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2ba4fe417a
Instead of testing each bit when iterating a bitmask, we can use ffsl to skip over unset bits in single instruction. That way it will scale by the number of bits set, not the total number of bits. ffsl is a non-standard function which glibc only provides by defining GNUC_SOURCE. However if we are compiling with GCC we can avoid that mess and just use the equivalent builtin. When not compiling for GCC it will fall back to _cogl_util_ffs if the size of ints and longs are the same (which is the case on i686). Otherwise it fallbacks to a slow function implementation. Reviewed-by: Robert Bragg <robert@linux.intel.com>
103 lines
2.0 KiB
C
103 lines
2.0 KiB
C
/*
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* Cogl
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*
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* An object oriented GL/GLES Abstraction/Utility Layer
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*
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* Copyright (C) 2007,2008,2009,2010 Intel Corporation.
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*
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* This library is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2 of the License, or (at your option) any later version.
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*
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* This library is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with this library. If not, see <http://www.gnu.org/licenses/>.
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*
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*
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*/
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#ifdef HAVE_CONFIG_H
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#include "config.h"
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#endif
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#include "cogl-util.h"
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/*
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* cogl_util_next_p2:
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* @a: Value to get the next power of two
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*
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* Calculates the next power of two greater than or equal to @a.
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*
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* Return value: @a if @a is already a power of two, otherwise returns
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* the next nearest power of two.
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*/
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int
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_cogl_util_next_p2 (int a)
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{
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int rval = 1;
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while (rval < a)
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rval <<= 1;
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return rval;
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}
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unsigned int
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_cogl_util_one_at_a_time_mix (unsigned int hash)
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{
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hash += ( hash << 3 );
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hash ^= ( hash >> 11 );
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hash += ( hash << 15 );
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return hash;
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}
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/* The 'ffs' function is part of C99 so it isn't always available */
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#ifndef HAVE_FFS
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int
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_cogl_util_ffs (int num)
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{
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int i = 1;
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if (num == 0)
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return 0;
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while ((num & 1) == 0)
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{
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num >>= 1;
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i++;
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}
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return i;
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}
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#endif /* HAVE_FFS */
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/* The 'ffsl' is non-standard but when building with GCC we'll use its
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builtin instead */
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#ifndef COGL_UTIL_HAVE_BUILTIN_FFSL
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int
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_cogl_util_ffsl_wrapper (long int num)
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{
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int i = 1;
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if (num == 0)
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return 0;
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while ((num & 1) == 0)
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{
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num >>= 1;
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i++;
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}
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return i;
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}
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#endif /* COGL_UTIL_HAVE_BUILTIN_FFSL */
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