MP3Decoder: clear out DSP data when opening a new stream

The new test verifies that the first part of an MP3 decodes as
expected even when the "open" method is used.

Closes: #9705

shared-module/audiomp3/MP3Decoder.c

@@ -20,6 +20,7 @@
 #include "shared-module/audiomp3/MP3Decoder.h"
 #include "supervisor/background_callback.h"
 #include "lib/mp3/src/mp3common.h"
+#include "lib/mp3/src/coder.h"
 
 #define MAX_BUFFER_LEN (MAX_NSAMP * MAX_NGRAN * MAX_NCHAN * sizeof(int16_t))
 
@@ -360,6 +361,17 @@ void common_hal_audiomp3_mp3file_set_file(audiomp3_mp3file_obj_t *self, mp_obj_t
     // get_buffer() that I didn't understand.
     memset(self->pcm_buffer[0], 0, MAX_BUFFER_LEN);
     memset(self->pcm_buffer[1], 0, MAX_BUFFER_LEN);
+
+    /* important to do this - DSP primitives assume a bunch of state variables are 0 on first use */
+    struct _MP3DecInfo *decoder = self->decoder;
+    memset(decoder->FrameHeaderPS, 0, sizeof(FrameHeader));
+    memset(decoder->SideInfoPS, 0, sizeof(SideInfo));
+    memset(decoder->ScaleFactorInfoPS, 0, sizeof(ScaleFactorInfo));
+    memset(decoder->HuffmanInfoPS, 0, sizeof(HuffmanInfo));
+    memset(decoder->DequantInfoPS, 0, sizeof(DequantInfo));
+    memset(decoder->IMDCTInfoPS, 0, sizeof(IMDCTInfo));
+    memset(decoder->SubbandInfoPS, 0, sizeof(SubbandInfo));
+
     MP3FrameInfo fi;
     bool result = mp3file_get_next_frame_info(self, &fi, true);
     background_callback_allow();

tests/circuitpython/issue9705.py

@@ -0,0 +1,30 @@
+import audiomp3, audiocore
+import ulab.numpy as np
+
+TEST_FILE = __file__.rsplit("/", 1)[0] + "/../circuitpython-manual/audiocore/jeplayer-splash-44100-stereo.mp3"
+
+def normalized_rms_ulab(values):
+    values = np.frombuffer(values, dtype=np.int16)
+    # this function works with ndarrays only
+    minbuf = np.mean(values)
+    values = values - minbuf
+    samples_sum = np.sum(values * values)
+    return (samples_sum / len(values))**.5
+
+def print_frame_loudness(decoder, n):
+    for i in range(n):
+        result, buf = audiocore.get_buffer(decoder)
+        print(f"{i} {result} {normalized_rms_ulab(buf):5.0f}")
+    print()
+
+# First frames
+decoder = audiomp3.MP3Decoder(TEST_FILE)
+print_frame_loudness(decoder, 8)
+
+# First frames (fresh decoder)
+decoder = audiomp3.MP3Decoder(TEST_FILE)
+print_frame_loudness(decoder, 2)
+
+# First frames (reopen)
+decoder.open(TEST_FILE)
+print_frame_loudness(decoder, 3)

tests/circuitpython/issue9705.py.exp

@@ -0,0 +1,16 @@
+0 1     0
+1 1  4730
+2 1 27914
+3 1 28737
+4 1 29251
+5 1 29219
+6 1 28672
+7 1 28213
+
+0 1     0
+1 1  4730
+
+0 1     0
+1 1  4730
+2 1 27914
+