| 1 | /*
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| 2 | * jidctred.c
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| 3 | *
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| 4 | * Copyright (C) 1994-1998, Thomas G. Lane.
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| 5 | * This file is part of the Independent JPEG Group's software.
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| 6 | * For conditions of distribution and use, see the accompanying README file.
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| 7 | *
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| 8 | * This file contains inverse-DCT routines that produce reduced-size output:
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| 9 | * either 4x4, 2x2, or 1x1 pixels from an 8x8 DCT block.
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| 10 | *
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| 11 | * The implementation is based on the Loeffler, Ligtenberg and Moschytz (LL&M)
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| 12 | * algorithm used in jidctint.c. We simply replace each 8-to-8 1-D IDCT step
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| 13 | * with an 8-to-4 step that produces the four averages of two adjacent outputs
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| 14 | * (or an 8-to-2 step producing two averages of four outputs, for 2x2 output).
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| 15 | * These steps were derived by computing the corresponding values at the end
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| 16 | * of the normal LL&M code, then simplifying as much as possible.
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| 17 | *
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| 18 | * 1x1 is trivial: just take the DC coefficient divided by 8.
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| 19 | *
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| 20 | * See jidctint.c for additional comments.
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| 21 | */
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| 22 |
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| 23 | #define JPEG_INTERNALS
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| 24 | #include "jinclude.h"
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| 25 | #include "jpeglib.h"
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| 26 | #include "jdct.h" /* Private declarations for DCT subsystem */
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| 27 |
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| 28 | #ifdef IDCT_SCALING_SUPPORTED
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| 29 |
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| 30 |
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| 31 | /*
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| 32 | * This module is specialized to the case DCTSIZE = 8.
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| 33 | */
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| 34 |
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| 35 | #if DCTSIZE != 8
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| 36 | Sorry, this code only copes with 8x8 DCTs. /* deliberate syntax err */
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| 37 | #endif
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| 38 |
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| 39 |
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| 40 | /* Scaling is the same as in jidctint.c. */
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| 41 |
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| 42 | #if BITS_IN_JSAMPLE == 8
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| 43 | #define CONST_BITS 13
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| 44 | #define PASS1_BITS 2
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| 45 | #else
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| 46 | #define CONST_BITS 13
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| 47 | #define PASS1_BITS 1 /* lose a little precision to avoid overflow */
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| 48 | #endif
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| 49 |
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| 50 | /* Some C compilers fail to reduce "FIX(constant)" at compile time, thus
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| 51 | * causing a lot of useless floating-point operations at run time.
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| 52 | * To get around this we use the following pre-calculated constants.
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| 53 | * If you change CONST_BITS you may want to add appropriate values.
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| 54 | * (With a reasonable C compiler, you can just rely on the FIX() macro...)
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| 55 | */
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| 56 |
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| 57 | #if CONST_BITS == 13
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| 58 | #define FIX_0_211164243 ((INT32) 1730) /* FIX(0.211164243) */
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| 59 | #define FIX_0_509795579 ((INT32) 4176) /* FIX(0.509795579) */
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| 60 | #define FIX_0_601344887 ((INT32) 4926) /* FIX(0.601344887) */
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| 61 | #define FIX_0_720959822 ((INT32) 5906) /* FIX(0.720959822) */
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| 62 | #define FIX_0_765366865 ((INT32) 6270) /* FIX(0.765366865) */
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| 63 | #define FIX_0_850430095 ((INT32) 6967) /* FIX(0.850430095) */
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| 64 | #define FIX_0_899976223 ((INT32) 7373) /* FIX(0.899976223) */
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| 65 | #define FIX_1_061594337 ((INT32) 8697) /* FIX(1.061594337) */
