From mboxrd@z Thu Jan 1 00:00:00 1970 From: Przemyslaw Iskra Date: Fri, 30 Jul 2010 19:05:35 +0200 Subject: [PATCH] Don't use floor() in _bitset_with_random_bits Message-ID: <20100730170535.GA21519@pld-linux.org> List-Id: To: lvm-devel@redhat.com MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Use _even_rand() function instead of floor() in _bitset_with_random_bits(). floor() function is missing in dietlibc (on architectures other than x86). Moreover using floor() to clip rand results does not assure even result distribution. _even_rand() uses integer arithmetic only and is designed to return evenly distributed results. Signed-off-by: Przemyslaw Iskra --- configure.in | 3 +-- lib/metadata/metadata.c | 16 +++++++++++++++- 2 files changed, 16 insertions(+), 3 deletions(-) diff --git a/configure.in b/configure.in index bd56136..6f6c67e 100644 --- a/configure.in +++ b/configure.in @@ -125,8 +125,7 @@ AC_STRUCT_TM ################################################################################ dnl -- Check for functions -AC_SEARCH_LIBS([floor], [m], , [AC_MSG_ERROR(bailing out)]) -AC_CHECK_FUNCS([floor ftruncate gethostname getpagesize \ +AC_CHECK_FUNCS([ftruncate gethostname getpagesize \ gettimeofday memset mkdir mkfifo rmdir munmap nl_langinfo setenv setlocale \ strcasecmp strchr strcspn strspn strdup strncasecmp strerror strrchr \ strstr strtol strtoul uname], , [AC_MSG_ERROR(bailing out)]) diff --git a/lib/metadata/metadata.c b/lib/metadata/metadata.c index 07222a7..6ee7731 100644 --- a/lib/metadata/metadata.c +++ b/lib/metadata/metadata.c @@ -1018,6 +1018,20 @@ static int _recalc_extents(uint32_t *extents, const char *desc1, return 1; } +/* return random integer in [0,max) interval */ +static unsigned _even_rand( unsigned *seed, unsigned max ) +{ + unsigned r, ret; + + /* make sure distribution is even */ + do { + r = (unsigned) rand_r( seed ); + ret = r % max; + } while ( r - ret >= RAND_MAX - max ); + + return ret; +} + static dm_bitset_t _bitset_with_random_bits(struct dm_pool *mem, uint32_t num_bits, uint32_t num_set_bits, unsigned *seed) { @@ -1040,7 +1054,7 @@ static dm_bitset_t _bitset_with_random_bits(struct dm_pool *mem, uint32_t num_bi /* Perform loop num_set_bits times, selecting one bit each time */ while (i++ < num_bits) { /* Select a random bit between 0 and (i-1) inclusive. */ - bit_selected = (unsigned) floor(i * (rand_r(seed) / (RAND_MAX + 1.0))); + bit_selected = _even_rand( seed, i ); /* * If the bit was already set, set the new bit that became -- 1.7.1 -- ____ Sparky{PI] -- Przemyslaw _ ___ _ _ ......... LANG...Pl,Ca,Es,En /____) ___ ___ _ _ || Iskra | | _ \| | | : WWW...ppcrcd.pld-linux.org \____\| -_)'___| ||^'||//\\// < | _/| | | : WWW2..............rsget.pl (____/|| (_-_|_|| ||\\ || |_ |_| |_| _| : Mail..sparky@pld-linux.org