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Diffstat (limited to 'sysdeps/aarch64/strlen.S')
| -rw-r--r-- | sysdeps/aarch64/strlen.S | 220 |
1 files changed, 0 insertions, 220 deletions
diff --git a/sysdeps/aarch64/strlen.S b/sysdeps/aarch64/strlen.S deleted file mode 100644 index 4daf8b8500..0000000000 --- a/sysdeps/aarch64/strlen.S +++ /dev/null @@ -1,220 +0,0 @@ -/* Copyright (C) 2012-2017 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 - <http://www.gnu.org/licenses/>. */ - -#include <sysdep.h> - -/* Assumptions: - * - * ARMv8-a, AArch64, unaligned accesses, min page size 4k. - */ - -/* To test the page crossing code path more thoroughly, compile with - -DTEST_PAGE_CROSS - this will force all calls through the slower - entry path. This option is not intended for production use. */ - -/* Arguments and results. */ -#define srcin x0 -#define len x0 - -/* Locals and temporaries. */ -#define src x1 -#define data1 x2 -#define data2 x3 -#define has_nul1 x4 -#define has_nul2 x5 -#define tmp1 x4 -#define tmp2 x5 -#define tmp3 x6 -#define tmp4 x7 -#define zeroones x8 - - /* NUL detection works on the principle that (X - 1) & (~X) & 0x80 - (=> (X - 1) & ~(X | 0x7f)) is non-zero iff a byte is zero, and - can be done in parallel across the entire word. A faster check - (X - 1) & 0x80 is zero for non-NUL ASCII characters, but gives - false hits for characters 129..255. */ - -#define REP8_01 0x0101010101010101 -#define REP8_7f 0x7f7f7f7f7f7f7f7f -#define REP8_80 0x8080808080808080 - -#ifdef TEST_PAGE_CROSS -# define MIN_PAGE_SIZE 15 -#else -# define MIN_PAGE_SIZE 4096 -#endif - - /* Since strings are short on average, we check the first 16 bytes - of the string for a NUL character. In order to do an unaligned ldp - safely we have to do a page cross check first. If there is a NUL - byte we calculate the length from the 2 8-byte words using - conditional select to reduce branch mispredictions (it is unlikely - strlen will be repeatedly called on strings with the same length). - - If the string is longer than 16 bytes, we align src so don't need - further page cross checks, and process 32 bytes per iteration - using the fast NUL check. If we encounter non-ASCII characters, - fallback to a second loop using the full NUL check. - - If the page cross check fails, we read 16 bytes from an aligned - address, remove any characters before the string, and continue - in the main loop using aligned loads. Since strings crossing a - page in the first 16 bytes are rare (probability of - 16/MIN_PAGE_SIZE ~= 0.4%), this case does not need to be optimized. - - AArch64 systems have a minimum page size of 4k. We don't bother - checking for larger page sizes - the cost of setting up the correct - page size is just not worth the extra gain from a small reduction in - the cases taking the slow path. Note that we only care about - whether the first fetch, which may be misaligned, crosses a page - boundary. */ - -ENTRY_ALIGN (__strlen, 6) - DELOUSE (0) - DELOUSE (1) - and tmp1, srcin, MIN_PAGE_SIZE - 1 - mov zeroones, REP8_01 - cmp tmp1, MIN_PAGE_SIZE - 16 - b.gt L(page_cross) - ldp data1, data2, [srcin] -#ifdef __AARCH64EB__ - /* For big-endian, carry propagation (if the final byte in the - string is 0x01) means we cannot use has_nul1/2 directly. - Since we expect