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| 66 | #define FIX_1_272758580 ((INT32) 10426) /* FIX(1.272758580) */
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| 67 | #define FIX_1_451774981 ((INT32) 11893) /* FIX(1.451774981) */
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| 68 | #define FIX_1_847759065 ((INT32) 15137) /* FIX(1.847759065) */
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| 69 | #define FIX_2_172734803 ((INT32) 17799) /* FIX(2.172734803) */
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| 70 | #define FIX_2_562915447 ((INT32) 20995) /* FIX(2.562915447) */
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| 71 | #define FIX_3_624509785 ((INT32) 29692) /* FIX(3.624509785) */
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| 72 | #else
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| 73 | #define FIX_0_211164243 FIX(0.211164243)
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| 74 | #define FIX_0_509795579 FIX(0.509795579)
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| 75 | #define FIX_0_601344887 FIX(0.601344887)
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| 76 | #define FIX_0_720959822 FIX(0.720959822)
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| 77 | #define FIX_0_765366865 FIX(0.765366865)
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| 78 | #define FIX_0_850430095 FIX(0.850430095)
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| 79 | #define FIX_0_899976223 FIX(0.899976223)
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| 80 | #define FIX_1_061594337 FIX(1.061594337)
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| 81 | #define FIX_1_272758580 FIX(1.272758580)
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| 82 | #define FIX_1_451774981 FIX(1.451774981)
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| 83 | #define FIX_1_847759065 FIX(1.847759065)
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| 84 | #define FIX_2_172734803 FIX(2.172734803)
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| 85 | #define FIX_2_562915447 FIX(2.562915447)
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| 86 | #define FIX_3_624509785 FIX(3.624509785)
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| 87 | #endif
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| 88 |
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| 89 |
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| 90 | /* Multiply an INT32 variable by an INT32 constant to yield an INT32 result.
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| 91 | * For 8-bit samples with the recommended scaling, all the variable
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| 92 | * and constant values involved are no more than 16 bits wide, so a
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| 93 | * 16x16->32 bit multiply can be used instead of a full 32x32 multiply.
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| 94 | * For 12-bit samples, a full 32-bit multiplication will be needed.
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| 95 | */
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| 96 |
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| 97 | #if BITS_IN_JSAMPLE == 8
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| 98 | #define MULTIPLY(var,const) MULTIPLY16C16(var,const)
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| 99 | #else
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| 100 | #define MULTIPLY(var,const) ((var) * (const))
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| 101 | #endif
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| 102 |
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| 103 |
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| 104 | /* Dequantize a coefficient by multiplying it by the multiplier-table
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| 105 | * entry; produce an int result. In this module, both inputs and result
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| 106 | * are 16 bits or less, so either int or short multiply will work.
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| 107 | */
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| 108 |
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| 109 | #define DEQUANTIZE(coef,quantval) (((ISLOW_MULT_TYPE) (coef)) * (quantval))
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| 110 |
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| 111 |
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| 112 | /*
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| 113 | * Perform dequantization and inverse DCT on one block of coefficients,
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| 114 | * producing a reduced-size 4x4 output block.
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| 115 | */
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| 116 |
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| 117 | GLOBAL(void)
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| 118 | jpeg_idct_4x4 (j_decompress_ptr cinfo, jpeg_component_info * compptr,
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| 119 | JCOEFPTR coef_block,
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| 120 | JSAMPARRAY output_buf, JDIMENSION output_col)
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| 121 | {
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| 122 | INT32 tmp0, tmp2, tmp10, tmp12;
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| 123 | INT32 z1, z2, z3, z4;
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| 124 | JCOEFPTR inptr;
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| 125 | ISLOW_MULT_TYPE * quantptr;
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| 126 | int * wsptr;
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| 127 | JSAMPROW outptr;
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| 128 | JSAMPLE *range_limit = IDCT_range_limit(cinfo);
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| 129 | int ctr;
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| 130 | int workspace[DCTSIZE*4]; /* buffers data between passes */
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| 131 | SHIFT_TEMPS
