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1c4cebb84b
Add calloc-clear-memory.h to clear memory size up to 36 bytes (72 bytes on 64-bit targets) for calloc. Use repeated stores with 1 branch, instead of up to 3 branches. On x86-64, it is faster than memset since calling memset needs 1 indirect branch, 1 broadcast, and up to 4 branches. Signed-off-by: H.J. Lu <hjl.tools@gmail.com> Reviewed-by: Wilco Dijkstra <Wilco.Dijkstra@arm.com>
50 lines
1.6 KiB
C
50 lines
1.6 KiB
C
/* Clear a block of memory for calloc. Generic version.
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Copyright (C) 2024 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C 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 2.1 of the License, or (at your option) any later version.
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The GNU C 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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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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static __always_inline void *
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clear_memory (INTERNAL_SIZE_T *d, unsigned long clearsize)
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{
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/* Unroll clear memory size up to 9 * INTERNAL_SIZE_T bytes. We know
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that contents have an odd number of INTERNAL_SIZE_T-sized words;
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minimally 3 words. */
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unsigned long nclears = clearsize / sizeof (INTERNAL_SIZE_T);
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if (nclears > 9)
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return memset (d, 0, clearsize);
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/* NB: The VRP pass in GCC 14.2 will optimize it out. */
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if (nclears < 3)
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__builtin_unreachable ();
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/* Use repeated stores with 1 branch, instead of up to 3. */
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*(d + 0) = 0;
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*(d + 1) = 0;
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*(d + 2) = 0;
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*(d + nclears - 2) = 0;
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*(d + nclears - 2 + 1) = 0;
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if (nclears > 5)
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{
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*(d + 3) = 0;
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*(d + 3 + 1) = 0;
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*(d + nclears - 4) = 0;
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*(d + nclears - 4 + 1) = 0;
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}
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return d;
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}
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