From patchwork Wed Jan 7 10:47:39 2015 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Richard Earnshaw X-Patchwork-Id: 4542 Received: (qmail 16235 invoked by alias); 7 Jan 2015 10:47:47 -0000 Mailing-List: contact libc-alpha-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Unsubscribe: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: libc-alpha-owner@sourceware.org Delivered-To: mailing list libc-alpha@sourceware.org Received: (qmail 16219 invoked by uid 89); 7 Jan 2015 10:47:46 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-1.0 required=5.0 tests=AWL, BAYES_00, SPF_PASS autolearn=ham version=3.3.2 X-HELO: service87.mimecast.com Message-ID: <54AD0ECB.4070105@arm.com> Date: Wed, 07 Jan 2015 10:47:39 +0000 From: Richard Earnshaw User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.3.0 MIME-Version: 1.0 To: "libc-alpha@sourceware.org" Subject: [PATCH, AArch64] Add optimized strrchr X-MC-Unique: 115010710474104801 Similar to the strchr implementation, attached is an implementation of strrchr. Unlike the generic C version, this finds the last instance of a string without having to repeatedly call strchr. This gives notable performance improvements when there is more than one instance of the target character in the string (something the benchmarks never measure, by the way). OK? R. sysdeps/aarch64/strrchr.S: New file. diff --git a/sysdeps/aarch64/strrchr.S b/sysdeps/aarch64/strrchr.S new file mode 100644 index 0000000..b49e81d --- /dev/null +++ b/sysdeps/aarch64/strrchr.S @@ -0,0 +1,165 @@ +/* strrchr: find the last instance of a character in a string. + + Copyright (C) 2014-2015 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 + . */ + +#include + +/* Assumptions: + * + * ARMv8-a, AArch64 + * Neon Available. + */ + +/* Arguments and results. */ +#define srcin x0 +#define chrin w1 + +#define result x0 + +#define src x2 +#define tmp1 x3 +#define wtmp2 w4 +#define tmp3 x5 +#define src_match x6 +#define src_offset x7 +#define const_m1 x8 +#define tmp4 x9 +#define nul_match x10 +#define chr_match x11 + +#define vrepchr v0 +#define vdata1 v1 +#define vdata2 v2 +#define vhas_nul1 v3 +#define vhas_nul2 v4 +#define vhas_chr1 v5 +#define vhas_chr2 v6 +#define vrepmask_0 v7 +#define vrepmask_c v16 +#define vend1 v17 +#define vend2 v18 + +/* Core algorithm. + + For each 32-byte hunk we calculate a 64-bit syndrome value, with + two bits per byte (LSB is always in bits 0 and 1, for both big + and little-endian systems). For each tuple, bit 0 is set iff + the relevant byte matched the requested character; bit 1 is set + iff the relevant byte matched the NUL end of string (we trigger + off bit0 for the special case of looking for NUL). Since the bits + in the syndrome reflect exactly the order in which things occur + in the original string a count_trailing_zeros() operation will + identify exactly which byte is causing the termination, and why. */ + +ENTRY(strrchr) + cbz x1, L(null_search) + /* Magic constant 0x40100401 to allow us to identify which lane + matches the requested byte. Magic constant 0x80200802 used + similarly for NUL termination. */ + mov wtmp2, #0x0401 + movk wtmp2, #0x4010, lsl #16 + dup vrepchr.16b, chrin + bic src, srcin, #31 /* Work with aligned 32-byte