LCOV - code coverage report
Current view: directory - media/libjpeg - jidctint.c (source / functions) Found Hit Coverage
Test: app.info Lines: 130 0 0.0 %
Date: 2012-06-02 Functions: 1 0 0.0 %

       1                 : /*
       2                 :  * jidctint.c
       3                 :  *
       4                 :  * Copyright (C) 1991-1998, Thomas G. Lane.
       5                 :  * This file is part of the Independent JPEG Group's software.
       6                 :  * For conditions of distribution and use, see the accompanying README file.
       7                 :  *
       8                 :  * This file contains a slow-but-accurate integer implementation of the
       9                 :  * inverse DCT (Discrete Cosine Transform).  In the IJG code, this routine
      10                 :  * must also perform dequantization of the input coefficients.
      11                 :  *
      12                 :  * A 2-D IDCT can be done by 1-D IDCT on each column followed by 1-D IDCT
      13                 :  * on each row (or vice versa, but it's more convenient to emit a row at
      14                 :  * a time).  Direct algorithms are also available, but they are much more
      15                 :  * complex and seem not to be any faster when reduced to code.
      16                 :  *
      17                 :  * This implementation is based on an algorithm described in
      18                 :  *   C. Loeffler, A. Ligtenberg and G. Moschytz, "Practical Fast 1-D DCT
      19                 :  *   Algorithms with 11 Multiplications", Proc. Int'l. Conf. on Acoustics,
      20                 :  *   Speech, and Signal Processing 1989 (ICASSP '89), pp. 988-991.
      21                 :  * The primary algorithm described there uses 11 multiplies and 29 adds.
      22                 :  * We use their alternate method with 12 multiplies and 32 adds.
      23                 :  * The advantage of this method is that no data path contains more than one
      24                 :  * multiplication; this allows a very simple and accurate implementation in
      25                 :  * scaled fixed-point arithmetic, with a minimal number of shifts.
      26                 :  */
      27                 : 
      28                 : #define JPEG_INTERNALS
      29                 : #include "jinclude.h"
      30                 : #include "jpeglib.h"
      31                 : #include "jdct.h"             /* Private declarations for DCT subsystem */
      32                 : 
      33                 : #ifdef DCT_ISLOW_SUPPORTED
      34                 : 
      35                 : 
      36                 : /*
      37                 :  * This module is specialized to the case DCTSIZE = 8.
      38                 :  */
      39                 : 
      40                 : #if DCTSIZE != 8
      41                 :   Sorry, this code only copes with 8x8 DCTs. /* deliberate syntax err */
      42                 : #endif
      43                 : 
      44                 : 
      45                 : /*
      46                 :  * The poop on this scaling stuff is as follows:
      47                 :  *
      48                 :  * Each 1-D IDCT step produces outputs which are a factor of sqrt(N)
      49                 :  * larger than the true IDCT outputs.  The final outputs are therefore
      50                 :  * a factor of N larger than desired; since N=8 this can be cured by
      51                 :  * a simple right shift at the end of the algorithm.  The advantage of
      52                 :  * this arrangement is that we save two multiplications per 1-D IDCT,
      53                 :  * because the y0 and y4 inputs need not be divided by sqrt(N).
      54                 :  *
      55                 :  * We have to do addition and subtraction of the integer inputs, which
      56                 :  * is no problem, and multiplication by fractional constants, which is
      57                 :  * a problem to do in integer arithmetic.  We multiply all the constants
      58                 :  * by CONST_SCALE and convert them to integer constants (thus retaining
      59                 :  * CONST_BITS bits of precision in the constants).  After doing a
      60                 :  * multiplication we have to divide the product by CONST_SCALE, with proper
      61                 :  * rounding, to produce the correct output.  This division can be done
      62                 :  * cheaply as a right shift of CONST_BITS bits.  We postpone shifting
      63                 :  * as long as possible so that partial sums can be added together with
      64                 :  * full fractional precision.
      65                 :  *
      66                 :  * The outputs of the first pass are scaled up by PASS1_BITS bits so that
      67                 :  * they are represented to better-than-integral precision.  These outputs
      68                 :  * require BITS_IN_JSAMPLE + PASS1_BITS + 3 bits; this fits in a 16-bit word
      69                 :  * with the recommended scaling.  (To scale up 12-bit sample data further, an
      70                 :  * intermediate INT32 array would be needed.)
