return ret;
}
+static inline DCTELEM dequant(DCTELEM in, uint32_t quant, int dc)
+{
+ /* Note: multiplication is unsigned but we want signed shift
+ * otherwise clipping breaks.
+ * TODO: The official decoder does not use clipping at all
+ * but instead uses the full 32-bit result.
+ * However clipping at least gets rid of the case that a
+ * half-black half-white intra block gets black and white swapped
+ * and should cause at most minor differences (except for DC). */
+ int32_t res = in * quant;
+ res >>= 11;
+ if (!dc)
+ res = av_clip_int16(res);
+ return res;
+}
+
/**
* Read 8x8 block of DCT coefficients.
*
quant = quant_matrices[quant_idx];
- block[0] = (block[0] * quant[0]) >> 11;
+ block[0] = dequant(block[0], quant[0], 1);
for (i = 0; i < coef_count; i++) {
int idx = coef_idx[i];
- block[scan[idx]] = (block[scan[idx]] * quant[idx]) >> 11;
+ block[scan[idx]] = dequant(block[scan[idx]], quant[idx], 0);
}
return 0;