hunks. */ + dup vrepmask_c.4s, wtmp2 + mov src_offset, #0 + ands tmp1, srcin, #31 + add vrepmask_0.4s, vrepmask_c.4s, vrepmask_c.4s /* equiv: lsl #1 */ + b.eq L(aligned) + + /* Input string is not 32-byte aligned. Rather than forcing + the padding bytes to a safe value, we calculate the syndrome + for all the bytes, but then mask off those bits of the + syndrome that are related to the padding. */ + ld1 {vdata1.16b, vdata2.16b}, [src], #32 + neg tmp1, tmp1 + cmeq vhas_nul1.16b, vdata1.16b, #0 + cmeq vhas_chr1.16b, vdata1.16b, vrepchr.16b + cmeq vhas_nul2.16b, vdata2.16b, #0 + cmeq vhas_chr2.16b, vdata2.16b, vrepchr.16b + and vhas_nul1.16b, vhas_nul1.16b, vrepmask_0.16b + and vhas_chr1.16b, vhas_chr1.16b, vrepmask_c.16b + and vhas_nul2.16b, vhas_nul2.16b, vrepmask_0.16b + and vhas_chr2.16b, vhas_chr2.16b, vrepmask_c.16b + addp vhas_nul1.16b, vhas_nul1.16b, vhas_nul2.16b // 256->128 + addp vhas_chr1.16b, vhas_chr1.16b, vhas_chr2.16b // 256->128 + addp vhas_nul1.16b, vhas_nul1.16b, vhas_nul1.16b // 128->64 + addp vhas_chr1.16b, vhas_chr1.16b, vhas_chr1.16b // 128->64 + mov nul_match, vhas_nul1.2d[0] + lsl tmp1, tmp1, #1 + mov const_m1, #~0 + mov chr_match, vhas_chr1.2d[0] + lsr tmp3, const_m1, tmp1 + + bic nul_match, nul_match, tmp3 // Mask padding bits. + bic chr_match, chr_match, tmp3 // Mask padding bits. + cbnz nul_match, L(tail) + +L(loop): + cmp chr_match, #0 + csel src_match, src, src_match, ne + csel src_offset, chr_match, src_offset, ne +L(aligned): + ld1 {vdata1.16b, vdata2.16b}, [src], #32 + cmeq vhas_nul1.16b, vdata1.16b, #0 + cmeq vhas_chr1.16b, vdata1.16b, vrepchr.16b + cmeq vhas_nul2.16b, vdata2.16b, #0 + cmeq vhas_chr2.16b, vdata2.16b, vrepchr.16b + addp vend1.16b, vhas_nul1.16b, vhas_nul2.16b // 256->128 + and vhas_chr1.16b, vhas_chr1.16b, vrepmask_c.16b + and vhas_chr2.16b, vhas_chr2.16b, vrepmask_c.16b + addp vhas_chr1.16b, vhas_chr1.16b, vhas_chr2.16b // 256->128 + addp vend1.16b, vend1.16b, vend1.16b // 128->64 + addp vhas_chr1.16b, vhas_chr1.16b, vhas_chr1.16b // 128->64 + mov nul_match, vend1.2d[0] + mov chr_match, vhas_chr1.2d[0] + cbz nul_match, L(loop) + + and vhas_nul1.16b, vhas_nul1.16b, vrepmask_0.16b + and vhas_nul2.16b, vhas_nul2.16b, vrepmask_0.16b + addp vhas_nul1.16b, vhas_nul1.16b, vhas_nul2.16b + addp vhas_nul1.16b, vhas_nul1.16b, vhas_nul1.16b + mov nul_match, vhas_nul1.2d[0] + +L(tail): + /* Work out exactly where the string ends. */ + sub tmp4, nul_match, #1 + eor tmp4, tmp4, nul_match + ands chr_match, chr_match, tmp4 + /* And pick the values corresponding to the last match. */ + csel src_match, src, src_match, ne + csel src_offset, chr_match, src_offset, ne + + /* Count down from the top of the syndrome to find the last match. */ + clz tmp3, src_offset + /* Src_match points beyond the word containing the match, so we can + simply subtract half the bit-offset into the syndrome. Because + we are counting down, we need to go back one more character. */ + add tmp3, tmp3, #2 + sub result, src_match, tmp3, lsr #1 + /* But if the syndrome shows no match was found, then return NULL. */ + cmp src_offset, #0 + csel result, result, xzr, ne + + ret +L(null_search): + b __strchrnul + +END(strrchr) +weak_alias (strrchr, rindex) +libc_hidden_builtin_def (strrchr)