| /* Copyright (C) 2012-2014 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 |
| */ |
| |
| /* Arguments and results. */ |
| #define srcin x0 |
| #define len x0 |
| |
| /* Locals and temporaries. */ |
| #define src x1 |
| #define data1 x2 |
| #define data2 x3 |
| #define data2a x4 |
| #define has_nul1 x5 |
| #define has_nul2 x6 |
| #define tmp1 x7 |
| #define tmp2 x8 |
| #define tmp3 x9 |
| #define tmp4 x10 |
| #define zeroones x11 |
| #define pos x12 |
| |
| #define REP8_01 0x0101010101010101 |
| #define REP8_7f 0x7f7f7f7f7f7f7f7f |
| #define REP8_80 0x8080808080808080 |
| |
| /* Start of critial section -- keep to one 64Byte cache line. */ |
| ENTRY_ALIGN (strlen, 6) |
| mov zeroones, #REP8_01 |
| bic src, srcin, #15 |
| ands tmp1, srcin, #15 |
| b.ne L(misaligned) |
| /* 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. */ |
| /* The inner loop deals with two Dwords at a time. This has a |
| slightly higher start-up cost, but we should win quite quickly, |
| especially on cores with a high number of issue slots per |
| cycle, as we get much better parallelism out of the operations. */ |
| L(loop): |
| ldp data1, data2, [src], #16 |
| L(realigned): |
| sub tmp1, data1, zeroones |
| orr tmp2, data1, #REP8_7f |
| sub tmp3, data2, zeroones |
| orr tmp4, data2, #REP8_7f |
| bic has_nul1, tmp1, tmp2 |
| bics has_nul2, tmp3, tmp4 |
| ccmp has_nul1, #0, #0, eq /* NZCV = 0000 */ |
| b.eq L(loop) |
| /* End of critical section -- keep to one 64Byte cache line. */ |
| |
| sub len, src, srcin |
| cbz has_nul1, L(nul_in_data2) |
| #ifdef __AARCH64EB__ |
| mov data2, data1 |
| #endif |
| sub len, len, #8 |
| mov has_nul2, has_nul1 |
| L(nul_in_data2): |
| #ifdef __AARCH64EB__ |
| /* For big-endian, carry propagation (if the final byte in the |
| string is 0x01) means we cannot use has_nul directly. The |
| easiest way to get the correct byte is to byte-swap the data |
| and calculate the syndrome a second time. */ |
| rev data2, data2 |
| sub tmp1, data2, zeroones |
| orr tmp2, data2, #REP8_7f |
| bic has_nul2, tmp1, tmp2 |
| #endif |
| sub len, len, #8 |
| rev has_nul2, has_nul2 |
| clz pos, has_nul2 |
| add len, len, pos, lsr #3 /* Bits to bytes. */ |
| RET |
| |
| L(misaligned): |
| cmp tmp1, #8 |
| neg tmp1, tmp1 |
| ldp data1, data2, [src], #16 |
| lsl tmp1, tmp1, #3 /* Bytes beyond alignment -> bits. */ |
| mov tmp2, #~0 |
| #ifdef __AARCH64EB__ |
| /* Big-endian. Early bytes are at MSB. */ |
| lsl tmp2, tmp2, tmp1 /* Shift (tmp1 & 63). */ |
| #else |
| /* Little-endian. Early bytes are at LSB. */ |
| lsr tmp2, tmp2, tmp1 /* Shift (tmp1 & 63). */ |
| #endif |
| orr data1, data1, tmp2 |
| orr data2a, data2, tmp2 |
| csinv data1, data1, xzr, le |
| csel data2, data2, data2a, le |
| b L(realigned) |
| END (strlen) |
| libc_hidden_builtin_def (strlen) |