/* * jidctred.c * * Copyright (C) 1994, Thomas G. Lane. * This file is part of the Independent JPEG Group's software. * For conditions of distribution and use, see the accompanying README file. * * This file contains inverse-DCT routines that produce reduced-size output: * either 4x4, 2x2, or 1x1 pixels from an 8x8 DCT block. * * The implementation is based on the Loeffler, Ligtenberg and Moschytz (LL&M) * algorithm used in jidctint.c. We simply replace each 8-to-8 1-D IDCT step * with an 8-to-4 step that produces the four averages of two adjacent outputs * (or an 8-to-2 step producing two averages of four outputs, for 2x2 output). * These steps were derived by computing the corresponding values at the end * of the normal LL&M code, then simplifying as much as possible. * * 1x1 is trivial: just take the DC coefficient divided by 8. * * See jidctint.c for additional comments. */ #define JPEG_INTERNALS #include "jinclude.h" #include "jpeglib.h" #include "jdct.h" /* Private declarations for DCT subsystem */ #ifdef IDCT_SCALING_SUPPORTED /* * This module is specialized to the case DCTSIZE = 8. */ #if DCTSIZE != 8 Sorry, this code only copes with 8 x8 DCTs. /* deliberate syntax err */ #endif /* Scaling is the same as in jidctint.c. */ #if BITS_IN_JSAMPLE == 8 #define CONST_BITS 13 #define PASS1_BITS 2 #else #define CONST_BITS 13 #define PASS1_BITS 1 /* lose a little precision to avoid overflow */ #endif /* Some C compilers fail to reduce "FIX(constant)" at compile time, thus * causing a lot of useless floating-point operations at run time. * To get around this we use the following pre-calculated constants. * If you change CONST_BITS you may want to add appropriate values. * (With a reasonable C compiler, you can just rely on the FIX() macro...) */ #if CONST_BITS == 13 #define FIX_0_211164243 ( (INT32) 1730 ) /* FIX(0.211164243) */ #define FIX_0_509795579 ( (INT32) 4176 ) /* FIX(0.509795579) */ #define FIX_0_601344887 ( (INT32) 4926 ) /* FIX(0.601344887) */ #define FIX_0_720959822 ( (INT32) 5906 ) /* FIX(0.720959822) */ #define FIX_0_765366865 ( (INT32) 6270 ) /* FIX(0.765366865) */ #define FIX_0_850430095 ( (INT32) 6967 ) /* FIX(0.850430095) */ #define FIX_0_899976223 ( (INT32) 7373 ) /* FIX(0.899976223) */ #define FIX_1_061594337 ( (INT32) 8697 ) /* FIX(1.061594337) */ #define FIX_1_272758580 ( (INT32) 10426 ) /* FIX(1.272758580) */ #define FIX_1_451774981 ( (INT32) 11893 ) /* FIX(1.451774981) */ #define FIX_1_847759065 ( (INT32) 15137 ) /* FIX(1.847759065) */ #define FIX_2_172734803 ( (INT32) 17799 ) /* FIX(2.172734803) */ #define FIX_2_562915447 ( (INT32) 20995 ) /* FIX(2.562915447) */ #define FIX_3_624509785 ( (INT32) 29692 ) /* FIX(3.624509785) */ #else #define FIX_0_211164243 FIX( 0.211164243 ) #define FIX_0_509795579 FIX( 0.509795579 ) #define FIX_0_601344887 FIX( 0.601344887 ) #define FIX_0_720959822 FIX( 0.720959822 ) #define FIX_0_765366865 FIX( 0.765366865 ) #define FIX_0_850430095 FIX( 0.850430095 ) #define FIX_0_899976223 FIX( 0.899976223 ) #define FIX_1_061594337 FIX( 1.061594337 ) #define FIX_1_272758580 FIX( 1.272758580 ) #define FIX_1_451774981 FIX( 1.451774981 ) #define FIX_1_847759065 FIX( 1.847759065 ) #define