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| 132 |
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| 133 | /* Pass 1: process columns from input, store into work array. */
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| 134 |
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| 135 | inptr = coef_block;
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| 136 | quantptr = (ISLOW_MULT_TYPE *) compptr->dct_table;
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| 137 | wsptr = workspace;
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| 138 | for (ctr = DCTSIZE; ctr > 0; inptr++, quantptr++, wsptr++, ctr--) {
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| 139 | /* Don't bother to process column 4, because second pass won't use it */
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| 140 | if (ctr == DCTSIZE-4)
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| 141 | continue;
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| 142 | if (inptr[DCTSIZE*1] == 0 && inptr[DCTSIZE*2] == 0 &&
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| 143 | inptr[DCTSIZE*3] == 0 && inptr[DCTSIZE*5] == 0 &&
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| 144 | inptr[DCTSIZE*6] == 0 && inptr[DCTSIZE*7] == 0) {
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| 145 | /* AC terms all zero; we need not examine term 4 for 4x4 output */
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| 146 | int dcval = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]) << PASS1_BITS;
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| 147 |
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| 148 | wsptr[DCTSIZE*0] = dcval;
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| 149 | wsptr[DCTSIZE*1] = dcval;
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| 150 | wsptr[DCTSIZE*2] = dcval;
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| 151 | wsptr[DCTSIZE*3] = dcval;
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| 152 |
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| 153 | continue;
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| 154 | }
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| 155 |
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| 156 | /* Even part */
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| 157 |
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| 158 | tmp0 = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]);
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| 159 | tmp0 <<= (CONST_BITS+1);
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| 160 |
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| 161 | z2 = DEQUANTIZE(inptr[DCTSIZE*2], quantptr[DCTSIZE*2]);
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| 162 | z3 = DEQUANTIZE(inptr[DCTSIZE*6], quantptr[DCTSIZE*6]);
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| 163 |
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| 164 | tmp2 = MULTIPLY(z2, FIX_1_847759065) + MULTIPLY(z3, - FIX_0_765366865);
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| 165 |
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| 166 | tmp10 = tmp0 + tmp2;
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| 167 | tmp12 = tmp0 - tmp2;
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| 168 |
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| 169 | /* Odd part */
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| 170 |
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| 171 | z1 = DEQUANTIZE(inptr[DCTSIZE*7], quantptr[DCTSIZE*7]);
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| 172 | z2 = DEQUANTIZE(inptr[DCTSIZE*5], quantptr[DCTSIZE*5]);
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| 173 | z3 = DEQUANTIZE(inptr[DCTSIZE*3], quantptr[DCTSIZE*3]);
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| 174 | z4 = DEQUANTIZE(inptr[DCTSIZE*1], quantptr[DCTSIZE*1]);
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| 175 |
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| 176 | tmp0 = MULTIPLY(z1, - FIX_0_211164243) /* sqrt(2) * (c3-c1) */
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| 177 | + MULTIPLY(z2, FIX_1_451774981) /* sqrt(2) * (c3+c7) */
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| 178 | + MULTIPLY(z3, - FIX_2_172734803) /* sqrt(2) * (-c1-c5) */
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| 179 | + MULTIPLY(z4, FIX_1_061594337); /* sqrt(2) * (c5+c7) */
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| 180 |
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| 181 | tmp2 = MULTIPLY(z1, - FIX_0_509795579) /* sqrt(2) * (c7-c5) */
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| 182 | + MULTIPLY(z2, - FIX_0_601344887) /* sqrt(2) * (c5-c1) */
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| 183 | + MULTIPLY(z3, FIX_0_899976223) /* sqrt(2) * (c3-c7) */
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| 184 | + MULTIPLY(z4, FIX_2_562915447); /* sqrt(2) * (c1+c3) */
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| 185 |
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| 186 | /* Final output stage */
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| 187 |
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| 188 | wsptr[DCTSIZE*0] = (int) DESCALE(tmp10 + tmp2, CONST_BITS-PASS1_BITS+1);
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| 189 | wsptr[DCTSIZE*3] = (int) DESCALE(tmp10 - tmp2, CONST_BITS-PASS1_BITS+1);
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| 190 | wsptr[DCTSIZE*1] = (int) DESCALE(tmp12 + tmp0, CONST_BITS-PASS1_BITS+1);
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| 191 | wsptr[DCTSIZE*2] = (int) DESCALE(tmp12 - tmp0, CONST_BITS-PASS1_BITS+1);
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| 192 | }
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| 193 |
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| 194 | /* Pass 2: process 4 rows from work array, store into output array. */
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| 195 |
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| 196 | wsptr = workspace;
