From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ej1-x62b.google.com (mail-ej1-x62b.google.com [IPv6:2a00:1450:4864:20::62b]) by sourceware.org (Postfix) with ESMTPS id B138F38493E5 for ; Fri, 3 Feb 2023 23:25:16 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org B138F38493E5 Authentication-Results: sourceware.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=gmail.com Received: by mail-ej1-x62b.google.com with SMTP id mc11so19486629ejb.10 for ; Fri, 03 Feb 2023 15:25:16 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:from:to:cc:subject:date:message-id:reply-to; bh=Ui0J94tpoM3eoGYoshPYxQ9At2q8SUAU3rNboBRCHEM=; b=pQSedihyoqg+YehHijuxVuC2SAPRRdam/yMgRRagj8MjJviw+mNbIZZQbZkcXRvLAk D0ImHVzGurQDRNBM04cLvt2X8e0bI9k+1G6nkdIeprEb596//olUi2IxlWOIuvyuj8du 7Jt6SJyXxaTdbAck66JH9ciSnXX6lyAj0s6Jaqwojy/5PZS9GBGVJ1hIwPIy6ZS7I1Gc brGcU20tUHej+vLZjlWJzXTOQpNvKxnuwfKLa5Ayg4zccX+hNoMgFjp0VZpG2N98iLGU ZP6mfZy3/wp+0ZPLD8SdvB59S+YjVDDYjyzsfVzXPHJ7rHFPBOpHCH7wJBXaivCgFOhI zPBA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=Ui0J94tpoM3eoGYoshPYxQ9At2q8SUAU3rNboBRCHEM=; b=phoDyMuM+oLzJji3bWePq3KcoRHaK89zVDfRwtn8m0Dag1iGQ7+YqqOWjL1PSzER0w pz0hfwbIyRLnRVDVZhf6ZliJ+dhGgrRmnjO0RcuHNXwlrtHY/JzkYHe+55ZDJulKnOhV gcLx1dnDLDMPatpeNAQCWR9pY92bES+0VluWHwuu2P8PxuOIp0H778UsY4gbS39FWhZn CWWR4BdPxC1SOBQLAFKvKa7olAq16FiQTBTvRbniVM4BkgLqg7CF5Z/JaGcGynZYKNpe NG24u9Jg8k7IwVQ+Tdb32sTV0sotkDuxTNJGj6leHmumeKPMvtXRKkFyjZ+2hH0XYEsA wkCA== X-Gm-Message-State: AO0yUKUmgDas8F39xLXa+XtOlETPQ31xAa8UtqR9SX9x4/kZrQTdHc90 KKhtnuiWx1AIn7JWzgPyO7kn/1vLw0cCw43aFG8= X-Google-Smtp-Source: AK7set+cT8+zEU+6eXQCWy7yXER6l+Ni6EGVvIFbkjm4Rf45cWvMx6O6MtfNbtQ8Sqe8Sf7gpki0BRUzsh5oEJNV3Eg= X-Received: by 2002:a17:907:7670:b0:87b:db55:f3e5 with SMTP id kk16-20020a170907767000b0087bdb55f3e5mr3500556ejc.289.1675466715373; Fri, 03 Feb 2023 15:25:15 -0800 (PST) MIME-Version: 1.0 References: <20230202181149.2181553-1-adhemerval.zanella@linaro.org> <20230202181149.2181553-8-adhemerval.zanella@linaro.org> In-Reply-To: <20230202181149.2181553-8-adhemerval.zanella@linaro.org> From: Noah Goldstein Date: Fri, 3 Feb 2023 17:25:04 -0600 Message-ID: Subject: Re: [PATCH v12 07/31] string: Improve generic strcmp To: Adhemerval Zanella Cc: libc-alpha@sourceware.org, Richard Henderson , Jeff Law , Xi Ruoyao Content-Type: text/plain; charset="UTF-8" X-Spam-Status: No, score=-9.7 required=5.0 tests=BAYES_00,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,FREEMAIL_FROM,GIT_PATCH_0,KAM_SHORT,RCVD_IN_DNSWL_NONE,SPF_HELO_NONE,SPF_PASS,TXREP autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: On Thu, Feb 2, 2023 at 12:12 PM Adhemerval Zanella wrote: > > It follows the strategy: > > - Align the first input to word boundary using byte operations. > > - If second input is also word aligned, read a word per time, check for > null (using has_zero), and check final words using byte operation. > > - If second input is not word aligned, loop by aligning the source, and > merging the result of two reads. Similar to aligned case, check for > null with has_zero, and check final words using byte operation. > > Checked on x86_64-linux-gnu, i686-linux-gnu, powerpc64-linux-gnu, > and powerpc-linux-gnu by removing the arch-specific assembly > implementation and disabling multi-arch (it covers both LE and BE > for 64 and 32 bits). > > Co-authored-by: Richard Henderson > --- > string/strcmp.c | 110 +++++++++++++++++++++++++++++++++++++++++------- > 1 file changed, 94 insertions(+), 16 deletions(-) > > diff --git a/string/strcmp.c