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[80.182.89.242]) by smtp.gmail.com with ESMTPSA id c3sm1290189edy.0.2021.07.02.05.32.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 02 Jul 2021 05:32:20 -0700 (PDT) From: Matteo Croce To: linux-kernel@vger.kernel.org, Nick Kossifidis , Guo Ren , Christoph Hellwig , David Laight , Palmer Dabbelt , Emil Renner Berthing , Drew Fustini Cc: linux-arch@vger.kernel.org, Andrew Morton , Nick Desaulniers , linux-riscv@lists.infradead.org Subject: [PATCH v2 2/3] lib/string: optimized memmove Date: Fri, 2 Jul 2021 14:31:52 +0200 Message-Id: <20210702123153.14093-3-mcroce@linux.microsoft.com> X-Mailer: git-send-email 2.31.1 In-Reply-To: <20210702123153.14093-1-mcroce@linux.microsoft.com> References: <20210702123153.14093-1-mcroce@linux.microsoft.com> MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210702_053221_877771_F2797F94 X-CRM114-Status: GOOD ( 13.50 ) X-BeenThere: linux-riscv@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-riscv" Errors-To: linux-riscv-bounces+linux-riscv=archiver.kernel.org@lists.infradead.org From: Matteo Croce When the destination buffer is before the source one, or when the buffers doesn't overlap, it's safe to use memcpy() instead, which is optimized to use a bigger data size possible. This "optimization" only covers a common case. In future, proper code which does the same thing as memcpy() does but backwards can be done. Signed-off-by: Matteo Croce --- lib/string.c | 18 ++++++------------ 1 file changed, 6 insertions(+), 12 deletions(-) diff --git a/lib/string.c b/lib/string.c index caeef4264c43..108b83c34cec 100644 --- a/lib/string.c +++ b/lib/string.c @@ -975,19 +975,13 @@ EXPORT_SYMBOL(memcpy); */ void *memmove(void *dest, const void *src, size_t count) { - char *tmp; - const char *s; + if (dest < src || src + count <= dest) + return memcpy(dest, src, count); + + if (dest > src) { + const char *s = src + count; + char *tmp = dest + count; - if (dest <= src) { - tmp = dest; - s = src; - while (count--) - *tmp++ = *s++; - } else { - tmp = dest; - tmp += count; - s = src; - s += count; while (count--) *--tmp = *--s; }