nse/client: Allow NaN as standard deviation.

See <https://bugs.gnunet.org/view.php?id=7021#c18399>.

* doc/scheme-gnunet.tm
  (Estimation of the size of the network)[estimate:standard-deviation]:
  Document it.

2 files changed, 17 insertions, 7 deletions

diff --git a/doc/scheme-gnunet.tm b/doc/scheme-gnunet.tm
index 83e0a0b..e504622 100644
--- a/doc/scheme-gnunet.tm
+++ b/doc/scheme-gnunet.tm
@@ -1047,10 +1047,15 @@
 
   <\explain>
     <scm|(estimate:standard-deviation <var|estimate>)>
-  </explain|The estimated standard deviation on the base-2 logarithm of
-  peers, calculated over the last 64 rounds, with the <math|<frac|N|N-1>>
-  correction.<space|1em>This is a positive flonum, possibly zero or
-  infinite.>
+  <|explain>
+    The estimated standard deviation on the base-2 logarithm of peers,
+    calculated over the last 64 rounds, with the <math|<frac|N|N-1>>
+    correction.<space|1em>This is a positive flonum, possibly zero or
+    infinite, or not-a-number (indicating division of zero by zero).
+
+    If the peer has been connected to the network for a while, the number is
+    expected to be finite and strictly positive.
+  </explain>
 
   Assuming the network size is stable and the errors on the logarithmic
   estimate are normally distributed, the procedure
diff --git a/gnu/gnunet/nse/client.scm b/gnu/gnunet/nse/client.scm
index 7b0c6dd..d240c28 100644
--- a/gnu/gnunet/nse/client.scm
+++ b/gnu/gnunet/nse/client.scm
@@ -36,7 +36,7 @@
           estimate)
   (import (only (rnrs base)
                 begin define quote lambda case values expt = else apply
-                and >=)
+                and >= let or nan?)
           (only (rnrs control)
                 when unless)
           (only (rnrs records syntactic)
@@ -104,7 +104,7 @@ in @var{estimate} as a positive flonum (possibly zero or infinite)."
     (define (estimate:standard-deviation estimate)
       "Return the standard deviation of the logarithmic estimate
 of the number of peers of the last 64 rounds as a positive flonum
-(possibly zero or infinite)."
+(possibly zero or infinite), or not-a-number."
       (%estimate:standard-deviation estimate))
 
     (define (estimate:number-peers estimate)
@@ -147,7 +147,12 @@ even if not connected.  This is an idempotent operation."
                    (sizeof /:msg:nse:estimate '()))
                 ;; XXX: these two lines below are not tested
                 (>= (read% /:msg:nse:estimate '(size-estimate) slice) 0)
-                (>= (read% /:msg:nse:estimate '(std-deviation) slice) 0)))
+                ;; See <https://bugs.gnunet.org/view.php?id=7021#c18399> for
+                ;; situations in which the deviation can be infinite or NaN.
+                (let ((stddev
+                       (read% /:msg:nse:estimate '(std-deviation) slice)))
+                  (or (>= stddev 0)
+                      (nan? stddev)))))
           ((handle! slice) (handle-estimate! slice)))))
       (define (send-start!)
         ;; The service only starts sending estimates once