libtwamr encoder: always emit frame->mode = mode; In the original implementation of amr_encode_frame(), the 'mode' member of the output struct was set to 0xFF if the output frame type is TX_NO_DATA. This design was made to mimic the mode field (16-bit word) being set to 0xFFFF (or -1) in 3GPP test sequence format - but nothing actually depends on this struct member being set in any way, and amr_frame_to_tseq() generates the needed 0xFFFF on its own, based on frame->type being equal to TX_NO_DATA. It is simpler and more efficient to always set frame->mode to the actual encoding mode in amr_encode_frame(), and this new behavior has already been documented in doc/AMR-library-API description in anticipation of the present change.

/*-----------------------------------------------------------------------*
 *  Scalar quantization tables of the pitch gain and the codebook gain.  *
 *-----------------------------------------------------------------------*/

#define NB_QUA_PITCH 16

static const Word16 qua_gain_pitch[NB_QUA_PITCH] =
{
    0, 3277, 6556, 8192, 9830, 11469, 12288, 13107,
    13926, 14746, 15565, 16384, 17203, 18022, 18842, 19661
};

#define NB_QUA_CODE 32

static const Word16 qua_gain_code[NB_QUA_CODE] =
{
    159, 206, 268, 349, 419, 482, 554, 637,
    733, 842, 969, 1114, 1281, 1473, 1694, 1948,
    2241, 2577, 2963, 3408, 3919, 4507, 5183, 5960,
    6855, 7883, 9065, 10425, 12510, 16263, 21142, 27485
};