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| 197 | for (ctr = 0; ctr < 4; ctr++) {
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| 198 | outptr = output_buf[ctr] + output_col;
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| 199 | /* It's not clear whether a zero row test is worthwhile here ... */
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| 200 |
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| 201 | #ifndef NO_ZERO_ROW_TEST
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| 202 | if (wsptr[1] == 0 && wsptr[2] == 0 && wsptr[3] == 0 &&
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| 203 | wsptr[5] == 0 && wsptr[6] == 0 && wsptr[7] == 0) {
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| 204 | /* AC terms all zero */
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| 205 | JSAMPLE dcval = range_limit[(int) DESCALE((INT32) wsptr[0], PASS1_BITS+3)
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| 206 | & RANGE_MASK];
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| 207 |
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| 208 | outptr[0] = dcval;
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| 209 | outptr[1] = dcval;
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| 210 | outptr[2] = dcval;
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| 211 | outptr[3] = dcval;
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| 212 |
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| 213 | wsptr += DCTSIZE; /* advance pointer to next row */
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| 214 | continue;
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| 215 | }
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| 216 | #endif
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| 217 |
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| 218 | /* Even part */
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| 219 |
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| 220 | tmp0 = ((INT32) wsptr[0]) << (CONST_BITS+1);
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| 221 |
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| 222 | tmp2 = MULTIPLY((INT32) wsptr[2], FIX_1_847759065)
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| 223 | + MULTIPLY((INT32) wsptr[6], - FIX_0_765366865);
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| 224 |
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| 225 | tmp10 = tmp0 + tmp2;
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| 226 | tmp12 = tmp0 - tmp2;
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| 227 |
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| 228 | /* Odd part */
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| 229 |
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| 230 | z1 = (INT32) wsptr[7];
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| 231 | z2 = (INT32) wsptr[5];
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| 232 | z3 = (INT32) wsptr[3];
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| 233 | z4 = (INT32) wsptr[1];
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| 234 |
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| 235 | tmp0 = MULTIPLY(z1, - FIX_0_211164243) /* sqrt(2) * (c3-c1) */
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| 236 | + MULTIPLY(z2, FIX_1_451774981) /* sqrt(2) * (c3+c7) */
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| 237 | + MULTIPLY(z3, - FIX_2_172734803) /* sqrt(2) * (-c1-c5) */
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| 238 | + MULTIPLY(z4, FIX_1_061594337); /* sqrt(2) * (c5+c7) */
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| 239 |
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| 240 | tmp2 = MULTIPLY(z1, - FIX_0_509795579) /* sqrt(2) * (c7-c5) */
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| 241 | + MULTIPLY(z2, - FIX_0_601344887) /* sqrt(2) * (c5-c1) */
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| 242 | + MULTIPLY(z3, FIX_0_899976223) /* sqrt(2) * (c3-c7) */
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| 243 | + MULTIPLY(z4, FIX_2_562915447); /* sqrt(2) * (c1+c3) */
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| 244 |
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| 245 | /* Final output stage */
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| 246 |
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| 247 | outptr[0] = range_limit[(int) DESCALE(tmp10 + tmp2,
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| 248 | CONST_BITS+PASS1_BITS+3+1)
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| 249 | & RANGE_MASK];
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| 250 | outptr[3] = range_limit[(int) DESCALE(tmp10 - tmp2,
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| 251 | CONST_BITS+PASS1_BITS+3+1)
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| 252 | & RANGE_MASK];
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| 253 | outptr[1] = range_limit[(int) DESCALE(tmp12 + tmp0,
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| 254 | CONST_BITS+PASS1_BITS+3+1)
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| 255 | & RANGE_MASK];
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| 256 | outptr[2] = range_limit[(int) DESCALE(tmp12 - tmp0,
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| 257 | CONST_BITS+PASS1_BITS+3+1)
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| 258 | & RANGE_MASK];
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| 259 |
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| 260 | wsptr += DCTSIZE; /* advance pointer to next row */
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| 261 | }
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| 262 | }
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| 263 |
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| 264 |
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| 265 | /*
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| 266 | * Perform dequantization and inverse DCT on one block of coefficients,
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| 267 | * producing a reduced-size 2x2 output block.
