[quagga-dev 16655] [PATCH] tests: Fix test-checksum to move the mod operation up

Athira Rajeev atrajeev at linux.vnet.ibm.com
Thu Aug 24 08:15:25 BST 2017


From: Athira Rajeev <atrajeev at linux.vnet.ibm.com <mailto:atrajeev at linux.vnet.ibm.com>>

testchecksum fails with "verify: isisd failed" for few iterations.
Checking the test code, it calls iso_csum_create followed by verify function
where it fails in some cases.

Code snippet:

isisd = iso_csum_create (buffer, exercise + sizeof(u_int16_t), exercise);
if (verify (buffer, exercise + sizeof(u_int16_t)))
 printf ("verify: isisd failed\n");

In iso_csum_create , code uses modulo ( % ) operation.
Code snippet:
 ========
 mul = (init_len - off) * c0;

 x = mul - c1 - c0;
 y = c1 - mul - 1;

 if (y > 0)
   y++;
 if (x < 0)
   x--;

 x %= 255;
 y %= 255;

 if (x == 0)
   x = 255;
 if (y == 0)
   y = 1;
 ========

Moved the modulus operation up the if condition in testcase and
isisd verify goes fine without reporting fail.
Referring this mail thread https://lists.gt.net/quagga/dev/17347 <https://lists.gt.net/quagga/dev/17347>
and https://github.com/Quagga/quagga/commit/5d4b8cf2faba9f5386810a7c70837e5b7fae3572#diff-5fb4cfc11e8bb396af1ce29581abfb89 <https://github.com/Quagga/quagga/commit/5d4b8cf2faba9f5386810a7c70837e5b7fae3572#diff-5fb4cfc11e8bb396af1ce29581abfb89> ,
mod operation was moved up for "reduce_isisd_mod" in past commits.

Also observed that without moving mod up and introducing sleep after mod operation also solves the issue :

--- test-checksum.c.org <http://test-checksum.c.org/>	2017-08-23 12:19:43.688263168 +0000
+++ test-checksum.c	2017-08-23 12:22:43.400260726 +0000
@@ -360,6 +360,8 @@ iso_csum_create (u_char * buffer, testsz
  x %= 255;
  y %= 255;

+  sleep(1);
+
  if (x == 0)
    x = 255;
  if (y == 0)

Reason behind this appears that modulus operator is slow.
Reference links:
https://stackoverflow.com/questions/27977834/why-is-modulus-operator-slow <https://stackoverflow.com/questions/27977834/why-is-modulus-operator-slow>

But Since "Moving the mod up" was followed as solution in past commits, adding that patch here.

Signed-off-by: Athira Rajeev <atrajeev at linux.vnet.ibm.com <mailto:atrajeev at linux.vnet.ibm.com>>
---
tests/test-checksum.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/tests/test-checksum.c b/tests/test-checksum.c
index b6741f30..99d255ef 100644
--- a/tests/test-checksum.c
+++ b/tests/test-checksum.c
@@ -352,14 +352,14 @@ iso_csum_create (u_char * buffer, testsz_t len, testoff_t off)
  x = mul - c1 - c0;
  y = c1 - mul - 1;

+  x %= 255;
+  y %= 255;
+
  if (y > 0)
    y++;
  if (x < 0)
    x--;

-  x %= 255;
-  y %= 255;
-
  if (x == 0)
    x = 255;
  if (y == 0)
-- 
2.11.0 (Apple Git-81)
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