exchange

commit 81a90052b068dfbbe25cf4a0c8c60ca7bd274628
parent 4a72063112931a95520b81e157209bdf82b7e95d
Author: Christian Grothoff <christian@grothoff.org>
Date:   Mon, 12 Oct 2026 23:59:25 +0200

prevent log(neg) on exchange returning strange values

Diffstat:
M
src/lib/exchange_api_stefan.c
 | 
14
++++++++++++++

1 file changed, 14 insertions(+), 0 deletions(-)
diff --git a/src/lib/exchange_api_stefan.c b/src/lib/exchange_api_stefan.c
@@ -149,9 +149,23 @@ TALER_EXCHANGE_keys_stefan_b2n (
     return GNUNET_SYSERR;
   }
   min_d = amount_to_double (min);
+  if (min_d <= 0.0)
+  {
+    /* smallest denomination must have a positive value,
+       otherwise the logarithm below is undefined */
+    GNUNET_break_op (0);
+    return GNUNET_SYSERR;
+  }
   fee_d = abs_d
           + log_d * log2 (bru_d / min_d)
           + lin_d * bru_d;
+  if (fee_d < 0.0)
+  {
+    /* log2() is negative for gross amounts below the smallest
+       denomination; a fee is never negative, and without this
+       clamp the net amount would exceed the gross amount */
+    fee_d = 0.0;
+  }
   if (fee_d > bru_d)
   {
     GNUNET_assert (GNUNET_OK ==