      71                 :  *
      72                 :  * To avoid overflow of the 32-bit intermediate results in pass 2, we must
      73                 :  * have BITS_IN_JSAMPLE + CONST_BITS + PASS1_BITS <= 26.  Error analysis
      74                 :  * shows that the values given below are the most effective.
      75                 :  */
      76                 : 
      77                 : #if BITS_IN_JSAMPLE == 8
      78                 : #define CONST_BITS  13
      79                 : #define PASS1_BITS  2
      80                 : #else
      81                 : #define CONST_BITS  13
      82                 : #define PASS1_BITS  1           /* lose a little precision to avoid overflow */
      83                 : #endif
      84                 : 
      85                 : /* Some C compilers fail to reduce "FIX(constant)" at compile time, thus
      86                 :  * causing a lot of useless floating-point operations at run time.
      87                 :  * To get around this we use the following pre-calculated constants.
      88                 :  * If you change CONST_BITS you may want to add appropriate values.
      89                 :  * (With a reasonable C compiler, you can just rely on the FIX() macro...)
      90                 :  */
      91                 : 
      92                 : #if CONST_BITS == 13
      93                 : #define FIX_0_298631336  ((INT32)  2446)        /* FIX(0.298631336) */
      94                 : #define FIX_0_390180644  ((INT32)  3196)        /* FIX(0.390180644) */
      95                 : #define FIX_0_541196100  ((INT32)  4433)        /* FIX(0.541196100) */
      96                 : #define FIX_0_765366865  ((INT32)  6270)        /* FIX(0.765366865) */
      97                 : #define FIX_0_899976223  ((INT32)  7373)        /* FIX(0.899976223) */
      98                 : #define FIX_1_175875602  ((INT32)  9633)        /* FIX(1.175875602) */
      99                 : #define FIX_1_501321110  ((INT32)  12299)       /* FIX(1.501321110) */
     100                 : #define FIX_1_847759065  ((INT32)  15137)       /* FIX(1.847759065) */
     101                 : #define FIX_1_961570560  ((INT32)  16069)       /* FIX(1.961570560) */
     102                 : #define FIX_2_053119869  ((INT32)  16819)       /* FIX(2.053119869) */
     103                 : #define FIX_2_562915447  ((INT32)  20995)       /* FIX(2.562915447) */
     104                 : #define FIX_3_072711026  ((INT32)  25172)       /* FIX(3.072711026) */
     105                 : #else
     106                 : #define FIX_0_298631336  FIX(0.298631336)
     107                 : #define FIX_0_390180644  FIX(0.390180644)
     108                 : #define FIX_0_541196100  FIX(0.541196100)
     109                 : #define FIX_0_765366865  FIX(0.765366865)
     110                 : #define FIX_0_899976223  FIX(0.899976223)
     111                 : #define FIX_1_175875602  FIX(1.175875602)
     112                 : #define FIX_1_501321110  FIX(1.501321110)
     113                 : #define FIX_1_847759065  FIX(1.847759065)
     114                 : #define FIX_1_961570560  FIX(1.961570560)
     115                 : #define FIX_2_053119869  FIX(2.053119869)
     116                 : #define FIX_2_562915447  FIX(2.562915447)
     117                 : #define FIX_3_072711026  FIX(3.072711026)
     118                 : #endif
     119                 : 
     120                 : 
     121                 : /* Multiply an INT32 variable by an INT32 constant to yield an INT32 result.
     122                 :  * For 8-bit samples with the recommended scaling, all the variable
     123                 :  * and constant values involved are no more than 16 bits wide, so a
     124                 :  * 16x16->32 bit multiply can be used instead of a full 32x32 multiply.
     125                 :  * For 12-bit samples, a full 32-bit multiplication will be needed.
     126                 :  */
     127                 : 
     128                 : #if BITS_IN_JSAMPLE == 8
     129                 : #define MULTIPLY(var,const)  MULTIPLY16C16(var,const)
     130                 : #else
     131                 : #define MULTIPLY(var,const)  ((var) * (const))
     132                 : #endif
     133                 : 
     134                 : 
     135                 : /* Dequantize a coefficient by multiplying it by the multiplier-table
     136                 :  * entry; produce an int result.  In this module, both inputs and result
     137                 :  * are 16 bits or less, so either int or short multiply will work.
