saturate MDCT output

2 files changed, 7 insertions, 4 deletions

diff --git a/celt/arch.h b/celt/arch.h
index 05e434b9..1615af39 100644
--- a/celt/arch.h
+++ b/celt/arch.h
@@ -101,6 +101,9 @@ typedef opus_val32 celt_ener;
 #define Q15ONE 32767
 
 #define SIG_SHIFT 12
+/* Safe saturation value for 32-bit signals. Should be less than
+   2^31*(1-0.85) to avoid blowing up on DC at deemphasis.*/
+#define SIG_SAT (300000000)
 
 #define NORM_SCALING 16384
 
diff --git a/celt/mdct.c b/celt/mdct.c
index 5c6dab5b..a8497c66 100644
--- a/celt/mdct.c
+++ b/celt/mdct.c
@@ -306,16 +306,16 @@ void clt_mdct_backward_c(const mdct_lookup *l, kiss_fft_scalar *in, kiss_fft_sca
          /* We swap real and imag because we're using an FFT instead of an IFFT. */
          re = yp1[1];
          im = yp1[0];
-         yp0[0] = yr;
-         yp1[1] = yi;
+         yp0[0] = SATURATE(yr, SIG_SAT);
+         yp1[1] = SATURATE(yi, SIG_SAT);
 
          t0 = t[(N4-i-1)];
          t1 = t[(N2-i-1)];
          /* We'd scale up by 2 here, but instead it's done when mixing the windows */
          yr = ADD32_ovflw(S_MUL(re,t0), S_MUL(im,t1));
          yi = SUB32_ovflw(S_MUL(re,t1), S_MUL(im,t0));
-         yp1[0] = yr;
-         yp0[1] = yi;
+         yp1[0] = SATURATE(yr, SIG_SAT);
+         yp0[1] = SATURATE(yi, SIG_SAT);
          yp0 += 2;
          yp1 -= 2;
       }