00171 {
00172   DCTELEM tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7;
00173   DCTELEM tmp10, tmp11, tmp12, tmp13;
00174   DCTELEM z5, z10, z11, z12, z13;
00175   JCOEFPTR inptr;
00176   IFAST_MULT_TYPE * quantptr;
00177   int * wsptr;
00178   JSAMPROW outptr;
00179   JSAMPLE *range_limit = IDCT_range_limit(cinfo);
00180   int ctr;
00181   int workspace[DCTSIZE2];      /* buffers data between passes */
00182   SHIFT_TEMPS                   /* for DESCALE */
00183   ISHIFT_TEMPS                  /* for IDESCALE */
00184 
00185   /* Pass 1: process columns from input, store into work array. */
00186 
00187   inptr = coef_block;
00188   quantptr = (IFAST_MULT_TYPE *) compptr->dct_table;
00189   wsptr = workspace;
00190   for (ctr = DCTSIZE; ctr > 0; ctr--) {
00191     /* Due to quantization, we will usually find that many of the input
00192      * coefficients are zero, especially the AC terms.  We can exploit this
00193      * by short-circuiting the IDCT calculation for any column in which all
00194      * the AC terms are zero.  In that case each output is equal to the
00195      * DC coefficient (with scale factor as needed).
00196      * With typical images and quantization tables, half or more of the
00197      * column DCT calculations can be simplified this way.
00198      */
00199     
00200     if (inptr[DCTSIZE*1] == 0 && inptr[DCTSIZE*2] == 0 &&
00201         inptr[DCTSIZE*3] == 0 && inptr[DCTSIZE*4] == 0 &&
00202         inptr[DCTSIZE*5] == 0 && inptr[DCTSIZE*6] == 0 &&
00203         inptr[DCTSIZE*7] == 0) {
00204       /* AC terms all zero */
00205       int dcval = (int) DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]);
00206 
00207       wsptr[DCTSIZE*0] = dcval;
00208       wsptr[DCTSIZE*1] = dcval;
00209       wsptr[DCTSIZE*2] = dcval;
00210       wsptr[DCTSIZE*3] = dcval;
00211       wsptr[DCTSIZE*4] = dcval;
00212       wsptr[DCTSIZE*5] = dcval;
00213       wsptr[DCTSIZE*6] = dcval;
00214       wsptr[DCTSIZE*7] = dcval;
00215       
00216       inptr++;                  /* advance pointers to next column */
00217       quantptr++;
00218       wsptr++;
00219       continue;
00220     }
00221     
00222     /* Even part */
00223 
00224     tmp0 = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]);
00225     tmp1 = DEQUANTIZE(inptr[DCTSIZE*2], quantptr[DCTSIZE*2]);
00226     tmp2 = DEQUANTIZE(inptr[DCTSIZE*4], quantptr[DCTSIZE*4]);
00227     tmp3 = DEQUANTIZE(inptr[DCTSIZE*6], quantptr[DCTSIZE*6]);
00228 
00229     tmp10 = tmp0 + tmp2;        /* phase 3 */
00230     tmp11 = tmp0 - tmp2;
00231 
00232     tmp13 = tmp1 + tmp3;        /* phases 5-3 */
00233     tmp12 = MULTIPLY(tmp1 - tmp3, FIX_1_414213562) - tmp13; /* 2*c4 */
00234 
00235     tmp0 = tmp10 + tmp13;       /* phase 2 */
00236     tmp3 = tmp10 - tmp13;
00237     tmp1 = tmp11 + tmp12;
00238     tmp2 = tmp11 - tmp12;
00239     
00240     /* Odd part */
00241 
00242     tmp4 = DEQUANTIZE(inptr[DCTSIZE*1], quantptr[DCTSIZE*1]);
00243     tmp5 = DEQUANTIZE(inptr[DCTSIZE*3], quantptr[DCTSIZE*3]);
00244     tmp6 = DEQUANTIZE(inptr[DCTSIZE*5], quantptr[DCTSIZE*5]);
00245     tmp7 = DEQUANTIZE(inptr[DCTSIZE*7], quantptr[DCTSIZE*7]);
00246 
00247     z13 = tmp6 + tmp5;          /* phase 6 */
00248     z10 = tmp6 - tmp5;
00249     z11 = tmp4 + tmp7;
00250     z12 = tmp4 - tmp7;
00251 
00252     tmp7 = z11 + z13;           /* phase 5 */
00253     tmp11 = MULTIPLY(z11 - z13, FIX_1_414213562); /* 2*c4 */
00254 
00255     z5 = MULTIPLY(z10 + z12, FIX_1_847759065); /* 2*c2 */
00256     tmp10 = MULTIPLY(z12, FIX_1_082392200) - z5; /* 2*(c2-c6) */
00257     tmp12 = MULTIPLY(z10, - FIX_2_613125930) + z5; /* -2*(c2+c6) */
00258 
00259     tmp6 = tmp12 - tmp7;        /* phase 2 */
00260     tmp5 = tmp11 - tmp6;
00261     tmp4 = tmp10 + tmp5;
00262 
00263     wsptr[DCTSIZE*0] = (int) (tmp0 + tmp7);
00264     wsptr[DCTSIZE*7] = (int) (tmp0 - tmp7);
00265     wsptr[DCTSIZE*1] = (int) (tmp1 + tmp6);
00266     wsptr[DCTSIZE*6] = (int) (tmp1 - tmp6);
00267     wsptr[DCTSIZE*2] = (int) (tmp2 + tmp5);
00268     wsptr[DCTSIZE*5] = (int) (tmp2 - tmp5);
00269     wsptr[DCTSIZE*4] = (int) (tmp3 + tmp4);
00270     wsptr[DCTSIZE*3] = (int) (tmp3 - tmp4);
00271 
00272     inptr++;                    /* advance pointers to next column */
00273     quantptr++;
00274     wsptr++;
00275   }
00276   
00277   /* Pass 2: process rows from work array, store into output array. */
00278   /* Note that we must descale the results by a factor of 8 == 2**3, */
00279   /* and also undo the PASS1_BITS scaling. */
00280 
00281   wsptr = workspace;
00282   for (ctr = 0; ctr < DCTSIZE; ctr++) {
00283     outptr = output_buf[ctr] + output_col;
00284     /* Rows of zeroes can be exploited in the same way as we did with columns.
