Implement lms_update()

(cherry picked from commit 17219c79360bc2bdaf3e7f47178af42fade140a8)
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/wmalosslessdec.c

@@ -774,6 +774,55 @@ static int lms_predict(WmallDecodeCtx *s, int ich, int ilms)
     return pred;
 }
 
+static void lms_update(WmallDecodeCtx *s, int ich, int ilms, int32_t input, int32_t pred)
+{
+    int icoef;
+    int recent = s->cdlms[ich][ilms].recent;
+    int range = 1 << (s->bits_per_sample - 1);
+    int bps = s->bits_per_sample > 16 ? 4 : 2; // bytes per sample
+
+    if (input > pred) {
+        for (icoef = 0; icoef < s->cdlms[ich][ilms].order; icoef++)
+            s->cdlms[ich][ilms].coefs[icoef] +=
+                s->cdlms[ich][ilms].lms_updates[icoef + recent];
+    } else {
+        for (icoef = 0; icoef < s->cdlms[ich][ilms].order; icoef++)
+            s->cdlms[ich][ilms].coefs[icoef] -=
+                s->cdlms[ich][ilms].lms_updates[icoef];     // XXX: [icoef + recent] ?
+    }
+    s->cdlms[ich][ilms].recent--;
+    s->cdlms[ich][ilms].lms_prevvalues[recent] = av_clip(input, -range, range - 1);
+
+    if (input > pred)
+        s->cdlms[ich][ilms].lms_updates[recent] = s->update_speed[ich];
+    else if (input < pred)
+        s->cdlms[ich][ilms].lms_updates[recent] = -s->update_speed[ich];
+
+    /* XXX: spec says:
+    cdlms[iCh][ilms].updates[iRecent + cdlms[iCh][ilms].order >> 4] >>= 2;
+    lms_updates[iCh][ilms][iRecent + cdlms[iCh][ilms].order >> 3] >>= 1;
+
+        Questions is - are cdlms[iCh][ilms].updates[] and lms_updates[][][] two
+        seperate buffers? Here I've assumed that the two are same which makes
+        more sense to me.
+    */
+    s->cdlms[ich][ilms].lms_updates[recent + s->cdlms[ich][ilms].order >> 4] >>= 2;
+    s->cdlms[ich][ilms].lms_updates[recent + s->cdlms[ich][ilms].order >> 3] >>= 1;
+    /* XXX: recent + (s->cdlms[ich][ilms].order >> 4) ? */
+
+    if (s->cdlms[ich][ilms].recent == 0) {
+        /* XXX: This memcpy()s will probably fail if a fixed 32-bit buffer is used.
+                follow kshishkov's suggestion of using a union. */
+        memcpy(s->cdlms[ich][ilms].lms_prevvalues + s->cdlms[ich][ilms].order,
+               s->cdlms[ich][ilms].lms_prevvalues,
+               bps * s->cdlms[ich][ilms].order);
+        memcpy(s->cdlms[ich][ilms].lms_updates + s->cdlms[ich][ilms].order,
+               s->cdlms[ich][ilms].lms_updates,
+               bps * s->cdlms[ich][ilms].order);
+        s->cdlms[ich][ilms].recent = s->cdlms[ich][ilms].order;
+    }
+}
+
 /**
  *@brief Decode a single subframe (block).
  *@param s codec context