     138                 :  */
     139                 : 
     140                 : #define DEQUANTIZE(coef,quantval)  (((ISLOW_MULT_TYPE) (coef)) * (quantval))
     141                 : 
     142                 : 
     143                 : /*
     144                 :  * Perform dequantization and inverse DCT on one block of coefficients.
     145                 :  */
     146                 : 
     147                 : GLOBAL(void)
     148               0 : jpeg_idct_islow (j_decompress_ptr cinfo, jpeg_component_info * compptr,
     149                 :                  JCOEFPTR coef_block,
     150                 :                  JSAMPARRAY output_buf, JDIMENSION output_col)
     151                 : {
     152                 :   INT32 tmp0, tmp1, tmp2, tmp3;
     153                 :   INT32 tmp10, tmp11, tmp12, tmp13;
     154                 :   INT32 z1, z2, z3, z4, z5;
     155                 :   JCOEFPTR inptr;
     156                 :   ISLOW_MULT_TYPE * quantptr;
     157                 :   int * wsptr;
     158                 :   JSAMPROW outptr;
     159               0 :   JSAMPLE *range_limit = IDCT_range_limit(cinfo);
     160                 :   int ctr;
     161                 :   int workspace[DCTSIZE2];      /* buffers data between passes */
     162                 :   SHIFT_TEMPS
     163                 : 
     164                 :   /* Pass 1: process columns from input, store into work array. */
     165                 :   /* Note results are scaled up by sqrt(8) compared to a true IDCT; */
     166                 :   /* furthermore, we scale the results by 2**PASS1_BITS. */
     167                 : 
     168               0 :   inptr = coef_block;
     169               0 :   quantptr = (ISLOW_MULT_TYPE *) compptr->dct_table;
     170               0 :   wsptr = workspace;
     171               0 :   for (ctr = DCTSIZE; ctr > 0; ctr--) {
     172                 :     /* Due to quantization, we will usually find that many of the input
     173                 :      * coefficients are zero, especially the AC terms.  We can exploit this
     174                 :      * by short-circuiting the IDCT calculation for any column in which all
     175                 :      * the AC terms are zero.  In that case each output is equal to the
     176                 :      * DC coefficient (with scale factor as needed).
     177                 :      * With typical images and quantization tables, half or more of the
     178                 :      * column DCT calculations can be simplified this way.
     179                 :      */
     180                 :     
     181               0 :     if (inptr[DCTSIZE*1] == 0 && inptr[DCTSIZE*2] == 0 &&
     182               0 :         inptr[DCTSIZE*3] == 0 && inptr[DCTSIZE*4] == 0 &&
     183               0 :         inptr[DCTSIZE*5] == 0 && inptr[DCTSIZE*6] == 0 &&
     184               0 :         inptr[DCTSIZE*7] == 0) {
     185                 :       /* AC terms all zero */
     186               0 :       int dcval = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]) << PASS1_BITS;
     187                 :       
     188               0 :       wsptr[DCTSIZE*0] = dcval;
     189               0 :       wsptr[DCTSIZE*1] = dcval;
     190               0 :       wsptr[DCTSIZE*2] = dcval;
     191               0 :       wsptr[DCTSIZE*3] = dcval;
     192               0 :       wsptr[DCTSIZE*4] = dcval;
     193               0 :       wsptr[DCTSIZE*5] = dcval;
     194               0 :       wsptr[DCTSIZE*6] = dcval;
     195               0 :       wsptr[DCTSIZE*7] = dcval;
     196                 :       
     197               0 :       inptr++;                  /* advance pointers to next column */
     198               0 :       quantptr++;
     199               0 :       wsptr++;
     200               0 :       continue;
     201                 :     }
     202                 :     
     203                 :     /* Even part: reverse the even part of the forward DCT. */
     204                 :     /* The rotator is sqrt(2)*c(-6). */
     205                 :     
     206               0 :     z2 = DEQUANTIZE(inptr[DCTSIZE*2], quantptr[DCTSIZE*2]);
     207               0 :     z3 = DEQUANTIZE(inptr[DCTSIZE*6], quantptr[DCTSIZE*6]);
     208                 :     
     209               0 :     z1 = MULTIPLY(z2 + z3, FIX_0_541196100);
     210               0 :     tmp2 = z1 + MULTIPLY(z3, - FIX_1_847759065);
     211               0 :     tmp3 = z1 + MULTIPLY(z2, FIX_0_765366865);
     212                 :     
     213               0 :     z2 = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]);
     214               0 :     z3 = DEQUANTIZE(inptr[DCTSIZE*4], quantptr[DCTSIZE*4]);
     215                 : 
     216               0 :     tmp0 = (z2 + z3) << CONST_BITS;
     217               0 :     tmp1 = (z2 - z3) << CONST_BITS;
     218                 :     
     219               0 :     tmp10 = tmp0 + tmp3;
     220               0 :     tmp13 = tmp0 - tmp3;
     221               0 :     tmp11 = tmp1 + tmp2;
     222               0 :     tmp12 = tmp1 - tmp2;
     223                 :     
     224                 :     /* Odd part per figure 8; the matrix is unitary and hence its
     225                 :      * transpose is its inverse.  i0..i3 are y7,y5,y3,y1 respectively.
