Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752924AbdLLXtD (ORCPT ); Tue, 12 Dec 2017 18:49:03 -0500 Received: from zeniv.linux.org.uk ([195.92.253.2]:38736 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752887AbdLLXs7 (ORCPT ); Tue, 12 Dec 2017 18:48:59 -0500 Date: Tue, 12 Dec 2017 23:48:56 +0000 From: Al Viro To: Jakub Kicinski Cc: Linus Torvalds , netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [RFC][PATCH] new byteorder primitives - ..._{replace,get}_bits() Message-ID: <20171212234856.GZ21978@ZenIV.linux.org.uk> References: <20171210045326.GO21978@ZenIV.linux.org.uk> <420a198d-61f8-81cf-646d-10446cb41def@synopsys.com> <20171211050520.GV21978@ZenIV.linux.org.uk> <20171211053803.GW21978@ZenIV.linux.org.uk> <20171211155422.GA12326@ZenIV.linux.org.uk> <20171211200224.23bc5df4@cakuba.netronome.com> <20171212062002.GY21978@ZenIV.linux.org.uk> <20171212194532.GA7062@ZenIV.linux.org.uk> <20171212120409.64b6362e@cakuba.netronome.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171212120409.64b6362e@cakuba.netronome.com> User-Agent: Mutt/1.9.0 (2017-09-02) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2175 Lines: 64 On Tue, Dec 12, 2017 at 12:04:09PM -0800, Jakub Kicinski wrote: > > static __always_inline u64 mask_to_multiplier(u64 mask) > > { > > return mask & (mask ^ (mask - 1)); > > } D'oh. Even simpler than that, of course - static __always_inline u64 mask_to_multiplier(u64 mask) { return mask & -mask; } > Very nice! The compilation-time check if the value can fit in a field > covered by the mask (if they're both known) did help me catch bugs > early a few times over the years, so if it could be preserved we can > maybe even drop the FIELD_* macros and just use this approach? Umm... Something like this, perhaps? Same bunch, plus u{16,32,64}_... variants for host-endian. Adding sanity check on mask is also not hard, but I don't know how useful it actually is... diff --git a/include/linux/byteorder/generic.h b/include/linux/byteorder/generic.h index 451aaa0786ae..a032de9aa03d 100644 --- a/include/linux/byteorder/generic.h +++ b/include/linux/byteorder/generic.h @@ -187,4 +187,36 @@ static inline void be32_to_cpu_array(u32 *dst, const __be32 *src, size_t len) dst[i] = be32_to_cpu(src[i]); } +extern void __compiletime_error("value doesn't fit into mask") +__field_overflow(void); +static __always_inline u64 mask_to_multiplier(u64 mask) +{ + return mask & -mask; +} + +#define ____MAKE_OP(type,base,to,from) \ +static __always_inline __##type type##_replace_bits(__##type old, \ + base val, base mask) \ +{ \ + __##type m = to(mask); \ + if (__builtin_constant_p(val) && \ + (val & ~(mask/mask_to_multiplier(mask)))) \ + __field_overflow(); \ + return (old & ~m) | \ + (to(val * mask_to_multiplier(mask)) & m); \ +} \ +static __always_inline base type##_get_bits(__##type v, base mask) \ +{ \ + return (from(v) & mask)/mask_to_multiplier(mask); \ +} +#define __MAKE_OP(size) \ + ____MAKE_OP(le##size,u##size,cpu_to_le##size,le##size##_to_cpu) \ + ____MAKE_OP(be##size,u##size,cpu_to_be##size,be##size##_to_cpu) \ + ____MAKE_OP(u##size,u##size,,) +__MAKE_OP(16) +__MAKE_OP(32) +__MAKE_OP(64) +#undef __MAKE_OP +#undef ____MAKE_OP + #endif /* _LINUX_BYTEORDER_GENERIC_H */