From patchwork Wed Feb 1 17:03:45 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Adhemerval Zanella Netto X-Patchwork-Id: 64099 Return-Path: X-Original-To: patchwork@sourceware.org Delivered-To: patchwork@sourceware.org Received: from server2.sourceware.org (localhost [IPv6:::1]) by sourceware.org (Postfix) with ESMTP id B40143887F69 for ; Wed, 1 Feb 2023 17:06:57 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org B40143887F69 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=sourceware.org; s=default; t=1675271217; bh=J0Npx0KDYzoKUqvn2dnh07FNwFCRlVqx94u6ZtwAyqQ=; h=To:Subject:Date:In-Reply-To:References:List-Id:List-Unsubscribe: List-Archive:List-Post:List-Help:List-Subscribe:From:Reply-To: From; b=qWv9XeFdS4pRgmALCS1xWWtzphW6rRy/hMLEob1Acgo3XS9RugdyQDkj29SZ+JEUl 8YJWn3k8FZxlU/NngSGKfqodH4IufYeXEx67LnnM2QAorrD00CPkDubI/LPBeKLq1p c8DYgOCYsydIw91qzu8erGbDBOfRiJbgxx+mr0Hk= X-Original-To: libc-alpha@sourceware.org Delivered-To: libc-alpha@sourceware.org Received: from mail-oi1-x22b.google.com (mail-oi1-x22b.google.com [IPv6:2607:f8b0:4864:20::22b]) by sourceware.org (Postfix) with ESMTPS id 78A363857BB3 for ; Wed, 1 Feb 2023 17:04:35 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org 78A363857BB3 Received: by mail-oi1-x22b.google.com with SMTP id r205so16256096oib.9 for ; Wed, 01 Feb 2023 09:04:35 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=J0Npx0KDYzoKUqvn2dnh07FNwFCRlVqx94u6ZtwAyqQ=; b=0Qio/aCzTuEnhQVhNTzwBM7vvrTWUmY4dvb6XItuGX+fyByf03445xGVieYM6Q/nJH JACYV+GK+kbq6WzmE54WVnkcp0Xz+7GJqwtC0obMYP2k8AQ1Q5wH3RiTHx8WQc7oEU4P Ap2OSYkdFvCwyxjfBFHtrn7udpDiXSpUI+bNJE/lUx2wy3ecgE8zkDSxREbv5VJuYMLr WsPeAmalrzwCFTSfszK+JDfzbTHnHbbyWJByZtUAfZ5FzExM7V0r/JVk3etgeeC0KqiP C8mJjkiCz0j1TBiPpN3OhQkYjlmIxg6LkcAWFcB2qHu3PVdbqSOmXJNg4ECumKGj1Ljp z3NA== X-Gm-Message-State: AO0yUKVEh0soioLZbBBCuaMNsQ7dXZj/t40sCx2+lDogV/3oLcT5auxP 42yM8vuJFtAm5b9lKB+4Ct4d85oloL+mXsnrXho= X-Google-Smtp-Source: AK7set9dROkDArRkGn8icTQeQBhSuyCRmjbkAH92CCKtu2v+vRWQumMfjqANx0cPdKRsB+7PUlXzRQ== X-Received: by 2002:a05:6808:a09:b0:378:9dbb:d5a8 with SMTP id n9-20020a0568080a0900b003789dbbd5a8mr1401425oij.7.1675271073774; Wed, 01 Feb 2023 09:04:33 -0800 (PST) Received: from mandiga.. ([2804:1b3:a7c2:1887:d2ed:98c2:d2cc:bf06]) by smtp.gmail.com with ESMTPSA id b17-20020a056830311100b006863ccbf067sm8077090ots.74.2023.02.01.09.04.31 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 01 Feb 2023 09:04:33 -0800 (PST) To: libc-alpha@sourceware.org, Richard Henderson , Noah Goldstein , Jeff Law , Xi Ruoyao Subject: [PATCH v11 08/29] string: Improve generic strcmp Date: Wed, 1 Feb 2023 14:03:45 -0300 Message-Id: <20230201170406.303978-9-adhemerval.zanella@linaro.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20230201170406.303978-1-adhemerval.zanella@linaro.org> References: <20230201170406.303978-1-adhemerval.zanella@linaro.org> MIME-Version: 1.0 X-Spam-Status: No, score=-12.7 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, 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 X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-Patchwork-Original-From: Adhemerval Zanella via Libc-alpha From: Adhemerval Zanella Netto Reply-To: Adhemerval Zanella Errors-To: libc-alpha-bounces+patchwork=sourceware.org@sourceware.org Sender: "Libc-alpha" 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 | 118 +++++++++++++++++++++++++++++++++++++++++------- 1 file changed, 102 insertions(+), 16 deletions(-) diff --git a/string/strcmp.c b/string/strcmp.c index 053f5a8d2b..42e24242b6 100644 --- a/string/strcmp.c +++ b/string/strcmp.c @@ -15,33 +15,119 @@ License along with the GNU C Library; if not, see . */ +#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) +{ + /* It can not use index_first_zero_ne because it must not compare past the + final '\0' is present (and final_cmp is called before has_zero check). + */ + for (size_t i = 0; i < sizeof (op_t); i++) + { + unsigned char c1 = extractbyte (w1, i); + unsigned char c2 = extractbyte (w2, i); + if (c1 == '\0' || c1 != c2) + return c1 - c2; + } + return 0; +} + +/* 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