[mynewt-nimble] branch master updated: nimble/ll: Fix access address computation

[an...@apache.org]

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andk pushed a commit to branch master
in repository https://gitbox.apache.org/repos/asf/mynewt-nimble.git


The following commit(s) were added to refs/heads/master by this push:
     new ab8bc74  nimble/ll: Fix access address computation
ab8bc74 is described below

commit ab8bc74f92f71d79a3ae81687e0cbc37b681b567
Author: Andrzej Kaczmarek <an...@codecoup.pl>
AuthorDate: Tue Jan 22 12:41:29 2019 -0800

    nimble/ll: Fix access address computation
    
    Core 5.0, Vol 6, Part B, section 2.1.2:
        The Access Address shall be a 32-bit value. Each time it needs a
        new Access Address, the Link Layer shall generate a new random value
        that meets the following requirements:
          (...)
          * It shall have a minimum of two transitions in the most
            significant six bits.
    
    Current implementation of the above only checks if there are no
    transitions in 6 msb so it can create invalid access address.
    
    Transitions can be easily calculated using xor with the same value
    shifted - the result will have '1' at each position with transition so
    then it's just a matter of counting them.
---
 nimble/controller/src/ble_ll_conn.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/nimble/controller/src/ble_ll_conn.c b/nimble/controller/src/ble_ll_conn.c
index b6561a7..1efcf56 100644
--- a/nimble/controller/src/ble_ll_conn.c
+++ b/nimble/controller/src/ble_ll_conn.c
@@ -511,6 +511,7 @@ ble_ll_conn_calc_access_addr(void)
     uint8_t consecutive;
     uint8_t transitions;
     uint8_t ones;
+    int tmp;
 
     /* Calculate a random access address */
     aa = 0;
@@ -525,8 +526,8 @@ ble_ll_conn_calc_access_addr(void)
         }
 
         /* Upper 6 bits must have 2 transitions */
-        temp = aa_high & 0xFC00;
-        if ((temp == 0) || (temp == 0xFC00)) {
+        tmp = (int16_t)aa_high >> 10;
+        if (__builtin_popcount(tmp ^ (tmp >> 1)) < 2) {
             continue;
         }