FIX_2_172734803 FIX( 2.172734803 ) #define FIX_2_562915447 FIX( 2.562915447 ) #define FIX_3_624509785 FIX( 3.624509785 ) #endif /* Multiply an INT32 variable by an INT32 constant to yield an INT32 result. * For 8-bit samples with the recommended scaling, all the variable * and constant values involved are no more than 16 bits wide, so a * 16x16->32 bit multiply can be used instead of a full 32x32 multiply. * For 12-bit samples, a full 32-bit multiplication will be needed. */ #if BITS_IN_JSAMPLE == 8 #define MULTIPLY( var, const ) MULTIPLY16C16( var, const ) #else #define MULTIPLY( var, const ) ( ( var ) * ( const ) ) #endif /* Dequantize a coefficient by multiplying it by the multiplier-table * entry; produce an int result. In this module, both inputs and result * are 16 bits or less, so either int or short multiply will work. */ #define DEQUANTIZE( coef, quantval ) ( ( (ISLOW_MULT_TYPE) ( coef ) ) * ( quantval ) ) /* * Perform dequantization and inverse DCT on one block of coefficients, * producing a reduced-size 4x4 output block. */ GLOBAL void jpeg_idct_4x4( j_decompress_ptr cinfo, jpeg_component_info * compptr, JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col ) { INT32 tmp0, tmp2, tmp10, tmp12; INT32 z1, z2, z3, z4; JCOEFPTR inptr; ISLOW_MULT_TYPE * quantptr; int * wsptr; JSAMPROW outptr; JSAMPLE * range_limit = IDCT_range_limit( cinfo ); int ctr; int workspace[DCTSIZE * 4];/* buffers data between passes */ SHIFT_TEMPS /* Pass 1: process columns from input, store into work array. */ inptr = coef_block; quantptr = (ISLOW_MULT_TYPE *) compptr->dct_table; wsptr = workspace; for ( ctr = DCTSIZE; ctr > 0; inptr++, quantptr++, wsptr++, ctr-- ) { /* Don't bother to process column 4, because second pass won't use it */ if ( ctr == DCTSIZE - 4 ) { continue; } if ( ( inptr[DCTSIZE * 1] | inptr[DCTSIZE * 2] | inptr[DCTSIZE * 3] | inptr[DCTSIZE * 5] | inptr[DCTSIZE * 6] | inptr[DCTSIZE * 7] ) == 0 ) { /* AC terms all zero; we need not examine term 4 for 4x4 output */ int dcval = DEQUANTIZE( inptr[DCTSIZE * 0], quantptr[DCTSIZE * 0] ) << PASS1_BITS; wsptr[DCTSIZE * 0] = dcval; wsptr[DCTSIZE * 1] = dcval; wsptr[DCTSIZE * 2] = dcval; wsptr[DCTSIZE * 3] = dcval; continue; } /* Even part */ tmp0 = DEQUANTIZE( inptr[DCTSIZE * 0], quantptr[DCTSIZE * 0] ); tmp0 <<= ( CONST_BITS + 1 ); z2 = DEQUANTIZE( inptr[DCTSIZE * 2], quantptr[DCTSIZE * 2] ); z3 = DEQUANTIZE( inptr[DCTSIZE * 6], quantptr[DCTSIZE * 6] ); tmp2 = MULTIPLY( z2, FIX_1_847759065 ) + MULTIPLY( z3, -FIX_0_765366865 ); tmp10 = tmp0 + tmp2; tmp12 = tmp0 - tmp2; /* Odd part */ z1 = DEQUANTIZE( inptr[DCTSIZE * 7], quantptr[DCTSIZE * 7] ); z2 = DEQUANTIZE( inptr[DCTSIZE * 5], quantptr[DCTSIZE * 5] ); z3 = DEQUANTIZE( inptr[DCTSIZE * 3], quantptr[DCTSIZE * 3] ); z4 = DEQUANTIZE( inptr[DCTSIZE * 1], quantptr[DCTSIZE * 1] ); tmp0 = MULTIPLY( z1, -FIX_0_211164243 )/* sqrt(2) * (c3-c1) */ + MULTIPLY( z2, FIX_1_451774981 )/* sqrt(2) * (c3+c7) */ + MULTIPLY( z3, -FIX_2_172734803 )/* sqrt(2) * (-c1-c5) */ + MULTIPLY( z4, FIX_1_061594337 );/* sqrt(2) * (c5+c7) */ tmp2 = MULTIPLY( z1, -FIX_0_509795579 )/* sqrt(2) * (c7-c5) */ + MULTIPLY( z2, -FIX_0_601344887 )/* sqrt(2) * (c5-c1) */ + MULTIPLY( z3, FIX_0_899976223 )/* sqrt(2) * (c3-c7) */ + MULTIPLY( z4, FIX_2_562915447 );/* sqrt(2) * (c1+c3) */ /* Final output stage */ wsptr[DCTSIZE * 0] = (int) DESCALE( tmp10 + tmp2, CONST_BITS - PASS1_BITS + 1 ); wsptr[DCTSIZE * 3] = (int) DESCALE( tmp10 - tmp2, CONST_BITS - PASS1_BITS + 1 ); wsptr[DCTSIZE * 1] = (int) DESCALE( tmp12 + tmp0, CONST_BITS - PASS1_BITS + 1 ); wsptr[DCTSIZE * 2] = (int) DESCALE( tmp12 - tmp0, CONST_BITS - PASS1_BITS + 1 ); } /* Pass 2: process 4 rows from work array, store into output array. */ wsptr = workspace; for ( ctr = 0; ctr < 4; ctr++ ) { outptr = output_buf[ctr] + output_col; /* It's not clear whether a zero row test is worthwhile here ... */ #ifndef NO_ZERO_ROW_TEST if ( ( wsptr[1] | wsptr[2] | wsptr[3] | wsptr[5] | wsptr[6] | wsptr[7] ) == 0 ) { /* AC terms all zero */ JSAMPLE dcval = range_limit[(int) DESCALE( (INT32) wsptr[0], PASS1_BITS + 3 ) & RANGE_MASK]; outptr[0] = dcval; outptr[1] = dcval; outptr[2] = dcval; outptr[3] = dcval; wsptr += DCTSIZE;/* advance pointer to next row */ continue; } #endif /* Even part */ tmp0 = ( (INT32) wsptr[0] ) << ( CONST_BITS + 1 ); tmp2 = MULTIPLY( (INT32) wsptr[2], FIX_1_847759065 ) + MULTIPLY( (INT32) wsptr[6], -FIX_0_765366865 ); tmp10 = tmp0 + tmp2; tmp12 = tmp0 - tmp2; /* Odd part */ z1 = (INT32) wsptr[7]; z2 = (INT32) wsptr[5]; z3 = (INT32) wsptr[3]; z4 = (INT32) wsptr[1]; tmp0 = MULTIPLY( z1, -FIX_0_211164243 )/* sqrt(2) * (c3-c1) */ + MULTIPLY( z2, FIX_1_451774981 )/* sqrt(2) * (c3+c7) */ + MULTIPLY( z3, -FIX_2_172734803 )/* sqrt(2) * (-c1-c5) */ + MULTIPLY( z4, FIX_1_061594337 );/* sqrt(2) * (c5+c7) */ tmp2 = MULTIPLY( z1, -FIX_0_509795579 )/* sqrt(2) * (c7-c5) */ + MULTIPLY( z2, -FIX_0_601344887 )/* sqrt(2) * (c5-c1) */ + MULTIPLY( z3, FIX_0_899976223 )/* sqrt(2) * (c3-c7) */ + MULTIPLY( z4, FIX_2_562915447 );/* sqrt(2) * (c1+c3) */ /* Final output stage */ outptr[0] = range_limit[(int) DESCALE( tmp10 + tmp2, CONST_BITS + PASS1_BITS + 3 + 1 ) & RANGE_MASK]; outptr[3] = range_limit[(int) DESCALE( tmp10 - tmp2, CONST_BITS + PASS1_BITS + 3 + 1 ) & RANGE_MASK]; outptr[1] = range_limit[(int) DESCALE( tmp12 + tmp0, CONST_BITS + PASS1_BITS + 3 + 1 ) & RANGE_MASK]; outptr[2] = range_limit[(int) DESCALE( tmp12 - tmp0, CONST_BITS + PASS1_BITS + 3 + 1 ) & RANGE_MASK]; wsptr += DCTSIZE; /* advance pointer to next row */ } } /* * Perform dequantization and inverse DCT on one block of coefficients, * producing a reduced-size 2x2 output block. */ GLOBAL void jpeg_idct_2x2( j_decompress_ptr cinfo, jpeg_component_info * compptr, JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col ) { INT32 tmp0, tmp10, z1; JCOEFPTR inptr; ISLOW_MULT_TYPE * quantptr; int * wsptr; JSAMPROW outptr; JSAMPLE * range_limit = IDCT_range_limit( cinfo ); int ctr; int workspace[DCTSIZE * 2];/* buffers data between passes */ SHIFT_TEMPS /* Pass 1: process columns from input, store into work array. */ inptr = coef_block; quantptr = (ISLOW_MULT_TYPE *) compptr->dct_table; wsptr = workspace; for ( ctr = DCTSIZE; ctr > 0; inptr++, quantptr++, wsptr++, ctr-- ) { /* Don't bother to process columns 2,4,6 */ if ( ( ctr == DCTSIZE - 2 ) || ( ctr == DCTSIZE - 4 ) || ( ctr == DCTSIZE - 6 ) ) { continue; } if ( ( inptr[DCTSIZE * 1] | inptr[DCTSIZE * 3] | inptr[DCTSIZE * 5] | inptr[DCTSIZE * 7] ) == 0 ) { /* AC terms all zero; we need not examine terms 2,4,6 for 2x2 output */ int dcval = DEQUANTIZE( inptr[DCTSIZE * 0], quantptr[DCTSIZE * 0] ) << PASS1_BITS; wsptr[DCTSIZE * 0] = dcval; wsptr[DCTSIZE * 1] = dcval; continue; } /* Even part */ z1 = DEQUANTIZE( inptr[DCTSIZE * 0], quantptr[DCTSIZE * 0] ); tmp10 = z1 << ( CONST_BITS + 2 ); /* Odd part */ z1 = DEQUANTIZE( inptr[DCTSIZE * 7], quantptr[DCTSIZE * 7] ); tmp0 = MULTIPLY( z1, -FIX_0_720959822 );/* sqrt(2) * (c7-c5+c3-c1) */ z1 = DEQUANTIZE( inptr[DCTSIZE * 5], quantptr[DCTSIZE * 5] ); tmp0 += MULTIPLY( z1, FIX_0_850430095 );/* sqrt(2) * (-c1+c3+c5+c7) */ z1 = DEQUANTIZE( inptr[DCTSIZE * 3], quantptr[DCTSIZE * 3] ); tmp0 += MULTIPLY( z1, -FIX_1_272758580 );/* sqrt(2) * (-c1+c3-c5-c7) */ z1 = DEQUANTIZE( inptr[DCTSIZE * 1], quantptr[DCTSIZE * 1] ); tmp0 += MULTIPLY( z1, FIX_3_624509785 );/* sqrt(2) * (c1+c3+c5+c7) */ /* Final output stage */ wsptr[DCTSIZE * 0] = (int) DESCALE( tmp10 + tmp0, CONST_BITS - PASS1_BITS + 2 ); wsptr[DCTSIZE * 1] = (int) DESCALE( tmp10 - tmp0, CONST_BITS - PASS1_BITS + 2 ); } /* Pass 2: process 2 rows from work array, store into output array. */ wsptr = workspace; for ( ctr = 0; ctr < 2; ctr++ ) { outptr = output_buf[ctr] + output_col; /* It's not clear whether a zero row test is worthwhile here ... */ #ifndef NO_ZERO_ROW_TEST if ( ( wsptr[1] | wsptr[3] | wsptr[5] | wsptr[7] ) == 0 ) { /* AC terms all zero */ JSAMPLE dcval = range_limit[(int) DESCALE( (INT32) wsptr[0], PASS1_BITS + 3 ) & RANGE_MASK]; outptr[0] = dcval; outptr[1] = dcval; wsptr += DCTSIZE;/* advance pointer to next row */ continue; } #endif /* Even part */ tmp10 = ( (INT32) wsptr[0] ) << ( CONST_BITS + 2 ); /* Odd part */ tmp0 = MULTIPLY( (INT32) wsptr[7], -FIX_0_720959822 )/* sqrt(2) * (c7-c5+c3-c1) */ + MULTIPLY( (INT32) wsptr[5], FIX_0_850430095 )/* sqrt(2) * (-c1+c3+c5+c7) */ + MULTIPLY( (INT32) wsptr[3], -FIX_1_272758580 )/* sqrt(2) * (-c1+c3-c5-c7) */ + MULTIPLY( (INT32) wsptr[1], FIX_3_624509785 );/* sqrt(2) * (c1+c3+c5+c7) */ /* Final output stage */ outptr[0] = range_limit[(int) DESCALE( tmp10 + tmp0, CONST_BITS + PASS1_BITS + 3 + 2 ) & RANGE_MASK]; outptr[1] = range_limit[(int) DESCALE( tmp10 - tmp0, CONST_BITS + PASS1_BITS + 3 + 2 ) & RANGE_MASK]; wsptr += DCTSIZE; /* advance pointer to next row */ } } /* * Perform dequantization and inverse DCT on one block of coefficients, * producing a reduced-size 1x1 output block. */ GLOBAL void jpeg_idct_1x1( j_decompress_ptr cinfo, jpeg_component_info * compptr, JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col ) { int dcval; ISLOW_MULT_TYPE * quantptr; JSAMPLE * range_limit = IDCT_range_limit( cinfo ); SHIFT_TEMPS /* We hardly need an inverse DCT routine for this: just take the * average pixel value, which is one-eighth of the DC coefficient. */ quantptr = (ISLOW_MULT_TYPE *) compptr->dct_table; dcval = DEQUANTIZE( coef_block[0], quantptr[0] ); dcval = (int) DESCALE( (INT32) dcval, 3 ); output_buf[0][output_col] = range_limit[dcval & RANGE_MASK]; } #endif /* IDCT_SCALING_SUPPORTED */