zyfeier commented on code in PR #8042: URL: https://github.com/apache/nuttx/pull/8042#discussion_r1064315965
########## libs/libc/machine/arm64/gnu/arch_strnlen.S: ########## @@ -0,0 +1,188 @@ +/**************************************************************************** + * libs/libc/machine/arm64/gnu/arch_strnlen.S + * + * Copyright (c) 2013, Linaro Limited + * All rights reserved. + * + * Redistribution and use in source and binary forms, with or without + * modification, are permitted provided that the following conditions + * are met: + * + * * Redistributions of source code must retain the above copyright + * notice, this list of conditions and the following disclaimer. + * + * * Redistributions in binary form must reproduce the above copyright + * notice, this list of conditions and the following disclaimer in the + * documentation and/or other materials provided with the distribution. + * + * * Neither the name of the Linaro nor the names of its + * contributors may be used to endorse or promote products derived + * from this software without specific prior written permission. + * + * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS + * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT + * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR + * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT + * HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, + * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT + * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, + * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY + * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT + * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE + * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. + * + ****************************************************************************/ + +/* 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 + + .macro def_fn f p2align=0 + .text + .p2align \p2align + .global \f + .type \f, %function +\f: + .endm + +#define REP8_01 0x0101010101010101 +#define REP8_7f 0x7f7f7f7f7f7f7f7f +#define REP8_80 0x8080808080808080 + + .text + .p2align 6 +.Lstart: + /* Pre-pad to ensure critical loop begins an icache line. */ + .rep 7 + nop + .endr + /* Put this code here to avoid wasting more space with pre-padding. */ +.Lhit_limit: + mov len, limit + ret + +def_fn strnlen + cbz limit, .Lhit_limit + mov zeroones, #REP8_01 + bic src, srcin, #15 + ands tmp1, srcin, #15 + b.ne .Lmisaligned + /* 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. */ +.Lloop: + ldp data1, data2, [src], #16 +.Lrealigned: + 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 .Lloop + /* End of critical section -- keep to one 64Byte cache line. */ + + orr tmp1, has_nul1, has_nul2 + cbz tmp1, .Lhit_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, .Lnul_in_data2 +#ifdef __AARCH64EB__ + mov data2, data1 +#endif + sub len, len, #8 + mov has_nul2, has_nul1 +.Lnul_in_data2: +#ifdef __AARCH64EB__ Review Comment: It's gcc predefined macro. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected]
