From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2A271C35278 for ; Mon, 7 Feb 2022 16:33:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1389818AbiBGQaq (ORCPT ); Mon, 7 Feb 2022 11:30:46 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:32866 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1380060AbiBGQ03 (ORCPT ); Mon, 7 Feb 2022 11:26:29 -0500 Received: from 1wt.eu (wtarreau.pck.nerim.net [62.212.114.60]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 12693C0401CF for ; Mon, 7 Feb 2022 08:26:27 -0800 (PST) Received: (from willy@localhost) by pcw.home.local (8.15.2/8.15.2/Submit) id 217GOcV3014398; Mon, 7 Feb 2022 17:24:38 +0100 From: Willy Tarreau To: "Paul E . McKenney" Cc: Mark Brown , linux-kernel@vger.kernel.org, Willy Tarreau Subject: [PATCH 15/42] tools/nolibc/stdlib: replace the ltoa() function with more efficient ones Date: Mon, 7 Feb 2022 17:23:27 +0100 Message-Id: <20220207162354.14293-16-w@1wt.eu> X-Mailer: git-send-email 2.17.5 In-Reply-To: <20220207162354.14293-1-w@1wt.eu> References: <20220207162354.14293-1-w@1wt.eu> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The original ltoa() function and the reentrant one ltoa_r() present a number of drawbacks. The divide by 10 generates calls to external code from libgcc_s, and the number does not necessarily start at the beginning of the buffer. Let's rewrite these functions so that they do not involve a divide and only use loops on powers of 10, and implement both signed and unsigned variants, always starting from the buffer's first character. Instead of using a static buffer for each function, we're now using a common one. In order to avoid confusion with the ltoa() name, the new functions are called itoa_r() and utoa_r() to distinguish the signed and unsigned versions, and for convenience for their callers, these functions now reutrn the number of characters emitted. The ltoa_r() function is just an inline mapping to the signed one and which returns the buffer. The functions are quite small (86 bytes on x86_64, 68 on armv7) and do not depend anymore on external code. Signed-off-by: Willy Tarreau --- tools/include/nolibc/stdlib.h | 107 +++++++++++++++++++++++++++------- 1 file changed, 87 insertions(+), 20 deletions(-) diff --git a/tools/include/nolibc/stdlib.h b/tools/include/nolibc/stdlib.h index 84fc4353fb01..dbb45631c7ca 100644 --- a/tools/include/nolibc/stdlib.h +++ b/tools/include/nolibc/stdlib.h @@ -12,6 +12,13 @@ #include "types.h" #include "sys.h" + +/* Buffer used to store int-to-ASCII conversions. Will only be implemented if + * any of the related functions is implemented. The area is large enough to + * store "18446744073709551615" or "-9223372036854775808" and the final zero. + */ +static __attribute__((unused)) char itoa_buffer[21]; + /* * As much as possible, please keep functions alphabetically sorted. */ @@ -45,36 +52,96 @@ int atoi(const char *s) return atol(s); } -/* performs the opposite of atol() using a user-fed buffer. The buffer must be - * at least 21 bytes long (large enough for "-9223372036854775808"). +/* Converts the unsigned long integer to its string representation into + * buffer , which must be long enough to store the number and the + * trailing zero (21 bytes for 18446744073709551615 in 64-bit, 11 for + * 4294967295 in 32-bit). The buffer is filled from the first byte, and the + * number of characters emitted (not counting the trailing zero) is returned. + * The function is constructed in a way to optimize the code size and avoid + * any divide that could add a dependency on large external functions. */ static __attribute__((unused)) -const char *ltoa_r(long in, char *buffer) +int utoa_r(unsigned long in, char *buffer) { - char *pos = buffer + 21 - 1; - int neg = in < 0; - unsigned long n = neg ? -in : in; + unsigned long lim; + int digits = 0; + int pos = (~0UL > 0xfffffffful) ? 19 : 9; + int dig; - *pos-- = '\0'; do { - *pos-- = '0' + n % 10; - n /= 10; - if (pos < buffer) - return pos + 1; - } while (n); + for (dig = 0, lim = 1; dig < pos; dig++) + lim *= 10; - if (neg) - *pos-- = '-'; - return pos + 1; + if (digits || in >= lim || !pos) { + for (dig = 0; in >= lim; dig++) + in -= lim; + buffer[digits++] = '0' + dig; + } + } while (pos--); + + buffer[digits] = 0; + return digits; } -/* performs the opposite of atol() using a statically allocated buffer */ +/* Converts the signed long integer to its string representation into + * buffer , which must be long enough to store the number and the + * trailing zero (21 bytes for -9223372036854775808 in 64-bit, 12 for + * -2147483648 in 32-bit). The buffer is filled from the first byte, and the + * number of characters emitted (not counting the trailing zero) is returned. + */ static __attribute__((unused)) -const char *ltoa(long in) +int itoa_r(long in, char *buffer) { - /* large enough for -9223372036854775808 */ - static char buffer[21]; - return ltoa_r(in, buffer); + char *ptr = buffer; + int len = 0; + + if (in < 0) { + in = -in; + *(ptr++) = '-'; + len++; + } + len += utoa_r(in, ptr); + return len; +} + +/* for historical compatibility, same as above but returns the pointer to the + * buffer. + */ +static inline __attribute__((unused)) +char *ltoa_r(long in, char *buffer) +{ + itoa_r(in, buffer); + return buffer; +} + +/* converts long integer to a string using the static itoa_buffer and + * returns the pointer to that string. + */ +static inline __attribute__((unused)) +char *itoa(long in) +{ + itoa_r(in, itoa_buffer); + return itoa_buffer; +} + +/* converts long integer to a string using the static itoa_buffer and + * returns the pointer to that string. Same as above, for compatibility. + */ +static inline __attribute__((unused)) +char *ltoa(long in) +{ + itoa_r(in, itoa_buffer); + return itoa_buffer; +} + +/* converts unsigned long integer to a string using the static itoa_buffer + * and returns the pointer to that string. + */ +static inline __attribute__((unused)) +char *utoa(unsigned long in) +{ + utoa_r(in, itoa_buffer); + return itoa_buffer; } static __attribute__((unused)) -- 2.35.1