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| 268 | */
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| 269 |
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| 270 | GLOBAL(void)
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| 271 | jpeg_idct_2x2 (j_decompress_ptr cinfo, jpeg_component_info * compptr,
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| 272 | JCOEFPTR coef_block,
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| 273 | JSAMPARRAY output_buf, JDIMENSION output_col)
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| 274 | {
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| 275 | INT32 tmp0, tmp10, z1;
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| 276 | JCOEFPTR inptr;
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| 277 | ISLOW_MULT_TYPE * quantptr;
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| 278 | int * wsptr;
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| 279 | JSAMPROW outptr;
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| 280 | JSAMPLE *range_limit = IDCT_range_limit(cinfo);
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| 281 | int ctr;
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| 282 | int workspace[DCTSIZE*2]; /* buffers data between passes */
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| 283 | SHIFT_TEMPS
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| 284 |
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| 285 | /* Pass 1: process columns from input, store into work array. */
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| 286 |
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| 287 | inptr = coef_block;
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| 288 | quantptr = (ISLOW_MULT_TYPE *) compptr->dct_table;
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| 289 | wsptr = workspace;
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| 290 | for (ctr = DCTSIZE; ctr > 0; inptr++, quantptr++, wsptr++, ctr--) {
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| 291 | /* Don't bother to process columns 2,4,6 */
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| 292 | if (ctr == DCTSIZE-2 || ctr == DCTSIZE-4 || ctr == DCTSIZE-6)
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| 293 | continue;
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| 294 | if (inptr[DCTSIZE*1] == 0 && inptr[DCTSIZE*3] == 0 &&
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| 295 | inptr[DCTSIZE*5] == 0 && inptr[DCTSIZE*7] == 0) {
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| 296 | /* AC terms all zero; we need not examine terms 2,4,6 for 2x2 output */
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| 297 | int dcval = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]) << PASS1_BITS;
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| 298 |
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| 299 | wsptr[DCTSIZE*0] = dcval;
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| 300 | wsptr[DCTSIZE*1] = dcval;
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| 301 |
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| 302 | continue;
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| 303 | }
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| 304 |
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| 305 | /* Even part */
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| 306 |
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| 307 | z1 = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]);
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| 308 | tmp10 = z1 << (CONST_BITS+2);
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| 309 |
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| 310 | /* Odd part */
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| 311 |
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| 312 | z1 = DEQUANTIZE(inptr[DCTSIZE*7], quantptr[DCTSIZE*7]);
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| 313 | tmp0 = MULTIPLY(z1, - FIX_0_720959822); /* sqrt(2) * (c7-c5+c3-c1) */
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| 314 | z1 = DEQUANTIZE(inptr[DCTSIZE*5], quantptr[DCTSIZE*5]);
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| 315 | tmp0 += MULTIPLY(z1, FIX_0_850430095); /* sqrt(2) * (-c1+c3+c5+c7) */
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| 316 | z1 = DEQUANTIZE(inptr[DCTSIZE*3], quantptr[DCTSIZE*3]);
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| 317 | tmp0 += MULTIPLY(z1, - FIX_1_272758580); /* sqrt(2) * (-c1+c3-c5-c7) */
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| 318 | z1 = DEQUANTIZE(inptr[DCTSIZE*1], quantptr[DCTSIZE*1]);
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| 319 | tmp0 += MULTIPLY(z1, FIX_3_624509785); /* sqrt(2) * (c1+c3+c5+c7) */
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| 320 |
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| 321 | /* Final output stage */
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| 322 |
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| 323 | wsptr[DCTSIZE*0] = (int) DESCALE(tmp10 + tmp0, CONST_BITS-PASS1_BITS+2);
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| 324 | wsptr[DCTSIZE*1] = (int) DESCALE(tmp10 - tmp0, CONST_BITS-PASS1_BITS+2);
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| 325 | }
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| 326 |
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| 327 | /* Pass 2: process 2 rows from work array, store into output array. */
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| 328 |
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| 329 | wsptr = workspace;
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| 330 | for (ctr = 0; ctr < 2; ctr++) {
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| 331 | outptr = output_buf[ctr] + output_col;
