Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753987AbbKBWsy (ORCPT ); Mon, 2 Nov 2015 17:48:54 -0500 Received: from relais.videotron.ca ([24.201.245.36]:41140 "EHLO relais.videotron.ca" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753529AbbKBWsq (ORCPT ); Mon, 2 Nov 2015 17:48:46 -0500 Content-transfer-encoding: 7BIT From: Nicolas Pitre To: Alexey Brodkin , =?UTF-8?q?M=C3=A5ns=20Rullg=C3=A5rd?= Cc: Arnd Bergmann , rmk+kernel@arm.linux.org.uk, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH 1/5] div64.h: optimize do_div() for power-of-two constant divisors Date: Mon, 02 Nov 2015 17:33:26 -0500 Message-id: <1446503610-6942-2-git-send-email-nicolas.pitre@linaro.org> X-Mailer: git-send-email 2.4.3 In-reply-to: <1446503610-6942-1-git-send-email-nicolas.pitre@linaro.org> References: <1446503610-6942-1-git-send-email-nicolas.pitre@linaro.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1286 Lines: 35 On 32-bit targets, gcc is able to do the right thing with a constant divisor that happens to be a power of two i.e. it turns the division into a right shift inline. Signed-off-by: Nicolas Pitre --- include/asm-generic/div64.h | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/include/asm-generic/div64.h b/include/asm-generic/div64.h index 8f4e319334..47aa1e2134 100644 --- a/include/asm-generic/div64.h +++ b/include/asm-generic/div64.h @@ -41,7 +41,12 @@ extern uint32_t __div64_32(uint64_t *dividend, uint32_t divisor); uint32_t __base = (base); \ uint32_t __rem; \ (void)(((typeof((n)) *)0) == ((uint64_t *)0)); \ - if (likely(((n) >> 32) == 0)) { \ + if (__builtin_constant_p(__base) && \ + (__base & (__base - 1)) == 0) { \ + /* constant power of 2: gcc is fine */ \ + __rem = (n) & (__base - 1); \ + (n) /= __base; \ + } else if (likely(((n) >> 32) == 0)) { \ __rem = (uint32_t)(n) % __base; \ (n) = (uint32_t)(n) / __base; \ } else \ -- 2.4.3 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/