From patchwork Wed May 27 09:11:48 2015 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Ondrej Bilka X-Patchwork-Id: 6936 Received: (qmail 101334 invoked by alias); 27 May 2015 09:12:14 -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 101325 invoked by uid 89); 27 May 2015 09:12:14 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=0.7 required=5.0 tests=AWL, BAYES_50, FREEMAIL_FROM, SPF_NEUTRAL autolearn=no version=3.3.2 X-HELO: popelka.ms.mff.cuni.cz Date: Wed, 27 May 2015 11:11:48 +0200 From: =?utf-8?B?T25kxZllaiBCw61sa2E=?= To: libc-alpha@sourceware.org Subject: [PATCH 2/* v2] Optimize generic strchrnul and strchr Message-ID: <20150527091148.GB27814@domone> References: <20150527060121.GA19105@domone> <20150527063544.GA3360@domone> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20150527063544.GA3360@domone> User-Agent: Mutt/1.5.20 (2009-06-14) On Wed, May 27, 2015 at 08:35:44AM +0200, Ondřej Bílka wrote: > This is my generic strchr algorithm resubmitted to use skeleton. > > Idea to split into cases c<128 and c>128 didn't change. > > So comments? How this perform on different architectures? > This also needed to change as I used older strchr wrapper. Here is correct one. * string/strchr.c: Use skeleton. * string/strchrnul.c: Likewise. diff --git a/string/strchr.c b/string/strchr.c index 5f90075..e7c2e4c 100644 --- a/string/strchr.c +++ b/string/strchr.c @@ -1,10 +1,5 @@ /* Copyright (C) 1991-2015 Free Software Foundation, Inc. This file is part of the GNU C Library. - Based on strlen implementation by Torbjorn Granlund (tege@sics.se), - with help from Dan Sahlin (dan@sics.se) and - bug fix and commentary by Jim Blandy (jimb@ai.mit.edu); - adaptation to strchr suggested by Dick Karpinski (dick@cca.ucsf.edu), - and implemented by Roland McGrath (roland@ai.mit.edu). The GNU C Library is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public @@ -21,166 +16,21 @@ . */ #include -#include - #undef strchr +#undef index + +#define AS_STRCHR +#define STRCHRNUL strchrnul_static +#include "string/strchrnul.c" + -/* Find the first occurrence of C in S. */ char * 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. */ - switch (sizeof (longword)) - { - case 4: magic_bits = 0x7efefeffL; break; - case 8: magic_bits = ((0x7efefefeL << 16) << 16) | 0xfefefeffL; break; - default: - abort (); - } - - /* 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; + unsigned char c = (unsigned char) c_in; + unsigned char *r = (unsigned char *) STRCHRNUL (s, c); + return (*r == c) ? (char *) r : NULL; } -#ifdef weak_alias -#undef index weak_alias (strchr, index) -#endif libc_hidden_builtin_def (strchr) diff --git a/string/strchrnul.c b/string/strchrnul.c index 2678f1d..95fa11d 100644 --- a/string/strchrnul.c +++ b/string/strchrnul.c @@ -1,10 +1,5 @@ /* Copyright (C) 1991-2015 Free Software Foundation, Inc. This file is part of the GNU C Library. - Based on strlen implementation by Torbjorn Granlund (tege@sics.se), - with help from Dan Sahlin (dan@sics.se) and - bug fix and commentary by Jim Blandy (jimb@ai.mit.edu); - adaptation to strchr suggested by Dick Karpinski (dick@cca.ucsf.edu), - and implemented by Roland McGrath (roland@ai.mit.edu). The GNU C Library is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public @@ -21,153 +16,63 @@ . */ #include -#include #include -#undef __strchrnul #undef strchrnul +#undef __strchrnul + +/* Return the length of the null-terminated string STR. Scan for + the null terminator quickly by testing four bytes at a time. */ + +/* Here idea is still use the result of expression + contains_zero (*p) | contains_zero (*p ^ cmask) + but we can optimize it by using commutativity of operations. */ + +#include "string/common.h" +/* #define EXPRESSION(s, cmask) (((((s & add) + add) & (((s & add) ^ cmask) + add)) | s) ^ high_bits) & high_bits */ + +#define EXPRESSION(s, cmask) (contains_zero(s) | contains_zero (s ^ cmask)) +#include "string/skeleton.h" #ifndef STRCHRNUL # define STRCHRNUL __strchrnul #endif -/* Find the first occurrence of C in S or the final NUL byte. */ +#ifdef AS_STRCHR +static __always_inline +#endif char * -STRCHRNUL (s, c_in) - const char *s; - int c_in; +STRCHRNUL (const char *s_in, 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 || *char_ptr == '\0') - return (void *) char_ptr; - - /* 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. */ - switch (sizeof (longword)) - { - case 4: magic_bits = 0x7efefeffL; break; - case 8: magic_bits = ((0x7efefefeL << 16) << 16) | 0xfefefeffL; break; - default: - abort (); - } - - /* 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 (;;) + char *s_aligned; + unsigned long int mask; + const unsigned long int *lptr; + char *s = (char *) s_in; + unsigned char c = (unsigned char) c_in; + unsigned long int cmask = c * ones; + if (__glibc_unlikely (c > 127)) { - /* 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 || *cp == '\0') - return (char *) cp; - if (*++cp == c || *cp == '\0') - return (char *) cp; - if (*++cp == c || *cp == '\0') - return (char *) cp; - if (*++cp == c || *cp == '\0') - return (char *) cp; - if (sizeof (longword) > 4) - { - if (*++cp == c || *cp == '\0') - return (char *) cp; - if (*++cp == c || *cp == '\0') - return (char *) cp; - if (*++cp == c || *cp == '\0') - return (char *) cp; - if (*++cp == c || *cp == '\0') - return (char *) cp; - } - } + s_aligned = PTR_ALIGN_DOWN (s, LSIZE); + lptr = (const unsigned long int *) s_aligned; + mask = (contains_zero(*lptr) | contains_zero (*lptr ^ cmask)) + >> (8 * (s - s_aligned)); + + if (mask) + return s + first_nonzero_byte (mask); + + while (1) + { + s_aligned += LSIZE; + lptr = (const unsigned long int *) s_aligned; + mask = contains_zero(*lptr) | contains_zero (*lptr ^ cmask); + if (mask) + return s_aligned + first_nonzero_byte (mask); + } } - - /* This should never happen. */ - return NULL; + else + return string_skeleton (s, c, 0); } +#ifndef AS_STRCHR weak_alias (__strchrnul, strchrnul) +#endif