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| 332 | /* It's not clear whether a zero row test is worthwhile here ... */
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| 333 |
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| 334 | #ifndef NO_ZERO_ROW_TEST
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| 335 | if (wsptr[1] == 0 && wsptr[3] == 0 && wsptr[5] == 0 && wsptr[7] == 0) {
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| 336 | /* AC terms all zero */
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| 337 | JSAMPLE dcval = range_limit[(int) DESCALE((INT32) wsptr[0], PASS1_BITS+3)
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| 338 | & RANGE_MASK];
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| 339 |
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| 340 | outptr[0] = dcval;
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| 341 | outptr[1] = dcval;
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| 342 |
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| 343 | wsptr += DCTSIZE; /* advance pointer to next row */
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| 344 | continue;
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| 345 | }
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| 346 | #endif
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| 347 |
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| 348 | /* Even part */
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| 349 |
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| 350 | tmp10 = ((INT32) wsptr[0]) << (CONST_BITS+2);
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| 351 |
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| 352 | /* Odd part */
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| 353 |
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| 354 | tmp0 = MULTIPLY((INT32) wsptr[7], - FIX_0_720959822) /* sqrt(2) * (c7-c5+c3-c1) */
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| 355 | + MULTIPLY((INT32) wsptr[5], FIX_0_850430095) /* sqrt(2) * (-c1+c3+c5+c7) */
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| 356 | + MULTIPLY((INT32) wsptr[3], - FIX_1_272758580) /* sqrt(2) * (-c1+c3-c5-c7) */
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| 357 | + MULTIPLY((INT32) wsptr[1], FIX_3_624509785); /* sqrt(2) * (c1+c3+c5+c7) */
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| 358 |
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| 359 | /* Final output stage */
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| 360 |
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| 361 | outptr[0] = range_limit[(int) DESCALE(tmp10 + tmp0,
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| 362 | CONST_BITS+PASS1_BITS+3+2)
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| 363 | & RANGE_MASK];
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| 364 | outptr[1] = range_limit[(int) DESCALE(tmp10 - tmp0,
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| 365 | CONST_BITS+PASS1_BITS+3+2)
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| 366 | & RANGE_MASK];
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| 367 |
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| 368 | wsptr += DCTSIZE; /* advance pointer to next row */
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| 369 | }
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| 370 | }
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| 371 |
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| 372 |
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| 373 | /*
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| 374 | * Perform dequantization and inverse DCT on one block of coefficients,
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| 375 | * producing a reduced-size 1x1 output block.
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| 376 | */
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| 377 |
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| 378 | GLOBAL(void)
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| 379 | jpeg_idct_1x1 (j_decompress_ptr cinfo, jpeg_component_info * compptr,
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| 380 | JCOEFPTR coef_block,
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| 381 | JSAMPARRAY output_buf, JDIMENSION output_col)
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| 382 | {
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| 383 | int dcval;
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| 384 | ISLOW_MULT_TYPE * quantptr;
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| 385 | JSAMPLE *range_limit = IDCT_range_limit(cinfo);
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| 386 | SHIFT_TEMPS
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| 387 |
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| 388 | /* We hardly need an inverse DCT routine for this: just take the
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| 389 | * average pixel value, which is one-eighth of the DC coefficient.
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| 390 | */
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| 391 | quantptr = (ISLOW_MULT_TYPE *) compptr->dct_table;
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| 392 | dcval = DEQUANTIZE(coef_block[0], quantptr[0]);
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| 393 | dcval = (int) DESCALE((INT32) dcval, 3);
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| 394 |
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| 395 | output_buf[0][output_col] = range_limit[dcval & RANGE_MASK];
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| 396 | }
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| 397 |
|
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| 398 | #endif /* IDCT_SCALING_SUPPORTED */
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