/* * jidctred.c * * This file was part of the Independent JPEG Group's software: * Copyright (C) 1994-1998, Thomas G. Lane. * libjpeg-turbo Modifications: * Copyright (C) 2015, 2022, D. R. Commander. * For conditions of distribution and use, see the accompanying README.ijg * 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 8x8 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 ((JLONG)1730) /* FIX(0.211164243) */ #define FIX_0_509795579 ((JLONG)4176) /* FIX(0.509795579) */ #define FIX_0_601344887 ((JLONG)4926) /* FIX(0.601344887) */ #define FIX_0_720959822 ((JLONG)5906) /* FIX(0.720959822) */ #define FIX_0_765366865 ((JLONG)6270) /* FIX(0.765366865) */ #define FIX_0_850430095 ((JLONG)6967) /* FIX(0.850430095) */ #define FIX_0_899976223 ((JLONG)7373) /* FIX(0.899976223) */ #define FIX_1_061594337 ((JLONG)8697) /* FIX(1.061594337) */ #define FIX_1_272758580 ((JLONG)10426) /* FIX(1.272758580) */ #define FIX_1_451774981 ((JLONG)11893) /* FIX(1.451774981) */ #define FIX_1_847759065 ((JLONG)15137) /* FIX(1.847759065) */ #define FIX_2_172734803 ((JLONG)17799) /* FIX(2.172734803) */ #define FIX_2_562915447 ((JLONG)20995) /* FIX(2.562915447) */ #define FIX_3_624509785 ((JLONG)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 a JLONG variable by a JLONG constant to yield a JLONG 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) { JLONG tmp0, tmp2, tmp10, tmp12; JLONG 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] == 0 && inptr[DCTSIZE * 2] == 0 && inptr[DCTSIZE * 3] == 0 && inptr[DCTSIZE * 5] == 0 && inptr[DCTSIZE * 6] == 0 && inptr[DCTSIZE * 7] == 0) { /* AC terms all zero; we need not examine term 4 for 4x4 output */ int dcval = LEFT_SHIFT(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 = LEFT_SHIFT(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] == 0 && wsptr[2] == 0 && wsptr[3] == 0 && wsptr[5] == 0 && wsptr[6] == 0 && wsptr[7] == 0) { /* AC terms all zero */ _JSAMPLE dcval = range_limit[(int)DESCALE((JLONG)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 = LEFT_SHIFT((JLONG)wsptr[0], CONST_BITS + 1); tmp2 = MULTIPLY((JLONG)wsptr[2], FIX_1_847759065) + MULTIPLY((JLONG)wsptr[6], -FIX_0_765366865); tmp10 = tmp0 + tmp2; tmp12 = tmp0 - tmp2; /* Odd part */ z1 = (JLONG)wsptr[7]; z2 = (JLONG)wsptr[5]; z3 = (JLONG)wsptr[3]; z4 = (JLONG)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) { JLONG 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] == 0 && inptr[DCTSIZE * 3] == 0 && inptr[DCTSIZE * 5] == 0 && inptr[DCTSIZE * 7] == 0) { /* AC terms all zero; we need not examine terms 2,4,6 for 2x2 output */ int dcval = LEFT_SHIFT(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 = LEFT_SHIFT(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] == 0 && wsptr[3] == 0 && wsptr[5] == 0 && wsptr[7] == 0) { /* AC terms all zero */ _JSAMPLE dcval = range_limit[(int)DESCALE((JLONG)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 = LEFT_SHIFT((JLONG)wsptr[0], CONST_BITS + 2); /* Odd part */ tmp0 = MULTIPLY((JLONG)wsptr[7], -FIX_0_720959822) + /* sqrt(2) * ( c7-c5+c3-c1) */ MULTIPLY((JLONG)wsptr[5], FIX_0_850430095) + /* sqrt(2) * (-c1+c3+c5+c7) */ MULTIPLY((JLONG)wsptr[3], -FIX_1_272758580) + /* sqrt(2) * (-c1+c3-c5-c7) */ MULTIPLY((JLONG)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((JLONG)dcval, 3); output_buf[0][output_col] = range_limit[dcval & RANGE_MASK]; } #endif /* IDCT_SCALING_SUPPORTED */