DataFlash: avoid integer underflow

Thanks to mbelluzzo: f44b1b3556
2016-09-13 12:32:01 +10:00 · 2016-09-13 12:32:01 +10:00 · fce798bc7a
parent 95d4475d45
commit fce798bc7a
1 changed files with 4 additions and 1 deletions
--- a/libraries/DataFlash/DataFlash_File.cpp
+++ b/libraries/DataFlash/DataFlash_File.cpp
@ -207,7 +207,10 @@ void DataFlash_File::periodic_fullrate(const uint32_t now)
 uint16_t DataFlash_File::bufferspace_available()
 {
    uint16_t _head;
-    return (BUF_SPACE(_writebuf)) - critical_message_reserved_space();
+    const uint16_t space = BUF_SPACE(_writebuf);
+    const uint16_t crit = critical_message_reserved_space();
+
+    return (space > crit) ? space - crit : 0;
 }

 // return true for CardInserted() if we successfully initialised