest = (dest << 1) + (rc_bound + 1); \
rc_bound = UINT32_C(0) - (rc.code >> 31); \
rc.code += rc.range & rc_bound; \
} while (--count > 0)
#else
# define rc_decode_direct(dest, count) \
do { \
rc_normalize(); \
rc.range >>= 1; \
rc_bound = (rc.code - rc.range) >> 31; \
rc.code -= rc.range & (rc_bound - 1); \
dest = ((dest) << 1) | (1 - rc_bound);\
} while (--count > 0)
#endif
dest = (dest << 1) + (rc_bound + 1); \
} while (--count > 0)
// Dummy versions don't update prob or dest.
@ -155,23 +144,13 @@ do { \
} while (0)
#ifdef HAVE_ARITHMETIC_RSHIFT
# define rc_decode_direct_dummy(count) \
do { \
#define rc_decode_direct_dummy(count) \
do { \
rc_normalize(); \
rc.range >>= 1; \
rc.code -= rc.range; \
rc.code += rc.range & ((uint32_t)((int32_t)(rc.code) >> 31)); \
} while (--count > 0)
#else
# define rc_decode_direct_dummy(count) \
do { \
rc_normalize(); \
rc.range >>= 1; \
rc_bound = (rc.code - rc.range) >> 31; \
rc.code -= rc.range & (rc_bound - 1); \
} while (--count > 0)
#endif
rc.code += rc.range & (UINT32_C(0) - (rc.code >> 31)); \
} while (--count > 0)
///////////////////////