00285      * However, the column calculation has created many nonzero AC terms, so
00286      * the simplification applies less often (typically 5% to 10% of the time).
00287      * On machines with very fast multiplication, it's possible that the
00288      * test takes more time than it's worth.  In that case this section
00289      * may be commented out.
00290      */
00291     
00292 #ifndef NO_ZERO_ROW_TEST
00293     if (wsptr[1] == 0 && wsptr[2] == 0 && wsptr[3] == 0 && wsptr[4] == 0 &&
00294         wsptr[5] == 0 && wsptr[6] == 0 && wsptr[7] == 0) {
00295       /* AC terms all zero */
00296       JSAMPLE dcval = range_limit[IDESCALE(wsptr[0], PASS1_BITS+3)
00297                                   & RANGE_MASK];
00298       
00299       outptr[0] = dcval;
00300       outptr[1] = dcval;
00301       outptr[2] = dcval;
00302       outptr[3] = dcval;
00303       outptr[4] = dcval;
00304       outptr[5] = dcval;
00305       outptr[6] = dcval;
00306       outptr[7] = dcval;
00307 
00308       wsptr += DCTSIZE;         /* advance pointer to next row */
00309       continue;
00310     }
00311 #endif
00312     
00313     /* Even part */
00314 
00315     tmp10 = ((DCTELEM) wsptr[0] + (DCTELEM) wsptr[4]);
00316     tmp11 = ((DCTELEM) wsptr[0] - (DCTELEM) wsptr[4]);
00317 
00318     tmp13 = ((DCTELEM) wsptr[2] + (DCTELEM) wsptr[6]);
00319     tmp12 = MULTIPLY((DCTELEM) wsptr[2] - (DCTELEM) wsptr[6], FIX_1_414213562)
00320             - tmp13;
00321 
00322     tmp0 = tmp10 + tmp13;
00323     tmp3 = tmp10 - tmp13;
00324     tmp1 = tmp11 + tmp12;
00325     tmp2 = tmp11 - tmp12;
00326 
00327     /* Odd part */
00328 
00329     z13 = (DCTELEM) wsptr[5] + (DCTELEM) wsptr[3];
00330     z10 = (DCTELEM) wsptr[5] - (DCTELEM) wsptr[3];
00331     z11 = (DCTELEM) wsptr[1] + (DCTELEM) wsptr[7];
00332     z12 = (DCTELEM) wsptr[1] - (DCTELEM) wsptr[7];
00333 
00334     tmp7 = z11 + z13;           /* phase 5 */
00335     tmp11 = MULTIPLY(z11 - z13, FIX_1_414213562); /* 2*c4 */
00336 
00337     z5 = MULTIPLY(z10 + z12, FIX_1_847759065); /* 2*c2 */
00338     tmp10 = MULTIPLY(z12, FIX_1_082392200) - z5; /* 2*(c2-c6) */
00339     tmp12 = MULTIPLY(z10, - FIX_2_613125930) + z5; /* -2*(c2+c6) */
00340 
00341     tmp6 = tmp12 - tmp7;        /* phase 2 */
00342     tmp5 = tmp11 - tmp6;
00343     tmp4 = tmp10 + tmp5;
00344 
00345     /* Final output stage: scale down by a factor of 8 and range-limit */
00346 
00347     outptr[0] = range_limit[IDESCALE(tmp0 + tmp7, PASS1_BITS+3)
00348                             & RANGE_MASK];
00349     outptr[7] = range_limit[IDESCALE(tmp0 - tmp7, PASS1_BITS+3)
00350                             & RANGE_MASK];
00351     outptr[1] = range_limit[IDESCALE(tmp1 + tmp6, PASS1_BITS+3)
00352                             & RANGE_MASK];
00353     outptr[6] = range_limit[IDESCALE(tmp1 - tmp6, PASS1_BITS+3)
00354                             & RANGE_MASK];
00355     outptr[2] = range_limit[IDESCALE(tmp2 + tmp5, PASS1_BITS+3)
00356                             & RANGE_MASK];
00357     outptr[5] = range_limit[IDESCALE(tmp2 - tmp5, PASS1_BITS+3)
00358                             & RANGE_MASK];
00359     outptr[4] = range_limit[IDESCALE(tmp3 + tmp4, PASS1_BITS+3)
00360                             & RANGE_MASK];
00361     outptr[3] = range_limit[IDESCALE(tmp3 - tmp4, PASS1_BITS+3)
00362                             & RANGE_MASK];
00363 
00364     wsptr += DCTSIZE;           /* advance pointer to next row */
00365   }
00366 }