     226                 :      */
     227                 :     
     228               0 :     tmp0 = DEQUANTIZE(inptr[DCTSIZE*7], quantptr[DCTSIZE*7]);
     229               0 :     tmp1 = DEQUANTIZE(inptr[DCTSIZE*5], quantptr[DCTSIZE*5]);
     230               0 :     tmp2 = DEQUANTIZE(inptr[DCTSIZE*3], quantptr[DCTSIZE*3]);
     231               0 :     tmp3 = DEQUANTIZE(inptr[DCTSIZE*1], quantptr[DCTSIZE*1]);
     232                 :     
     233               0 :     z1 = tmp0 + tmp3;
     234               0 :     z2 = tmp1 + tmp2;
     235               0 :     z3 = tmp0 + tmp2;
     236               0 :     z4 = tmp1 + tmp3;
     237               0 :     z5 = MULTIPLY(z3 + z4, FIX_1_175875602); /* sqrt(2) * c3 */
     238                 :     
     239               0 :     tmp0 = MULTIPLY(tmp0, FIX_0_298631336); /* sqrt(2) * (-c1+c3+c5-c7) */
     240               0 :     tmp1 = MULTIPLY(tmp1, FIX_2_053119869); /* sqrt(2) * ( c1+c3-c5+c7) */
     241               0 :     tmp2 = MULTIPLY(tmp2, FIX_3_072711026); /* sqrt(2) * ( c1+c3+c5-c7) */
     242               0 :     tmp3 = MULTIPLY(tmp3, FIX_1_501321110); /* sqrt(2) * ( c1+c3-c5-c7) */
     243               0 :     z1 = MULTIPLY(z1, - FIX_0_899976223); /* sqrt(2) * (c7-c3) */
     244               0 :     z2 = MULTIPLY(z2, - FIX_2_562915447); /* sqrt(2) * (-c1-c3) */
     245               0 :     z3 = MULTIPLY(z3, - FIX_1_961570560); /* sqrt(2) * (-c3-c5) */
     246               0 :     z4 = MULTIPLY(z4, - FIX_0_390180644); /* sqrt(2) * (c5-c3) */
     247                 :     
     248               0 :     z3 += z5;
     249               0 :     z4 += z5;
     250                 :     
     251               0 :     tmp0 += z1 + z3;
     252               0 :     tmp1 += z2 + z4;
     253               0 :     tmp2 += z2 + z3;
     254               0 :     tmp3 += z1 + z4;
     255                 :     
     256                 :     /* Final output stage: inputs are tmp10..tmp13, tmp0..tmp3 */
     257                 :     
     258               0 :     wsptr[DCTSIZE*0] = (int) DESCALE(tmp10 + tmp3, CONST_BITS-PASS1_BITS);
     259               0 :     wsptr[DCTSIZE*7] = (int) DESCALE(tmp10 - tmp3, CONST_BITS-PASS1_BITS);
     260               0 :     wsptr[DCTSIZE*1] = (int) DESCALE(tmp11 + tmp2, CONST_BITS-PASS1_BITS);
     261               0 :     wsptr[DCTSIZE*6] = (int) DESCALE(tmp11 - tmp2, CONST_BITS-PASS1_BITS);
     262               0 :     wsptr[DCTSIZE*2] = (int) DESCALE(tmp12 + tmp1, CONST_BITS-PASS1_BITS);
     263               0 :     wsptr[DCTSIZE*5] = (int) DESCALE(tmp12 - tmp1, CONST_BITS-PASS1_BITS);
     264               0 :     wsptr[DCTSIZE*3] = (int) DESCALE(tmp13 + tmp0, CONST_BITS-PASS1_BITS);
     265               0 :     wsptr[DCTSIZE*4] = (int) DESCALE(tmp13 - tmp0, CONST_BITS-PASS1_BITS);
     266                 :     
     267               0 :     inptr++;                    /* advance pointers to next column */
     268               0 :     quantptr++;
     269               0 :     wsptr++;
     270                 :   }
     271                 :   
     272                 :   /* Pass 2: process rows from work array, store into output array. */
     273                 :   /* Note that we must descale the results by a factor of 8 == 2**3, */