b/string/strcmp.c > index 053f5a8d2b..11ec8bac81 100644 > --- a/string/strcmp.c > +++ b/string/strcmp.c > @@ -15,33 +15,111 @@ > License along with the GNU C Library; if not, see > . */ > > +#include > +#include > +#include > +#include > #include > +#include > > -#undef strcmp > - > -#ifndef STRCMP > -# define STRCMP strcmp > +#ifdef STRCMP > +# define strcmp STRCMP > #endif > > +static inline int > +final_cmp (const op_t w1, const op_t w2) > +{ > + unsigned int idx = index_first_zero_ne (w1, w2); > + return extractbyte (w1, idx) - extractbyte (w2, idx); > +} > + > +/* Aligned loop: if a difference is found, exit to compare the bytes. Else > + if a zero is found we have equal strings. */ > +static inline int > +strcmp_aligned_loop (const op_t *x1, const op_t *x2, op_t w1) > +{ > + op_t w2 = *x2++; > + > + while (w1 == w2) > + { > + if (has_zero (w1)) > + return 0; > + w1 = *x1++; > + w2 = *x2++; > + } > + > + return final_cmp (w1, w2); > +} > + > +/* Unaligned loop: align the first partial of P2, with 0xff for the rest of > + the bytes so that we can also apply the has_zero test to see if we have > + already reached EOS. If we have, then we can simply fall through to the > + final comparison. */ > +static inline int > +strcmp_unaligned_loop (const op_t *x1, const op_t *x2, op_t w1, uintptr_t ofs) > +{ > + op_t w2a = *x2++; > + uintptr_t sh_1 = ofs * CHAR_BIT; > + uintptr_t sh_2 = sizeof(op_t) * CHAR_BIT - sh_1; > + > + op_t w2 = MERGE (w2a, sh_1, (op_t)-1, sh_2); > + if (!has_zero (w2)) > + { > + op_t w2b; > + > + /* Unaligned loop. The invariant is that W2B, which is "ahead" of W1, > + does not contain end-of-string. Therefore it is safe (and necessary) > + to read another word from each while we do not have a difference. */ > + while (1) > + { > + w2b = *x2++; > + w2 = MERGE (w2a, sh_1, w2b, sh_2); > + if (w1 != w2) > + return final_cmp (w1, w2); > + if (has_zero (w2b)) > + break; > + w1 = *x1++; > + w2a = w2b; > + } > + > + /* Zero found in the second partial of P2. If we had EOS in the aligned > + word, we have equality. */ > + if (has_zero (w1)) > + return 0; > + > + /* Load the final word of P1 and align the final partial of P2. */ > + w1 = *x1++; > + w2 = MERGE (w2b, sh_1, 0, sh_2); > + } > + > + return final_cmp (w1, w2); > +} > + > /* Compare S1 and S2, returning less than, equal to or > greater than zero if S1 is lexicographically less than, > equal to or greater than S2. */ > int > -STRCMP (const char *p1, const char *p2) > +strcmp (const char *p1, const char *p2) > { > - const unsigned char *s1 = (const unsigned char *) p1; > - const unsigned char *s2 = (const unsigned char *) p2; > - unsigned char c1, c2; > - > - do > + /* Handle the unaligned bytes of p1 first. */ > + uintptr_t n = -(uintptr_t)p1 % sizeof(op_t); > + for (int i = 0; i < n; ++i) > { > - c1 = (unsigned char) *s1++; > - c2 = (unsigned char) *s2++; > - if (c1 == '\0') > - return c1 - c2; > + unsigned char c1 = *p1++; > + unsigned char c2 = *p2++; > + int diff = c1 - c2; > + if (c1 == '\0' || diff != 0) > + return diff; > } > - while (c1 == c2); > > - return c1 - c2; > + /* P1 is now aligned to op_t. P2 may or may not be. */ > + const op_t *x1 = (const op_t *) p1; > + op_t w1 = *x1++; > + uintptr_t ofs = (uintptr_t) p2 % sizeof(op_t); > + return ofs == 0 > + ? strcmp_aligned_loop (x1, (const op_t *)p2, w1) > + : strcmp_unaligned_loop (x1, (const op_t *)(p2 - ofs), w1, ofs); > } > +#ifndef STRCMP > libc_hidden_builtin_def (strcmp) > +#endif > -- > 2.34.1 > LGTM. Reviewed-by: Noah Goldstein