[gnoduino] Revert "Match return value to type in available()"

[Lucian Langa <lucilanga src gnome org>]

commit 7e6cb2a19fb43fb41fa65ad886bbb2795f319903
Author: Cristian Maglie <c maglie bug st>
Date:   Tue Oct 21 17:18:26 2014 +0200

    Revert "Match return value to type in available()"
    
    This reverts commit f40e4713542fa862d5b99b256a642e001a796988.
    Added an hint for the buffer sizes.
    
    See #2057
    Fixes #2367

 hardware/arduino/cores/arduino/HardwareSerial.cpp |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)
---
diff --git a/hardware/arduino/cores/arduino/HardwareSerial.cpp 
b/hardware/arduino/cores/arduino/HardwareSerial.cpp
index 0d4928c..925b9a0 100644
--- a/hardware/arduino/cores/arduino/HardwareSerial.cpp
+++ b/hardware/arduino/cores/arduino/HardwareSerial.cpp
@@ -53,6 +53,8 @@
 // using a ring buffer (I think), in which head is the index of the location
 // to which to write the next incoming character and tail is the index of the
 // location from which to read.
+// NOTE: a "power of 2" buffer size is reccomended to dramatically
+//       optimize all the modulo operations for ring buffers.
 #if (RAMEND < 1000)
   #define SERIAL_BUFFER_SIZE 16
 #else
@@ -426,7 +428,7 @@ void HardwareSerial::end()
 
 int HardwareSerial::available(void)
 {
-  return (int)(SERIAL_BUFFER_SIZE + _rx_buffer->head - _rx_buffer->tail) % SERIAL_BUFFER_SIZE;
+  return ((unsigned int)(SERIAL_BUFFER_SIZE + _rx_buffer->head - _rx_buffer->tail)) % SERIAL_BUFFER_SIZE;
 }
 
 int HardwareSerial::peek(void)