- NEW; integer-only replacement for floor( rand( ) / N )

Changed files:
    lvm2-no-floor.patch -> 1.1

diff --git a/lvm2-no-floor.patch b/lvm2-no-floor.patch
new file mode 100644 (file)
index 0000000..d611a41
--- /dev/null
+++ b/lvm2-no-floor.patch
@@ -0,0 +1,69 @@
+From ab3a151bdae8566fddbd91cdc86c600083890f59 Mon Sep 17 00:00:00 2001
+From: Przemyslaw Iskra <sparky@pld-linux.org>
+Date: Fri, 30 Jul 2010 18:45:43 +0200
+Subject: [PATCH] Don't use floor() in _bitset_with_random_bits
+
+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 <sparky@pld-linux.org>
+---
+ 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
+