mpegvideo_enc: factor out denominator and explicitly cast operands

CC: libav-stable@libav.org
Bug-Id: CID 608053

libavcodec/mpegvideo_enc.c

@@ -95,42 +95,40 @@ void ff_convert_matrix(MpegEncContext *s, int (*qmat)[64],
             fdsp->fdct == ff_jpeg_fdct_islow_10) {
             for (i = 0; i < 64; i++) {
                 const int j = s->idsp.idct_permutation[i];
+                int64_t den = (int64_t) qscale * quant_matrix[j];
                 /* 16 <= qscale * quant_matrix[i] <= 7905
                  * Assume x = ff_aanscales[i] * qscale * quant_matrix[i]
                  *             19952 <=              x  <= 249205026
                  * (1 << 36) / 19952 >= (1 << 36) / (x) >= (1 << 36) / 249205026
                  *           3444240 >= (1 << 36) / (x) >= 275 */
 
-                qmat[qscale][i] = (int)((UINT64_C(1) << QMAT_SHIFT) /
-                                        (qscale * quant_matrix[j]));
+                qmat[qscale][i] = (int)((UINT64_C(1) << QMAT_SHIFT) / den);
             }
         } else if (fdsp->fdct == ff_fdct_ifast) {
             for (i = 0; i < 64; i++) {
                 const int j = s->idsp.idct_permutation[i];
+                int64_t den = ff_aanscales[i] * (int64_t) qscale * quant_matrix[j];
                 /* 16 <= qscale * quant_matrix[i] <= 7905
                  * Assume x = ff_aanscales[i] * qscale * quant_matrix[i]
                  *             19952 <=              x  <= 249205026
                  * (1 << 36) / 19952 >= (1 << 36) / (x) >= (1 << 36) / 249205026
                  *           3444240 >= (1 << 36) / (x) >= 275 */
 
-                qmat[qscale][i] = (int)((UINT64_C(1) << (QMAT_SHIFT + 14)) /
-                                        (ff_aanscales[i] * qscale *
-                                         quant_matrix[j]));
+                qmat[qscale][i] = (int)((UINT64_C(1) << (QMAT_SHIFT + 14)) / den);
             }
         } else {
             for (i = 0; i < 64; i++) {
                 const int j = s->idsp.idct_permutation[i];
+                int64_t den = (int64_t) qscale * quant_matrix[j];
                 /* We can safely suppose that 16 <= quant_matrix[i] <= 255
                  * Assume x = qscale * quant_matrix[i]
                  * So             16 <=              x  <= 7905
                  * so (1 << 19) / 16 >= (1 << 19) / (x) >= (1 << 19) / 7905
                  * so          32768 >= (1 << 19) / (x) >= 67 */
-                qmat[qscale][i] = (int)((UINT64_C(1) << QMAT_SHIFT) /
-                                        (qscale * quant_matrix[j]));
+                qmat[qscale][i] = (int)((UINT64_C(1) << QMAT_SHIFT) / den);
                 //qmat  [qscale][i] = (1 << QMAT_SHIFT_MMX) /
                 //                    (qscale * quant_matrix[i]);
-                qmat16[qscale][0][i] = (1 << QMAT_SHIFT_MMX) /
-                                       (qscale * quant_matrix[j]);
+                qmat16[qscale][0][i] = (1 << QMAT_SHIFT_MMX) / den;
 
                 if (qmat16[qscale][0][i] == 0 ||
                     qmat16[qscale][0][i] == 128 * 256)