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([2804:1b3:a7c0:a93a:e8a0:dd55:3328:997]) by smtp.gmail.com with ESMTPSA id r5-20020a4a83c5000000b0049ee88e86f9sm6202193oog.10.2023.01.10.13.01.28 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 10 Jan 2023 13:01:29 -0800 (PST) To: libc-alpha@sourceware.org, Noah Goldstein , Richard Henderson Cc: Adhemerval Zanella Netto Subject: [PATCH v6 07/17] string: Improve generic strchr Date: Tue, 10 Jan 2023 18:00:56 -0300 Message-Id: <20230110210106.1457686-8-adhemerval.zanella@linaro.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20230110210106.1457686-1-adhemerval.zanella@linaro.org> References: <20230110210106.1457686-1-adhemerval.zanella@linaro.org> MIME-Version: 1.0 X-Spam-Status: No, score=-12.6 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+patch=linaro.org@sourceware.org Sender: "Libc-alpha" From: Adhemerval Zanella Netto New algorithm now calls strchrnul. Checked on x86_64-linux-gnu, i686-linux-gnu, powerpc-linux-gnu, and powerpc64-linux-gnu by removing the arch-specific assembly implementation and disabling multi-arch (it covers both LE and BE for 64 and 32 bits). --- string/strchr.c | 159 ++-------------------------------------- sysdeps/s390/strchr-c.c | 11 +-- 2 files changed, 14 insertions(+), 156 deletions(-) diff --git a/string/strchr.c b/string/strchr.c index 1572b8b42e..30c3eb10f2 100644 --- a/string/strchr.c +++ b/string/strchr.c @@ -21,165 +21,22 @@ . */ #include -#include #undef strchr +#undef index -#ifndef STRCHR -# define STRCHR strchr +#ifdef STRCHR +# define strchr STRCHR #endif /* Find the first occurrence of C in S. */ char * -STRCHR (const char *s, int c_in) +strchr (const char *s, int c_in) { - const unsigned char *char_ptr; - const unsigned long int *longword_ptr; - unsigned long int longword, magic_bits, charmask; - unsigned char c; - - c = (unsigned char) c_in; - - /* Handle the first few characters by reading one character at a time. - Do this until CHAR_PTR is aligned on a longword boundary. */ - for (char_ptr = (const unsigned char *) s; - ((unsigned long int) char_ptr & (sizeof (longword) - 1)) != 0; - ++char_ptr) - if (*char_ptr == c) - return (void *) char_ptr; - else if (*char_ptr == '\0') - return NULL; - - /* All these elucidatory comments refer to 4-byte longwords, - but the theory applies equally well to 8-byte longwords. */ - - longword_ptr = (unsigned long int *) char_ptr; - - /* Bits 31, 24, 16, and 8 of this number are zero. Call these bits - the "holes." Note that there is a hole just to the left of - each byte, with an extra at the end: - - bits: 01111110 11111110 11111110 11111111 - bytes: AAAAAAAA BBBBBBBB CCCCCCCC DDDDDDDD - - The 1-bits make sure that carries propagate to the next 0-bit. - The 0-bits provide holes for carries to fall into. */ - magic_bits = -1; - magic_bits = magic_bits / 0xff * 0xfe << 1 >> 1 | 1; - - /* Set up a longword, each of whose bytes is C. */ - charmask = c | (c << 8); - charmask |= charmask << 16; - if (sizeof (longword) > 4) - /* Do the shift in two steps to avoid a warning if long has 32 bits. */ - charmask |= (charmask << 16) << 16; - if (sizeof (longword) > 8) - abort (); - - /* Instead of the traditional loop which tests each character, - we will test a longword at a time. The tricky part is testing - if *any of the four* bytes in the longword in question are zero. */ - for (;;) - { - /* We tentatively exit the loop if adding MAGIC_BITS to - LONGWORD fails to change any of the