Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933348Ab2FIAu6 (ORCPT ); Fri, 8 Jun 2012 20:50:58 -0400 Received: from mail-pb0-f46.google.com ([209.85.160.46]:50988 "EHLO mail-pb0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932201Ab2FIAuz (ORCPT ); Fri, 8 Jun 2012 20:50:55 -0400 From: Akinobu Mita To: linux-kernel@vger.kernel.org, akpm@linux-foundation.org Cc: Akinobu Mita , Anders Larsen , Alasdair Kergon , dm-devel@redhat.com, linux-fsdevel@vger.kernel.org, Laurent Pinchart , linux-media@vger.kernel.org, Mark Fasheh , Joel Becker , ocfs2-devel@oss.oracle.com, Jan Kara , linux-ext4@vger.kernel.org, Andreas Dilger , "Theodore Ts'o" , Matthew Wilcox Subject: [PATCH v3 1/9] string: introduce memweight Date: Sat, 9 Jun 2012 09:50:30 +0900 Message-Id: <1339203038-13069-1-git-send-email-akinobu.mita@gmail.com> X-Mailer: git-send-email 1.7.7.6 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3118 Lines: 100 memweight() is the function that counts the total number of bits set in memory area. Unlike bitmap_weight(), memweight() takes pointer and size in bytes to specify a memory area which does not need to be aligned to long-word boundary. Signed-off-by: Akinobu Mita Cc: Anders Larsen Cc: Alasdair Kergon Cc: dm-devel@redhat.com Cc: linux-fsdevel@vger.kernel.org Cc: Laurent Pinchart Cc: linux-media@vger.kernel.org Cc: Mark Fasheh Cc: Joel Becker Cc: ocfs2-devel@oss.oracle.com Cc: Jan Kara Cc: linux-ext4@vger.kernel.org Cc: Andrew Morton Cc: Andreas Dilger Cc: "Theodore Ts'o" Cc: Matthew Wilcox --- v3: add comment for the last loop, adviced by Jan Kara v2: simplify memweight(), adviced by Jan Kara include/linux/string.h | 3 +++ lib/string.c | 36 ++++++++++++++++++++++++++++++++++++ 2 files changed, 39 insertions(+), 0 deletions(-) diff --git a/include/linux/string.h b/include/linux/string.h index e033564..ffe0442 100644 --- a/include/linux/string.h +++ b/include/linux/string.h @@ -145,4 +145,7 @@ static inline bool strstarts(const char *str, const char *prefix) return strncmp(str, prefix, strlen(prefix)) == 0; } #endif + +extern size_t memweight(const void *ptr, size_t bytes); + #endif /* _LINUX_STRING_H_ */ diff --git a/lib/string.c b/lib/string.c index e5878de..e467186 100644 --- a/lib/string.c +++ b/lib/string.c @@ -26,6 +26,7 @@ #include #include #include +#include #ifndef __HAVE_ARCH_STRNICMP /** @@ -824,3 +825,38 @@ void *memchr_inv(const void *start, int c, size_t bytes) return check_bytes8(start, value, bytes % 8); } EXPORT_SYMBOL(memchr_inv); + +/** + * memweight - count the total number of bits set in memory area + * @ptr: pointer to the start of the area + * @bytes: the size of the area + */ +size_t memweight(const void *ptr, size_t bytes) +{ + size_t w = 0; + size_t longs; + const unsigned char *bitmap = ptr; + + for (; bytes > 0 && ((unsigned long)bitmap) % sizeof(long); + bytes--, bitmap++) + w += hweight8(*bitmap); + + longs = bytes / sizeof(long); + if (longs) { + BUG_ON(longs >= INT_MAX / BITS_PER_LONG); + w += bitmap_weight((unsigned long *)bitmap, + longs * BITS_PER_LONG); + bytes -= longs * sizeof(long); + bitmap += longs * sizeof(long); + } + /* + * The reason that this last loop is distinct from the preceding + * bitmap_weight() call is to compute 1-bits in the last region smaller + * than sizeof(long) properly on big-endian systems. + */ + for (; bytes > 0; bytes--, bitmap++) + w += hweight8(*bitmap); + + return w; +} +EXPORT_SYMBOL(memweight); -- 1.7.7.6 -- 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/