multipath: Correctly calculate number of required destination bits.

The previous calculation was wrong when n_links was a power of 2.

Reported-by: Paul Ingram <paul@nicira.com>
Signed-off-by: Ben Pfaff <blp@nicira.com>

diff --git a/lib/multipath.c b/lib/multipath.c
index f68dafd..adc000d 100644 (file)
--- a/lib/multipath.c
+++ b/lib/multipath.c
@@ -37,7 +37,7 @@ int
 multipath_check(const struct nx_action_multipath *mp, const struct flow *flow)
 {
     uint32_t n_links = ntohs(mp->max_link) + 1;
-    size_t min_n_bits = log_2_floor(n_links) + 1;
+    size_t min_n_bits = log_2_ceil(n_links);
     int ofs = nxm_decode_ofs(mp->ofs_nbits);
     int n_bits = nxm_decode_n_bits(mp->ofs_nbits);
     int error;

diff --git a/lib/util.c b/lib/util.c
index e02f59f..8379c9a 100644 (file)
--- a/lib/util.c
+++ b/lib/util.c
@@ -664,6 +664,14 @@ log_2_floor(uint32_t n)
 #endif
 }
 
+/* Given a 32 bit word 'n', calculates ceil(log_2('n')).  It is an error to
+ * call this function with 'n' == 0. */
+int
+log_2_ceil(uint32_t n)
+{
+    return log_2_floor(n) + !IS_POW2(n);
+}
+
 /* Returns the number of trailing 0-bits in 'n', or 32 if 'n' is 0. */
 int
 ctz(uint32_t n)

diff --git a/lib/util.h b/lib/util.h
index 61039be..b2052f3 100644 (file)
--- a/lib/util.h
+++ b/lib/util.h
@@ -203,6 +203,7 @@ char *abs_file_name(const char *dir, const char *file_name);
 
 void ignore(bool x OVS_UNUSED);
 int log_2_floor(uint32_t);
+int log_2_ceil(uint32_t);
 int ctz(uint32_t);
 
 bool is_all_zeros(const uint8_t *, size_t);