better doc for return values.


git-svn-id: http://svn.xiph.org/trunk/speex@12770 0101bb08-14d6-0310-b084-bc0e0c8e3800
diff --git a/include/speex/speex.h b/include/speex/speex.h
index 0f8d732..f17fa19 100644
--- a/include/speex/speex.h
+++ b/include/speex/speex.h
@@ -297,7 +297,7 @@
  * encode, you need one state per channel.
  *
  * @param mode The mode to use (either speex_nb_mode or speex_wb.mode) 
- * @return A newly created encoder
+ * @return A newly created encoder state or NULL if state allocation fails
  */
 void *speex_encoder_init(const SpeexMode *mode);
 
@@ -330,7 +330,7 @@
  * @param state Encoder state
  * @param request ioctl-type request (one of the SPEEX_* macros)
  * @param ptr Data exchanged to-from function
- * @return 0 if no error, -1 if request in unknown
+ * @return 0 if no error, -1 if request in unknown, -2 for invalid parameter
  */
 int speex_encoder_ctl(void *state, int request, void *ptr);
 
@@ -341,7 +341,7 @@
  * decode, you need one state per channel.
  *
  * @param mode Speex mode (one of speex_nb_mode or speex_wb_mode)
- * @return A newly created decoder state
+ * @return A newly created decoder state or NULL if state allocation fails
  */ 
 void *speex_decoder_init(const SpeexMode *mode);
 
@@ -376,7 +376,7 @@
  * @param state Decoder state
  * @param request ioctl-type request (one of the SPEEX_* macros)
  * @param ptr Data exchanged to-from function
- * @return 0 if no error, -1 if request in unknown
+ * @return 0 if no error, -1 if request in unknown, -2 for invalid parameter
  */
 int speex_decoder_ctl(void *state, int request, void *ptr);
 
@@ -386,12 +386,14 @@
  * @param mode Speex mode
  * @param request ioctl-type request (one of the SPEEX_* macros)
  * @param ptr Data exchanged to-from function
+ * @return 0 if no error, -1 if request in unknown, -2 for invalid parameter
  */
 int speex_mode_query(const SpeexMode *mode, int request, void *ptr);
 
 /** Functions for controlling the behavior of libspeex
  * @param request ioctl-type request (one of the SPEEX_LIB_* macros)
  * @param ptr Data exchanged to-from function
+ * @return 0 if no error, -1 if request in unknown, -2 for invalid parameter
  */
 int speex_lib_ctl(int request, void *ptr);