     274                 :   /* and also undo the PASS1_BITS scaling. */
     275                 : 
     276               0 :   wsptr = workspace;
     277               0 :   for (ctr = 0; ctr < DCTSIZE; ctr++) {
     278               0 :     outptr = output_buf[ctr] + output_col;
     279                 :     /* Rows of zeroes can be exploited in the same way as we did with columns.
     280                 :      * However, the column calculation has created many nonzero AC terms, so
     281                 :      * the simplification applies less often (typically 5% to 10% of the time).
     282                 :      * On machines with very fast multiplication, it's possible that the
     283                 :      * test takes more time than it's worth.  In that case this section
     284                 :      * may be commented out.
     285                 :      */
     286                 :     
     287                 : #ifndef NO_ZERO_ROW_TEST
     288               0 :     if (wsptr[1] == 0 && wsptr[2] == 0 && wsptr[3] == 0 && wsptr[4] == 0 &&
     289               0 :         wsptr[5] == 0 && wsptr[6] == 0 && wsptr[7] == 0) {
     290                 :       /* AC terms all zero */
     291               0 :       JSAMPLE dcval = range_limit[(int) DESCALE((INT32) wsptr[0], PASS1_BITS+3)
     292                 :                                   & RANGE_MASK];
     293                 :       
     294               0 :       outptr[0] = dcval;
     295               0 :       outptr[1] = dcval;
     296               0 :       outptr[2] = dcval;
     297               0 :       outptr[3] = dcval;
     298               0 :       outptr[4] = dcval;
     299               0 :       outptr[5] = dcval;
     300               0 :       outptr[6] = dcval;
     301               0 :       outptr[7] = dcval;
     302                 : 
     303               0 :       wsptr += DCTSIZE;         /* advance pointer to next row */
     304               0 :       continue;
     305                 :     }
     306                 : #endif
     307                 :     
     308                 :     /* Even part: reverse the even part of the forward DCT. */
     309                 :     /* The rotator is sqrt(2)*c(-6). */
     310                 :     
     311               0 :     z2 = (INT32) wsptr[2];
     312               0 :     z3 = (INT32) wsptr[6];
     313                 :     
     314               0 :     z1 = MULTIPLY(z2 + z3, FIX_0_541196100);
     315               0 :     tmp2 = z1 + MULTIPLY(z3, - FIX_1_847759065);
     316               0 :     tmp3 = z1 + MULTIPLY(z2, FIX_0_765366865);
     317                 :     
     318               0 :     tmp0 = ((INT32) wsptr[0] + (INT32) wsptr[4]) << CONST_BITS;
     319               0 :     tmp1 = ((INT32) wsptr[0] - (INT32) wsptr[4]) << CONST_BITS;
     320                 :     
     321               0 :     tmp10 = tmp0 + tmp3;
     322               0 :     tmp13 = tmp0 - tmp3;
     323               0 :     tmp11 = tmp1 + tmp2;
     324               0 :     tmp12 = tmp1 - tmp2;
     325                 :     
     326                 :     /* Odd part per figure 8; the matrix is unitary and hence its
     327                 :      * transpose is its inverse.  i0..i3 are y7,y5,y3,y1 respectively.
