Fix the side frame conditional coding rules.

b24e5746 introduced changes to LastGainIndex which broke
 conditional coding for side frames after a mid-only frame (i.e.,
 in a 60 ms frame where the side is coded, not coded, then coded
 again).
These rules were a mess in general, however, because the side
 channel state kept a different nFramesDecoded count from the mid
 channel state, and had no way to tell if the prior side frame was
 coded.

This patch attempts to rationalize them by moving the conditional
 coding decision up to the top level, where all this information is
 available.
The first coded side frame after an uncoded side frame now always
 uses independent coding.
If such a frame is also not the first side frame in an Opus frame,
 then it doesn't include an LTP scaling parameter (because the LTP
 state is well-defined).

1 files changed, 6 insertions, 12 deletions

diff --git a/silk/decode_indices.c b/silk/decode_indices.c
index 9ea0a80e..8ac53f4b 100644
--- a/silk/decode_indices.c
+++ b/silk/decode_indices.c
@@ -36,21 +36,15 @@ void silk_decode_indices(
     silk_decoder_state      *psDec,             /* I/O  State                                       */
     ec_dec                      *psRangeDec,        /* I/O  Compressor data structure                   */
     opus_int                     FrameIndex,         /* I    Frame number                                */
-    opus_int                     decode_LBRR         /* I    Flag indicating LBRR data is being decoded  */
+    opus_int                     decode_LBRR,        /* I    Flag indicating LBRR data is being decoded  */
+    opus_int                     condCoding          /* I    The type of conditional coding to use       */
 )
 {
-    opus_int   i, k, Ix, condCoding;
+    opus_int   i, k, Ix;
     opus_int   decode_absolute_lagIndex, delta_lagIndex;
     opus_int16 ec_ix[ MAX_LPC_ORDER ];
     opus_uint8 pred_Q8[ MAX_LPC_ORDER ];
 
-    /* Use conditional coding if previous frame available */
-    if( FrameIndex > 0 && ( decode_LBRR == 0 || psDec->LBRR_flags[ FrameIndex - 1 ] == 1 ) ) {
-        condCoding = 1;
-    } else {
-        condCoding = 0;
-    }
-
     /*******************************************/
     /* Decode signal type and quantizer offset */
     /*******************************************/
@@ -66,7 +60,7 @@ void silk_decode_indices(
     /* Decode gains */
     /****************/
     /* First subframe */
-    if( condCoding ) {
+    if( condCoding == CODE_CONDITIONALLY ) {
         /* Conditional coding */
         psDec->indices.GainsIndices[ 0 ] = (opus_int8)ec_dec_icdf( psRangeDec, silk_delta_gain_iCDF, 8 );
     } else {
@@ -110,7 +104,7 @@ void silk_decode_indices(
         /*********************/
         /* Get lag index */
         decode_absolute_lagIndex = 1;
-        if( condCoding && psDec->ec_prevSignalType == TYPE_VOICED ) {
+        if( condCoding == CODE_CONDITIONALLY && psDec->ec_prevSignalType == TYPE_VOICED ) {
             /* Decode Delta index */
             delta_lagIndex = (opus_int16)ec_dec_icdf( psRangeDec, silk_pitch_delta_iCDF, 8 );
             if( delta_lagIndex > 0 ) {
@@ -142,7 +136,7 @@ void silk_decode_indices(
         /**********************/
         /* Decode LTP scaling */
         /**********************/
-        if( !condCoding ) {
+        if( condCoding == CODE_INDEPENDENTLY ) {
             psDec->indices.LTP_scaleIndex = (opus_int8)ec_dec_icdf( psRangeDec, silk_LTPscale_iCDF, 8 );
         } else {
             psDec->indices.LTP_scaleIndex = 0;