From patchwork Wed Dec 21 23:05:57 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Richard Henderson X-Patchwork-Id: 18625 Received: (qmail 51720 invoked by alias); 21 Dec 2016 23:06:23 -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 51244 invoked by uid 89); 21 Dec 2016 23:06:20 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-1.1 required=5.0 tests=BAYES_00, FREEMAIL_ENVFROM_END_DIGIT, FREEMAIL_FROM, RCVD_IN_DNSWL_NONE, RCVD_IN_SORBS_SPAM, SPF_PASS autolearn=no version=3.3.2 spammy=Hx-spam-relays-external:74.125.83.68, H*RU:74.125.83.68 X-HELO: mail-pg0-f68.google.com X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:from:to:subject:date:message-id :in-reply-to:references; bh=eToIF0kxglPPrmNJY8eZ6bwH6koCS/F+sxsshrKs+u8=; b=LicfsSSZkz/kSgtigaAo5voWMnNPQ4+sqwzchdWSgxW2TaN3DyPDN3amaIywenXvVQ HGI/PrrNRmws7Uj+8elW/5FXk226p1kInAUpaO6KoSeTTJuejvKGsgpwDFXl5UZUbGrw 8tWcTlN+984Iktt/bUYBv0+XIoSzbVmrYZXV84hzUH29L4VGB5tDUZJd2NjrGfc17wH6 agZe1MYgnC98kAhbsSWFHaoixv89EkjhU+jjhmFUQQGu6ooNf91HhJcxtwwIaPbRE6tC 3lTmvTGS2YQEqK1cfTlaHj+E5oraCUpb/tEmCTXfOdTRiwxTTA3451HI4+YDgEnPWL2W cdsQ== X-Gm-Message-State: AIkVDXKC1E3ZUFzCeBmjfW2kOtaSkgIahMqTliku6zwKjB5D/pAhFGuo2TMWsVP+qLKYlg== X-Received: by 10.99.238.17 with SMTP id e17mr11836118pgi.58.1482361574312; Wed, 21 Dec 2016 15:06:14 -0800 (PST) From: Richard Henderson To: libc-alpha@sourceware.org Subject: [PATCH v2 08/16] Improve generic memrchr Date: Wed, 21 Dec 2016 15:05:57 -0800 Message-Id: <20161221230605.28638-9-rth@twiddle.net> In-Reply-To: <20161221230605.28638-1-rth@twiddle.net> References: <20161221230605.28638-1-rth@twiddle.net> [BZ #5806] * string/memrchr.c: Use string-fzb.h, string-fzi.h. --- string/memrchr.c | 205 +++++++++++++++---------------------------------------- 1 file changed, 55 insertions(+), 150 deletions(-) diff --git a/string/memrchr.c b/string/memrchr.c index b9b0c9e..ed9ceaf 100644 --- a/string/memrchr.c +++ b/string/memrchr.c @@ -21,180 +21,85 @@ License along with the GNU C Library; if not, see . */ -#include - -#ifdef HAVE_CONFIG_H -# include -#endif - -#undef __ptr_t -#define __ptr_t void * - -#if defined _LIBC -# include -# include -#endif - -#if defined HAVE_LIMITS_H || defined _LIBC -# include -#endif - -#define LONG_MAX_32_BITS 2147483647 - -#ifndef LONG_MAX -# define LONG_MAX LONG_MAX_32_BITS -#endif - -#include +#include +#include +#include +#include +#include +#include #undef __memrchr #undef memrchr -#ifndef weak_alias -# define __memrchr memrchr -#endif - /* Search no more than N bytes of S for C. */ -__ptr_t -#ifndef MEMRCHR -__memrchr -#else -MEMRCHR + +#ifdef MEMRCHR +# define __memrchr MEMRCHR #endif - (const __ptr_t s, int c_in, size_t n) + +void * +__memrchr (const void *s, int c_in, size_t n) { - const unsigned char *char_ptr; - const unsigned long int *longword_ptr; - unsigned long int longword, magic_bits, charmask; + const unsigned char *char_ptr = (const unsigned char *) s + n; + const op_t *word_ptr; + op_t word, repeated_c; + uintptr_t i, align; unsigned char c; c = (unsigned char) c_in; /* Handle the last 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 + n; - n > 0 && ((unsigned long int) char_ptr - & (sizeof (longword) - 1)) != 0; - --n) + Do this until CHAR_PTR is aligned on a word boundary, or + the entirety of small inputs. */ + align = (uintptr_t)char_ptr % sizeof (word); + if (n < OP_T_THRES || align > n) + align = n; + for (i = 0; i < align; ++i) if (*--char_ptr == c) - return (__ptr_t) char_ptr; - - /* All these elucidatory comments refer to 4-byte longwords, - but the theory applies equally well to 8-byte longwords. */ - - longword_ptr = (const 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: + return (void *) char_ptr; - bits: 01111110 11111110 11111110 11111111 - bytes: AAAAAAAA BBBBBBBB CCCCCCCC DDDDDDDD + /* Set up a word, each of whose bytes is C. */ + repeated_c = ((op_t)-1 / 0xff) * c; - 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; + word_ptr = (const op_t *) char_ptr; + n -= align; + if (__glibc_unlikely (n == 0)) + return NULL; - /* Set up a longword, each of whose bytes is C. */ - charmask = c | (c << 8); - charmask |= charmask << 16; -#if LONG_MAX > LONG_MAX_32_BITS - charmask |= charmask << 32; -#endif - - /* 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. */ - while (n >= sizeof (longword)) + /* Loop while we have at least one word remaining. */ + while (n >= sizeof (word)) { - /* 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, not 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 ^ charmask; - - /* 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) + word = *--word_ptr; + if (has_eq (word, repeated_c)) { - /* Which of the bytes was C? If none of them were, it was - a misfire; continue the search. */ - - const unsigned char *cp = (const unsigned char *) longword_ptr; - -#if LONG_MAX > 2147483647 - if (cp[7] == c) - return (__ptr_t) &cp[7]; - if (cp[6] == c) - return (__ptr_t) &cp[6]; - if (cp[5] == c) - return (__ptr_t) &cp[5]; - if (cp[4] == c) - return (__ptr_t) &cp[4]; -#endif - if (cp[3] == c) - return (__ptr_t) &cp[3]; - if (cp[2] == c) - return (__ptr_t) &cp[2]; - if (cp[1] == c) - return (__ptr_t) &cp[1]; - if (cp[0] == c) - return (__ptr_t) cp; + word ^= repeated_c; + goto found; } - - n -= sizeof (longword); + n -= sizeof (word); } - char_ptr = (const unsigned char *) longword_ptr; - - while (n-- > 0) + /* Handle any remaining portion of a word. */ + if (n > 0) { - if (*--char_ptr == c) - return (__ptr_t) char_ptr; - } + word = *--word_ptr ^ repeated_c; - return 0; + /* Mask out the garbage bytes at the front of WORD. */ + op_t m = -1; + if (__BYTE_ORDER == __LITTLE_ENDIAN) + m >>= n * CHAR_BIT; + else + m <<= n * CHAR_BIT; + word |= m; + + if (has_zero (word)) + { + found: + return (char *) word_ptr + index_last_zero (word); + } + } + return NULL; } + #ifndef MEMRCHR -# ifdef weak_alias weak_alias (__memrchr, memrchr) -# endif #endif