hole bits of LONGWORD. - - 1) Is this safe? Will it catch all the zero bytes? - Suppose there is a byte with all zeros. Any carry bits - propagating from its left will fall into the hole at its - least significant bit and stop. Since there will be no - carry from its most significant bit, the LSB of the - byte to the left will be unchanged, and the zero will be - detected. - - 2) Is this worthwhile? Will it ignore everything except - zero bytes? Suppose every byte of LONGWORD has a bit set - somewhere. There will be a carry into bit 8. If bit 8 - is set, this will carry into bit 16. If bit 8 is clear, - one of bits 9-15 must be set, so there will be a carry - into bit 16. Similarly, there will be a carry into bit - 24. If one of bits 24-30 is set, there will be a carry - into bit 31, so all of the hole bits will be changed. - - The one misfire occurs when bits 24-30 are clear and bit - 31 is set; in this case, the hole at bit 31 is not - changed. If we had access to the processor carry flag, - we could close this loophole by putting the fourth hole - at bit 32! - - So it ignores everything except 128's, when they're aligned - properly. - - 3) But wait! Aren't we looking for C as well as zero? - Good point. So what we do is XOR LONGWORD with a longword, - each of whose bytes is C. This turns each byte that is C - into a zero. */ - - longword = *longword_ptr++; - - /* Add MAGIC_BITS to LONGWORD. */ - if ((((longword + magic_bits) - - /* Set those bits that were unchanged by the addition. */ - ^ ~longword) - - /* Look at only the hole bits. If any of the hole bits - are unchanged, most likely one of the bytes was a - zero. */ - & ~magic_bits) != 0 - - /* That caught zeroes. Now test for C. */ - || ((((longword ^ charmask) + magic_bits) ^ ~(longword ^ charmask)) - & ~magic_bits) != 0) - { - /* Which of the bytes was C or zero? - If none of them were, it was a misfire; continue the search. */ - - const unsigned char *cp = (const unsigned char *) (longword_ptr - 1); - - if (*cp == c) - return (char *) cp; - else if (*cp == '\0') - return NULL; - if (*++cp == c) - return (char *) cp; - else if (*cp == '\0') - return NULL; - if (*++cp == c) - return (char *) cp; - else if (*cp == '\0') - return NULL; - if (*++cp == c) - return (char *) cp; - else if (*cp == '\0') - return NULL; - if (sizeof (longword) > 4) - { - if (*++cp == c) - return (char *) cp; - else if (*cp == '\0') - return NULL; - if (*++cp == c) - return (char *) cp; - else if (*cp == '\0') - return NULL; - if (*++cp == c) - return (char *) cp; - else if (*cp == '\0') - return NULL; - if (*++cp == c) - return (char *) cp; - else if (*cp == '\0') - return NULL; - } - } - } - - return NULL; + char *r = __strchrnul (s, c_in); + return (*(unsigned char *)r == (unsigned char)c_in) ? r : NULL; } - -#ifdef weak_alias -# undef index +#ifndef STRCHR weak_alias (strchr, index) -#endif libc_hidden_builtin_def (strchr) +#endif diff --git a/sysdeps/s390/strchr-c.c b/sysdeps/s390/strchr-c.c index c00f2cceea..90822ae0f4 100644 --- a/sysdeps/s390/strchr-c.c +++ b/sysdeps/s390/strchr-c.c @@ -21,13 +21,14 @@ #if HAVE_STRCHR_C # if HAVE_STRCHR_IFUNC # define STRCHR STRCHR_C -# undef weak_alias +# endif + +# include + +# if HAVE_STRCHR_IFUNC # if defined SHARED && IS_IN (libc) -# undef libc_hidden_builtin_def -# define libc_hidden_builtin_def(name) \ - __hidden_ver1 (__strchr_c, __GI_strchr, __strchr_c); +__hidden_ver1 (__strchr_c, __GI_strchr, __strchr_c); # endif # endif -# include #endif