Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755468AbdLTOUY (ORCPT ); Wed, 20 Dec 2017 09:20:24 -0500 Received: from mail-lf0-f66.google.com ([209.85.215.66]:38269 "EHLO mail-lf0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755317AbdLTOUU (ORCPT ); Wed, 20 Dec 2017 09:20:20 -0500 X-Google-Smtp-Source: ACJfBosGxcaKduwLTgprLGO/8iiyDNLR3+kWmazbg9junHbNaqbG1vm7/j6vfQePiKfBtckI71EQhygGxuQ2WtM/cLU= MIME-Version: 1.0 In-Reply-To: <1513763787.1234.102.camel@perches.com> References: <20171220093315.25311-1-cmo@melexis.com> <1513763787.1234.102.camel@perches.com> From: Crt Mori Date: Wed, 20 Dec 2017 15:19:38 +0100 Message-ID: Subject: Re: [PATCH v9 1/3] lib: Add strongly typed 64bit int_sqrt To: Joe Perches Cc: Jonathan Cameron , Ingo Molnar , Andrew Morton , Kees Cook , Rusty Russell , Ian Abbott , Larry Finger , Niklas Soderlund , Thomas Gleixner , Krzysztof Kozlowski , Masahiro Yamada , linux-kernel@vger.kernel.org, Linux Iio , Peter Zijlstra Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1740 Lines: 70 On 20 December 2017 at 10:56, Joe Perches wrote: > On Wed, 2017-12-20 at 10:33 +0100, Crt Mori wrote: >> There is no option to perform 64bit integer sqrt on 32bit platform. >> Added stronger typed int_sqrt64 enables the 64bit calculations to >> be performed on 32bit platforms. Although int_sqrt() is a rough >> approximation, the same algorithm is used in int_sqrt64() as good >> enough on 32bit platform. > [] >> diff --git a/include/linux/kernel.h b/include/linux/kernel.h > [] >> @@ -459,6 +459,7 @@ extern int kernel_text_address(unsigned long addr); >> extern int func_ptr_is_kernel_text(void *ptr); >> >> unsigned long int_sqrt(unsigned long); >> +u32 int_sqrt64(u64 x); > > #ifdef BITS_PER_LONG == 64 > static inline u32 int_sqrt64(u64 x) > { > re > turn (u32)int_sqrt(x); > } > #else > u32 int_sqrt64(u64 x); > #endif > > [] > OK, fixing it in v10. >> +#if BITS_PER_LONG < 64 >> +/** >> + * int_sqrt64 - strongly typed int_sqrt function when minimum 64 bit input >> + * is expected. >> + * @x: 64bit integer of which to calculate the sqrt >> + */ >> +u32 int_sqrt64(u64 x) >> +{ >> + u64 b, m, y = 0; >> + >> + if (x <= 1) >> + return x; >> + >> + m = 1ULL << (fls64(x) & ~1ULL); >> + while (m != 0) { >> + b = y + m; >> + y >>= 1; >> + >> + if (x >= b) { >> + x -= b; >> + y += m; >> + } >> + m >>= 2; >> + } >> + >> + return y; >> +} >> +EXPORT_SYMBOL(int_sqrt64); >> +#else >> +u32 int_sqrt64(u64 x) >> +{ >> + return int_sqrt(x); >> +} >> +EXPORT_SYMBOL(int_sqrt64); >> +#endif > > This doesn't need to be EXPORT_SYMBOL for the > BITS_PER_LONG == 64 case >