     328                 :      */
     329                 :     
     330               0 :     tmp0 = (INT32) wsptr[7];
     331               0 :     tmp1 = (INT32) wsptr[5];
     332               0 :     tmp2 = (INT32) wsptr[3];
     333               0 :     tmp3 = (INT32) wsptr[1];
     334                 :     
     335               0 :     z1 = tmp0 + tmp3;
     336               0 :     z2 = tmp1 + tmp2;
     337               0 :     z3 = tmp0 + tmp2;
     338               0 :     z4 = tmp1 + tmp3;
     339               0 :     z5 = MULTIPLY(z3 + z4, FIX_1_175875602); /* sqrt(2) * c3 */
     340                 :     
     341               0 :     tmp0 = MULTIPLY(tmp0, FIX_0_298631336); /* sqrt(2) * (-c1+c3+c5-c7) */
     342               0 :     tmp1 = MULTIPLY(tmp1, FIX_2_053119869); /* sqrt(2) * ( c1+c3-c5+c7) */
     343               0 :     tmp2 = MULTIPLY(tmp2, FIX_3_072711026); /* sqrt(2) * ( c1+c3+c5-c7) */
     344               0 :     tmp3 = MULTIPLY(tmp3, FIX_1_501321110); /* sqrt(2) * ( c1+c3-c5-c7) */
     345               0 :     z1 = MULTIPLY(z1, - FIX_0_899976223); /* sqrt(2) * (c7-c3) */
     346               0 :     z2 = MULTIPLY(z2, - FIX_2_562915447); /* sqrt(2) * (-c1-c3) */
     347               0 :     z3 = MULTIPLY(z3, - FIX_1_961570560); /* sqrt(2) * (-c3-c5) */
     348               0 :     z4 = MULTIPLY(z4, - FIX_0_390180644); /* sqrt(2) * (c5-c3) */
     349                 :     
     350               0 :     z3 += z5;
     351               0 :     z4 += z5;
     352                 :     
     353               0 :     tmp0 += z1 + z3;
     354               0 :     tmp1 += z2 + z4;
     355               0 :     tmp2 += z2 + z3;
     356               0 :     tmp3 += z1 + z4;
     357                 :     
     358                 :     /* Final output stage: inputs are tmp10..tmp13, tmp0..tmp3 */
     359                 :     
     360               0 :     outptr[0] = range_limit[(int) DESCALE(tmp10 + tmp3,
     361                 :                                           CONST_BITS+PASS1_BITS+3)
     362                 :                             & RANGE_MASK];
     363               0 :     outptr[7] = range_limit[(int) DESCALE(tmp10 - tmp3,
     364                 :                                           CONST_BITS+PASS1_BITS+3)
     365                 :                             & RANGE_MASK];
     366               0 :     outptr[1] = range_limit[(int) DESCALE(tmp11 + tmp2,
     367                 :                                           CONST_BITS+PASS1_BITS+3)
     368                 :                             & RANGE_MASK];
     369               0 :     outptr[6] = range_limit[(int) DESCALE(tmp11 - tmp2,
     370                 :                                           CONST_BITS+PASS1_BITS+3)
     371                 :                             & RANGE_MASK];
     372               0 :     outptr[2] = range_limit[(int) DESCALE(tmp12 + tmp1,
     373                 :                                           CONST_BITS+PASS1_BITS+3)
     374                 :                             & RANGE_MASK];
     375               0 :     outptr[5] = range_limit[(int) DESCALE(tmp12 - tmp1,
     376                 :                                           CONST_BITS+PASS1_BITS+3)
     377                 :                             & RANGE_MASK];
     378               0 :     outptr[3] = range_limit[(int) DESCALE(tmp13 + tmp0,
     379                 :                                           CONST_BITS+PASS1_BITS+3)
     380                 :                             & RANGE_MASK];
     381               0 :     outptr[4] = range_limit[(int) DESCALE(tmp13 - tmp0,
     382                 :                                           CONST_BITS+PASS1_BITS+3)
     383                 :                             & RANGE_MASK];
     384                 :     
     385               0 :     wsptr += DCTSIZE;           /* advance pointer to next row */
     386                 :   }
     387               0 : }
     388                 : 
     389                 : #endif /* DCT_ISLOW_SUPPORTED */

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