From patchwork Wed Dec 21 23:05:55 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Richard Henderson X-Patchwork-Id: 707993 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Received: from sourceware.org (server1.sourceware.org [209.132.180.131]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ozlabs.org (Postfix) with ESMTPS id 3tkVg42g7wz9snm for ; Thu, 22 Dec 2016 10:07:44 +1100 (AEDT) Authentication-Results: ozlabs.org; dkim=pass (1024-bit key; secure) header.d=sourceware.org header.i=@sourceware.org header.b="fb7Wvu10"; dkim-atps=neutral DomainKey-Signature: a=rsa-sha1; c=nofws; d=sourceware.org; h=list-id :list-unsubscribe:list-subscribe:list-archive:list-post :list-help:sender:from:to:subject:date:message-id:in-reply-to :references; q=dns; s=default; b=EapVuST074xd60lg4XPS/xmigz+p2TW NQgjRyZEmzprvOK9LiAe/eRx1Oz6wfDtdTzuABuS5UGbC0mrDoHCGnMHIT5n5L40 P8HiYPbebNXfz+qg7Ad0Bp82YSfGgCahIVFI6f7p5V83WCMovABRnzImSrWQXRB9 Zt76qLQn68Ns= DKIM-Signature: v=1; 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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=PZ5KX+bz0P4TZqRgjzJ3nQP6ZWu1zFec7LwbxTXN7HU=; b=FJxn8pN8sVGf1VpvfPJQjo6oD/lZmLvCSeqrBplFib8fEE7Mj4uR5K+FzEHOxBn0ET 85HxwN1/nj7euY1MVfraWjq4gw9KbRca+XhJi3nhUi3ya5Xj943Fd1R7Y6HHx8wLhmGw jiq10MMSqZ3jtXRt2XyTGoCYidoGfmOvtSITlAWi3XL4QDWYC7W3tfGv7lSQHc6VPl2M Bjm5fRZgOSOgZOvwGtFV1eCTf6GEyGGXr849tnmbfzIGdtMV40Gn+0qtA1a7nVht7P5f aqemg79sh92DPQv07HiprNKAlWHvv1AsIYBwsqWBSA4Mp3Qs6DJklClM+xg9WHjixzpS +kWg== X-Gm-Message-State: AIkVDXIG7tHtdyn0suX37jSXusBrmEp7NBpyDPxPRvnvKfY6+cPp210B6emtZtwnNeZsVQ== X-Received: by 10.84.210.76 with SMTP id z70mr13160645plh.111.1482361572456; Wed, 21 Dec 2016 15:06:12 -0800 (PST) From: Richard Henderson To: libc-alpha@sourceware.org Subject: [PATCH v2 06/16] Improve generic strchrnul Date: Wed, 21 Dec 2016 15:05:55 -0800 Message-Id: <20161221230605.28638-7-rth@twiddle.net> In-Reply-To: <20161221230605.28638-1-rth@twiddle.net> References: <20161221230605.28638-1-rth@twiddle.net> [BZ #5806] * string/strchrnul.c: Use string-fzb.h, string-fzi.h. --- string/strchrnul.c | 142 +++++++++-------------------------------------------- 1 file changed, 24 insertions(+), 118 deletions(-) diff --git a/string/strchrnul.c b/string/strchrnul.c index 629db46..7090c05 100644 --- a/string/strchrnul.c +++ b/string/strchrnul.c @@ -21,146 +21,52 @@ . */ #include -#include #include +#include +#include +#include #undef __strchrnul #undef strchrnul -#ifndef STRCHRNUL -# define STRCHRNUL __strchrnul +#ifdef STRCHRNUL +# define __strchrnul STRCHRNUL #endif /* Find the first occurrence of C in S or the final NUL byte. */ char * -STRCHRNUL (const char *s, int c_in) +__strchrnul (const char *s, int c_in) { const unsigned char *char_ptr; - const unsigned long int *longword_ptr; - unsigned long int longword, magic_bits, charmask; + const op_t *word_ptr; + op_t word, repeated_c; + uintptr_t i, align, found; unsigned char c; c = (unsigned char) c_in; + char_ptr = (const unsigned char *) s; /* 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) + Do this until CHAR_PTR is aligned on a word boundary. */ + align = -(uintptr_t)char_ptr % sizeof(word); + for (i = 0; i < align; ++i, ++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 + return (char *) char_ptr; - 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 word, each of whose bytes is C. */ + repeated_c = ((op_t)-1 / 0xff) * c; - /* 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 (;;) + word_ptr = (op_t *) char_ptr; + do { - /* 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; - } - } + word = *word_ptr++; } + while (!has_zero_eq (word, repeated_c)); - /* This should never happen. */ - return NULL; + found = index_first_zero_eq (word, repeated_c); + return (char *) (word_ptr - 1) + found; } +#ifndef STRCHRNUL weak_alias (__strchrnul, strchrnul) +#endif