diff --git a/libavcodec/g729data.h b/libavcodec/g729data.h
index 05b40416dd..f0a09ab14c 100644
--- a/libavcodec/g729data.h
+++ b/libavcodec/g729data.h
@@ -293,6 +293,15 @@ static const int16_t cb_ma_predictor_sum[2][10] = { /* (0.15) */
   {14585, 18333, 19772, 17344, 16426, 16459, 15155, 15220, 16043, 15708}
 };
 
+/**
+ *                                                           12
+ *                                                          2
+ * cb_ma_predictor_sum_inv[j][i] = floor(---------------------------------------------)
+ *                                               3
+ *                                        1.0 - sum ( cb_ma_predictor_float[j][k][i] )
+ *                                              k=0
+ * j=0..1, i=0..9
+ */
 static const int16_t cb_ma_predictor_sum_inv[2][10] = { /* (3.12) */
   {17210, 15888, 16357, 16183, 16516, 15833, 15888, 15421, 14840, 15597},
   { 9202,  7320,  6788,  7738,  8170,  8154,  8856,  8818,  8366,  8544}
diff --git a/libavcodec/g729dec.c b/libavcodec/g729dec.c
index b8dba4282f..42783d61fb 100644
--- a/libavcodec/g729dec.c
+++ b/libavcodec/g729dec.c
@@ -171,6 +171,13 @@ static void lsf_decode(int16_t* lsfq, int16_t* past_quantizer_outputs[MA_NP + 1]
     ff_acelp_reorder_lsf(lsfq, LSFQ_DIFF_MIN, LSFQ_MIN, LSFQ_MAX, 10);
 }
 
+/**
+ * Restores past LSP quantizer output using LSF from previous frame
+ * @param lsfq [in/out] (2.13) quantized LSF coefficients
+ * @param past_quantizer_outputs [in/out] (2.13) quantizer outputs from previous frames
+ * @param ma_predictor_prev MA predictor from previous frame
+ * @param lsfq_prev (2.13) quantized LSF coefficients from previous frame
+ */
 static void lsf_restore_from_previous(int16_t* lsfq,
                                       int16_t* past_quantizer_outputs[MA_NP + 1],
                                       int ma_predictor_prev)