Fix UBSan errors (left shift of negative value)

webrtc/modules/audio_coding/codecs/ilbc/get_lsp_poly.c

Index: webrtc/modules/audio_coding/codecs/ilbc/get_lsp_poly.c
diff --git a/webrtc/modules/audio_coding/codecs/ilbc/get_lsp_poly.c b/webrtc/modules/audio_coding/codecs/ilbc/get_lsp_poly.c
index 62a686495b1c3e4572ce43d2e1bd9155e7773467..a8375afb609246ff78e0e92b43dbb3f5f8587782 100644
--- a/webrtc/modules/audio_coding/codecs/ilbc/get_lsp_poly.c
+++ b/webrtc/modules/audio_coding/codecs/ilbc/get_lsp_poly.c
@@ -65,15 +65,15 @@ void WebRtcIlbcfix_GetLspPoly(
     {
       /* Compute f[j] = f[j] + tmp*f[j-1] + f[j-2]; */
       high = (int16_t)(fPtr[-1] >> 16);
-      low = (int16_t)((fPtr[-1] - ((int32_t)high << 16)) >> 1);
+      low = (int16_t)((fPtr[-1] & 0xffff) >> 1);

[tlegrand, 2016/05/17 12:24:32]

This is so much nicer!

[kwiberg-webrtc, 2016/05/17 12:32:29]

I've found the "x_low = x - x_high << 16" pattern in other places too. It
appears someone was in the habit of writing it that way...

Luckily, the compiler is smart enough to generate the same code regardless, so
this is just a source code improvement.

 
-      tmpW32 = ((high * *lspPtr) << 2) + (((low * *lspPtr) >> 15) << 2);
+      tmpW32 = 4 * high * *lspPtr + 4 * ((low * *lspPtr) >> 15);
 
       (*fPtr) += fPtr[-2];
       (*fPtr) -= tmpW32;
       fPtr--;
     }
-    *fPtr -= *lspPtr << 10;
+    *fPtr -= *lspPtr * (1 << 10);
 
     fPtr+=i;
     lspPtr+=2;