cdiocddasrc: detect whether drive produces samples in non-host endianness

If drive produces samples in other endianness than the host,
we need to byte swap them before pushing them out, or we
produce nothing but noise. cdparanoia detects this automatically,
but libcdio does not, so we have to do it ourselves.

This is needed on e.g. the PowerBook G4 with Matshita UJ-816 drive.

https://bugzilla.gnome.org/show_bug.cgi?id=377280

ext/cdio/gstcdiocddasrc.c

@@ -85,6 +85,8 @@
 #include <string.h>
 #include <errno.h>
 
+#define SAMPLES_PER_SECTOR (CDIO_CD_FRAMESIZE_RAW / sizeof (gint16))
+
 #define DEFAULT_READ_SPEED   -1
 
 enum
@@ -179,6 +181,14 @@ gst_cdio_cdda_src_read_sector (GstAudioCdSrc * audiocdsrc, gint sector)
   if (cdio_read_audio_sector (src->cdio, data, sector) != 0)
     goto read_failed;
 
+  if (src->swap_le_be) {
+    gint16 *pcm_data = (gint16 *) data;
+    gint i;
+
+    for (i = 0; i < SAMPLES_PER_SECTOR; ++i)
+      pcm_data[i] = GUINT16_SWAP_LE_BE (pcm_data[i]);
+  }
+
   return gst_buffer_new_wrapped (data, CDIO_CD_FRAMESIZE_RAW);
 
   /* ERRORS */
@@ -194,6 +204,106 @@ read_failed:
   }
 }
 
+static gboolean
+gst_cdio_cdda_src_do_detect_drive_endianness (GstCdioCddaSrc * src, gint from,
+    gint to)
+{
+  gint16 pcm_data[SAMPLES_PER_SECTOR], last_pcm_ne, last_pcm_oe;
+  gdouble ne_sumd0, ne_sumd1, ne_factor;
+  gdouble oe_sumd0, oe_sumd1, oe_factor;
+  gdouble diff;
+  gint sector;
+  gint i;
+
+  ne_sumd0 = ne_sumd1 = 0.0;
+  oe_sumd0 = oe_sumd1 = 0.0;
+  last_pcm_ne = 0;
+  last_pcm_oe = 0;
+
+  GST_LOG_OBJECT (src, "checking sector %d to %d", from, to);
+
+  for (sector = from; sector < to; ++sector) {
+    if (cdio_read_audio_sector (src->cdio, pcm_data, sector) != 0)
+      goto read_failed;
+
+    /* only evaluate samples for left channel */
+    for (i = 0; i < SAMPLES_PER_SECTOR; i += 2) {
+      gint16 pcm;
+
+      /* Native endianness first */
+      pcm = pcm_data[i];
+      ne_sumd0 += abs (pcm);
+      ne_sumd1 += abs (pcm - last_pcm_ne);
+      last_pcm_ne = pcm;
+
+      /* other endianness next */
+      pcm = GUINT16_SWAP_LE_BE (pcm);
+      oe_sumd0 += abs (pcm);
+      oe_sumd1 += abs (pcm - last_pcm_oe);
+      last_pcm_oe = pcm;
+    }
+
+  }
+
+  ne_factor = (ne_sumd1 / ne_sumd0);
+  oe_factor = (oe_sumd1 / oe_sumd0);
+  diff = ne_factor - oe_factor;
+
+  GST_DEBUG_OBJECT (src, "Native: %.2f, Other: %.2f, diff: %.2f",
+      ne_factor, oe_factor, diff);
+
+  if (diff > 0.5) {
+    GST_INFO_OBJECT (src, "Drive produces samples in other endianness");
+    src->swap_le_be = TRUE;
+    return TRUE;
+  } else if (diff < -0.5) {
+    GST_INFO_OBJECT (src, "Drive produces samples in host endianness");
+    src->swap_le_be = FALSE;
+    return TRUE;
+  } else {
+    GST_INFO_OBJECT (src, "Inconclusive, assuming host endianness");
+    src->swap_le_be = FALSE;
+    return FALSE;
+  }
+
+/* ERRORS */
+read_failed:
+  {
+    GST_WARNING_OBJECT (src, "could not read sector %d", sector);
+    src->swap_le_be = FALSE;
+    return FALSE;
+  }
+}
+
+static void
+gst_cdio_cdda_src_detect_drive_endianness (GstCdioCddaSrc * src, gint first,
+    gint last)
+{
+  gint from, to;
+
+  GST_INFO ("Detecting drive endianness");
+
+  /* try middle of disc first */
+  from = (first + last) / 2;
+  to = MIN (from + 10, last);
+  if (gst_cdio_cdda_src_do_detect_drive_endianness (src, from, to))
+    return;
+
+  /* if that was inconclusive, try other places */
+  from = (first + last) / 4;
+  to = MIN (from + 10, last);
+  if (gst_cdio_cdda_src_do_detect_drive_endianness (src, from, to))
+    return;
+
+  from = (first + last) * 3 / 4;
+  to = MIN (from + 10, last);
+  if (gst_cdio_cdda_src_do_detect_drive_endianness (src, from, to))
+    return;
+
+  /* if that's still inconclusive, we give up and assume host endianness */
+  return;
+}
+
 static gboolean
 notcdio_track_is_audio_track (const CdIo * p_cdio, track_t i_track)
 {
@@ -206,6 +316,7 @@ gst_cdio_cdda_src_open (GstAudioCdSrc * audiocdsrc, const gchar * device)
   GstCdioCddaSrc *src;
   discmode_t discmode;
   gint first_track, num_tracks, i;
+  gint first_audio_sector = 0, last_audio_sector = 0;
 #if LIBCDIO_VERSION_NUM > 83
   cdtext_t *cdtext;
 #endif
@@ -263,6 +374,11 @@ gst_cdio_cdda_src_open (GstAudioCdSrc * audiocdsrc, const gchar * device)
      * the right thing here (for cddb id calculations etc. as well) */
     track.start = cdio_get_track_lsn (src->cdio, i + first_track);
     track.end = track.start + len_sectors - 1;  /* -1? */
+
+    if (track.is_audio) {
+      first_audio_sector = MIN (first_audio_sector, track.start);
+      last_audio_sector = MAX (last_audio_sector, track.end);
+    }
 #if LIBCDIO_VERSION_NUM > 83
     if (NULL != cdtext)
       track.tags = gst_cdio_get_cdtext (GST_OBJECT (src), cdtext,
@@ -274,6 +390,13 @@ gst_cdio_cdda_src_open (GstAudioCdSrc * audiocdsrc, const gchar * device)
 
     gst_audio_cd_src_add_track (GST_AUDIO_CD_SRC (src), &track);
   }
+
+  /* Try to detect if we need to byte-order swap the samples coming from the
+   * drive, which might be the case if the CD drive operates in a different
+   * endianness than the host CPU's endianness (happens on e.g. Powerbook G4) */
+  gst_cdio_cdda_src_detect_drive_endianness (src, first_audio_sector,
+      last_audio_sector);
+
   return TRUE;
 
   /* ERRORS */

ext/cdio/gstcdiocddasrc.h

@@ -38,6 +38,8 @@ struct _GstCdioCddaSrc
 
   gint           read_speed;    /* ATOMIC */
 
+  gboolean       swap_le_be;    /* Drive produces samples in other endianness */
+
   CdIo          *cdio;          /* NULL if not open */
 };