www.pudn.com > imgport.rar > jidctred.c, change:2008-11-05,size:14086b


/* 
 * jidctred.c 
 * 
 * Copyright (C) 1994-1998, 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 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  ((JPEG_INT32)  1730)	/* FIX(0.211164243) */ 
#define FIX_0_509795579  ((JPEG_INT32)  4176)	/* FIX(0.509795579) */ 
#define FIX_0_601344887  ((JPEG_INT32)  4926)	/* FIX(0.601344887) */ 
#define FIX_0_720959822  ((JPEG_INT32)  5906)	/* FIX(0.720959822) */ 
#define FIX_0_765366865  ((JPEG_INT32)  6270)	/* FIX(0.765366865) */ 
#define FIX_0_850430095  ((JPEG_INT32)  6967)	/* FIX(0.850430095) */ 
#define FIX_0_899976223  ((JPEG_INT32)  7373)	/* FIX(0.899976223) */ 
#define FIX_1_061594337  ((JPEG_INT32)  8697)	/* FIX(1.061594337) */ 
#define FIX_1_272758580  ((JPEG_INT32)  10426)	/* FIX(1.272758580) */ 
#define FIX_1_451774981  ((JPEG_INT32)  11893)	/* FIX(1.451774981) */ 
#define FIX_1_847759065  ((JPEG_INT32)  15137)	/* FIX(1.847759065) */ 
#define FIX_2_172734803  ((JPEG_INT32)  17799)	/* FIX(2.172734803) */ 
#define FIX_2_562915447  ((JPEG_INT32)  20995)	/* FIX(2.562915447) */ 
#define FIX_3_624509785  ((JPEG_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) 
{ 
  JPEG_INT32 tmp0, tmp2, tmp10, tmp12; 
  JPEG_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] == 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 = 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] == 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((JPEG_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 = ((JPEG_INT32) wsptr[0]) << (CONST_BITS+1); 
     
    tmp2 = MULTIPLY((JPEG_INT32) wsptr[2], FIX_1_847759065) 
	 + MULTIPLY((JPEG_INT32) wsptr[6], - FIX_0_765366865); 
     
    tmp10 = tmp0 + tmp2; 
    tmp12 = tmp0 - tmp2; 
     
    /* Odd part */ 
     
    z1 = (JPEG_INT32) wsptr[7]; 
    z2 = (JPEG_INT32) wsptr[5]; 
    z3 = (JPEG_INT32) wsptr[3]; 
    z4 = (JPEG_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) 
{ 
  JPEG_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] == 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 = 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] == 0 && wsptr[3] == 0 && wsptr[5] == 0 && wsptr[7] == 0) { 
      /* AC terms all zero */ 
      JSAMPLE dcval = range_limit[(int) DESCALE((JPEG_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 = ((JPEG_INT32) wsptr[0]) << (CONST_BITS+2); 
     
    /* Odd part */ 
 
    tmp0 = MULTIPLY((JPEG_INT32) wsptr[7], - FIX_0_720959822) /* sqrt(2) * (c7-c5+c3-c1) */ 
	 + MULTIPLY((JPEG_INT32) wsptr[5], FIX_0_850430095) /* sqrt(2) * (-c1+c3+c5+c7) */ 
	 + MULTIPLY((JPEG_INT32) wsptr[3], - FIX_1_272758580) /* sqrt(2) * (-c1+c3-c5-c7) */ 
	 + MULTIPLY((JPEG_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((JPEG_INT32) dcval, 3); 
 
  output_buf[0][output_col] = range_limit[dcval & RANGE_MASK]; 
} 
 
#endif /* IDCT_SCALING_SUPPORTED */