| /* strnlen - calculate the length of a string with limit. |
| |
| Copyright (C) 2013-2018 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 |
| #define limit x1 |
| |
| /* Locals and temporaries. */ |
| #define src x2 |
| #define data1 x3 |
| #define data2 x4 |
| #define data2a x5 |
| #define has_nul1 x6 |
| #define has_nul2 x7 |
| #define tmp1 x8 |
| #define tmp2 x9 |
| #define tmp3 x10 |
| #define tmp4 x11 |
| #define zeroones x12 |
| #define pos x13 |
| #define limit_wd x14 |
| |
| #define REP8_01 0x0101010101010101 |
| #define REP8_7f 0x7f7f7f7f7f7f7f7f |
| #define REP8_80 0x8080808080808080 |
| |
| ENTRY_ALIGN_AND_PAD (__strnlen, 6, 9) |
| DELOUSE (0) |
| DELOUSE (1) |
| DELOUSE (2) |
| cbz limit, L(hit_limit) |
| mov zeroones, #REP8_01 |
| bic src, srcin, #15 |
| ands tmp1, srcin, #15 |
| b.ne L(misaligned) |
| /* Calculate the number of full and partial words -1. */ |
| sub limit_wd, limit, #1 /* Limit != 0, so no underflow. */ |
| lsr limit_wd, limit_wd, #4 /* Convert to Qwords. */ |
| |
| /* 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. */ |
| |
| /* Start of critial section -- keep to one 64Byte cache line. */ |
| 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 |
| bic has_nul2, tmp3, tmp4 |
| subs limit_wd, limit_wd, #1 |
| orr tmp1, has_nul1, has_nul2 |
| ccmp tmp1, #0, #0, pl /* NZCV = 0000 */ |
| b.eq L(loop) |
| /* End of critical section -- keep to one 64Byte cache line. */ |
| |
| orr tmp1, has_nul1, has_nul2 |
| cbz tmp1, L(hit_limit) /* No null in final Qword. */ |
| |
| /* We know there's a null in the final Qword. The easiest thing |
| to do now is work out the length of the string and return |
| MIN (len, limit). */ |
| |
| 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. */ |
| cmp len, limit |
| csel len, len, limit, ls /* Return the lower value. */ |
| RET |
| |
| L(misaligned): |
| /* Deal with a partial first word. |
| We're doing two things in parallel here; |
| 1) Calculate the number of words (but avoiding overflow if |
| limit is near ULONG_MAX) - to do this we need to work out |
| limit + tmp1 - 1 as a 65-bit value before shifting it; |
| 2) Load and mask the initial data words - we force the bytes |
| before the ones we are interested in to 0xff - this ensures |
| early bytes will not hit any zero detection. */ |
| sub limit_wd, limit, #1 |
| neg tmp4, tmp1 |
| cmp tmp1, #8 |
| |
| and tmp3, limit_wd, #15 |
| lsr limit_wd, limit_wd, #4 |
| mov tmp2, #~0 |
| |
| ldp data1, data2, [src], #16 |
| lsl tmp4, tmp4, #3 /* Bytes beyond alignment -> bits. */ |
| add tmp3, tmp3, tmp1 |
| |
| #ifdef __AARCH64EB__ |
| /* Big-endian. Early bytes are at MSB. */ |
| lsl tmp2, tmp2, tmp4 /* Shift (tmp1 & 63). */ |
| #else |
| /* Little-endian. Early bytes are at LSB. */ |
| lsr tmp2, tmp2, tmp4 /* Shift (tmp1 & 63). */ |
| #endif |
| add limit_wd, limit_wd, tmp3, lsr #4 |
| |
| orr data1, data1, tmp2 |
| orr data2a, data2, tmp2 |
| |
| csinv data1, data1, xzr, le |
| csel data2, data2, data2a, le |
| b L(realigned) |
| |
| L(hit_limit): |
| mov len, limit |
| RET |
| END (__strnlen) |
| libc_hidden_def (__strnlen) |
| weak_alias (__strnlen, strnlen) |
| libc_hidden_def (strnlen) |