mirror of
https://sourceware.org/git/glibc.git
synced 2024-11-22 04:50:07 +00:00
79 lines
2.9 KiB
C
79 lines
2.9 KiB
C
/* Macro for explicit loop unrolling.
|
|
Copyright (C) 2019-2024 Free Software Foundation, Inc.
|
|
This file is part of the GNU C Library.
|
|
|
|
The GNU C 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.
|
|
|
|
The GNU C 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.
|
|
|
|
You should have received a copy of the GNU Lesser General Public
|
|
License along with the GNU C Library; if not, see
|
|
<https://www.gnu.org/licenses/>. */
|
|
|
|
#ifndef _LOOP_UNROLL_H
|
|
#define _LOOP_UNROLL_H
|
|
|
|
/* Loop unroll macro to be used for explicit force loop unrolling with a
|
|
configurable number of iterations. The idea is to make the loop unrolling
|
|
independent of whether the compiler is able to unroll through specific
|
|
optimizations options (-funroll-loops or -funroll-all-loops).
|
|
|
|
For instance, to implement strcpy with SRC being the source input and
|
|
DEST the destination buffer, it is expected the macro to be used in this
|
|
way:
|
|
|
|
#define ITERATION(index) \
|
|
({ char c = *str++; *dest++ = c; c != '\0' })
|
|
|
|
while (1)
|
|
UNROLL_REPEAT (4, ITERATION)
|
|
|
|
The loop will be manually unrolled 4 times. Another option is to do
|
|
the index update after the tests:
|
|
|
|
#define ITERATION(index) \
|
|
({ char c = *(str + index); *(dest + index) = c; c != '\0' })
|
|
#define UPDATE(n) \
|
|
str += n; dst += n
|
|
|
|
while (1)
|
|
UNROLL_REPEAT_UPDATE (4, ITERATION, UPDATE)
|
|
|
|
The loop will be manually unrolled 4 times and the SRC and DEST pointers
|
|
will be updated only after the last iteration.
|
|
|
|
Currently, both macros unroll the loop 8 times at maximum. */
|
|
|
|
#define UNROLL_REPEAT_1(X) if (!X(0)) break;
|
|
#define UNROLL_REPEAT_2(X) UNROLL_REPEAT_1 (X) if (!X (1)) break;
|
|
#define UNROLL_REPEAT_3(X) UNROLL_REPEAT_2 (X) if (!X (2)) break;
|
|
#define UNROLL_REPEAT_4(X) UNROLL_REPEAT_3 (X) if (!X (3)) break;
|
|
#define UNROLL_REPEAT_5(X) UNROLL_REPEAT_4 (X) if (!X (4)) break;
|
|
#define UNROLL_REPEAT_6(X) UNROLL_REPEAT_5 (X) if (!X (5)) break;
|
|
#define UNROLL_REPEAT_7(X) UNROLL_REPEAT_6 (X) if (!X (6)) break;
|
|
#define UNROLL_REPEAT_8(X) UNROLL_REPEAT_7 (X) if (!X (7)) break;
|
|
|
|
#define UNROLL_EXPAND(...) __VA_ARGS__
|
|
|
|
#define UNROLL_REPEAT__(N, X) UNROLL_EXPAND(UNROLL_REPEAT_ ## N) (X)
|
|
#define UNROLL_REPEAT_(N, X) UNROLL_REPEAT__ (N, X)
|
|
|
|
#define UNROLL_REPEAT(N, X) \
|
|
(void) ({ \
|
|
UNROLL_REPEAT_ (UNROLL_EXPAND(N), X); \
|
|
})
|
|
|
|
#define UNROLL_REPEAT_UPDATE(N, X, U) \
|
|
(void) ({ \
|
|
UNROLL_REPEAT_ (UNROLL_EXPAND(N), X); \
|
|
UPDATE (N); \
|
|
})
|
|
|
|
#endif
|