strings to be small and early-exit, - byte-swap the data now so has_null1/2 will be correct. */ - rev data1, data1 - rev data2, data2 -#endif - sub tmp1, data1, zeroones - orr tmp2, data1, REP8_7f - sub tmp3, data2, zeroones - orr tmp4, data2, REP8_7f - bics has_nul1, tmp1, tmp2 - bic has_nul2, tmp3, tmp4 - ccmp has_nul2, 0, 0, eq - beq L(main_loop_entry) - - /* Enter with C = has_nul1 == 0. */ - csel has_nul1, has_nul1, has_nul2, cc - mov len, 8 - rev has_nul1, has_nul1 - clz tmp1, has_nul1 - csel len, xzr, len, cc - add len, len, tmp1, lsr 3 - ret - - /* The inner loop processes 32 bytes per iteration and uses the fast - NUL check. If we encounter non-ASCII characters, use a second - loop with the accurate NUL check. */ - .p2align 4 -L(main_loop_entry): - bic src, srcin, 15 - sub src, src, 16 -L(main_loop): - ldp data1, data2, [src, 32]! -L(page_cross_entry): - sub tmp1, data1, zeroones - sub tmp3, data2, zeroones - orr tmp2, tmp1, tmp3 - tst tmp2, zeroones, lsl 7 - bne 1f - ldp data1, data2, [src, 16] - sub tmp1, data1, zeroones - sub tmp3, data2, zeroones - orr tmp2, tmp1, tmp3 - tst tmp2, zeroones, lsl 7 - beq L(main_loop) - add src, src, 16 -1: - /* The fast check failed, so do the slower, accurate NUL check. */ - orr tmp2, data1, REP8_7f - orr tmp4, data2, REP8_7f - bics has_nul1, tmp1, tmp2 - bic has_nul2, tmp3, tmp4 - ccmp has_nul2, 0, 0, eq - beq L(nonascii_loop) - - /* Enter with C = has_nul1 == 0. */ -L(tail): -#ifdef __AARCH64EB__ - /* For big-endian, carry propagation (if the final byte in the - string is 0x01) means we cannot use has_nul1/2 directly. The - easiest way to get the correct byte is to byte-swap the data - and calculate the syndrome a second time. */ - csel data1, data1, data2, cc - rev data1, data1 - sub tmp1, data1, zeroones - orr tmp2, data1, REP8_7f - bic has_nul1, tmp1, tmp2 -#else - csel has_nul1, has_nul1, has_nul2, cc -#endif - sub len, src, srcin - rev has_nul1, has_nul1 - add tmp2, len, 8 - clz tmp1, has_nul1 - csel len, len, tmp2, cc - add len, len, tmp1, lsr 3 - ret - -L(nonascii_loop): - ldp data1, data2, [src, 16]! - sub tmp1, data1, zeroones - orr tmp2, data1, REP8_7f - sub tmp3, data2, zeroones - orr tmp4, data2, REP8_7f - bics has_nul1, tmp1, tmp2 - bic has_nul2, tmp3, tmp4 - ccmp has_nul2, 0, 0, eq - bne L(tail) - ldp data1, data2, [src, 16]! - sub tmp1, data1, zeroones - orr tmp2, data1, REP8_7f - sub tmp3, data2, zeroones - orr tmp4, data2, REP8_7f - bics has_nul1, tmp1, tmp2 - bic has_nul2, tmp3, tmp4 - ccmp has_nul2, 0, 0, eq - beq L(nonascii_loop) - b L(tail) - - /* Load 16 bytes from [srcin & ~15] and force the bytes that precede - srcin to 0x7f, so we ignore any NUL bytes before the string. - Then continue in the aligned loop. */ -L(page_cross): - bic src, srcin, 15 - ldp data1, data2, [src] - lsl tmp1, srcin, 3 - mov tmp4, -1 -#ifdef __AARCH64EB__ - /* Big-endian. Early bytes are at MSB. */ - lsr tmp1, tmp4, tmp1 /* Shift (tmp1 & 63). */ -#else - /* Little-endian. Early bytes are at LSB. */ - lsl tmp1, tmp4, tmp1 /* Shift (tmp1 & 63). */ -#endif - orr tmp1, tmp1, REP8_80 - orn data1, data1, tmp1 - orn tmp2, data2, tmp1 - tst srcin, 8 - csel data1, data1, tmp4, eq - csel data2, data2, tmp2, eq - b L(page_cross_entry) -END (__strlen) -weak_alias (__strlen, strlen) -libc_hidden_builtin_def (strlen) |