libjpeg9c的VC2017静态库工程

/* * jidctint.c * * Copyright (C) 1991-1998, Thomas G. Lane. * Modification developed 2002-2016 by Guido Vollbeding. * 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 a slow-but-accurate integer implementation of the * inverse DCT (Discrete Cosine Transform). In the IJG code, this routine * must also perform dequantization of the input coefficients. * * A 2-D IDCT can be done by 1-D IDCT on each column followed by 1-D IDCT * on each row (or vice versa, but it's more convenient to emit a row at * a time). Direct algorithms are also available, but they are much more * complex and seem not to be any faster when reduced to code. * * This implementation is based on an algorithm described in * C. Loeffler, A. Ligtenberg and G. Moschytz, "Practical Fast 1-D DCT * Algorithms with 11 Multiplications", Proc. Int'l. Conf. on Acoustics, * Speech, and Signal Processing 1989 (ICASSP '89), pp. 988-991. * The primary algorithm described there uses 11 multiplies and 29 adds. * We use their alternate method with 12 multiplies and 32 adds. * The advantage of this method is that no data path contains more than one * multiplication; this allows a very simple and accurate implementation in * scaled fixed-point arithmetic, with a minimal number of shifts. * * We also provide IDCT routines with various output sample block sizes for * direct resolution reduction or enlargement and for direct resolving the * common 2x1 and 1x2 subsampling cases without additional resampling: NxN * (N=1...16), 2NxN, and Nx2N (N=1...8) pixels for one 8x8 input DCT block. * * For N<8 we simply take the corresponding low-frequency coefficients of * the 8x8 input DCT block and apply an NxN point IDCT on the sub-block * to yield the downscaled outputs. * This can be seen as direct low-pass downsampling from the DCT domain * point of view rather than the usual spatial domain point of view, * yielding significant computational savings and results at least * as good as common bilinear (averaging) spatial downsampling. * * For N>8 we apply a partial NxN IDCT on the 8 input coefficients as * lower frequencies and higher frequencies assumed to be zero. * It turns out that the computational effort is similar to the 8x8 IDCT * regarding the output size. * Furthermore, the scaling and descaling is the same for all IDCT sizes. * * CAUTION: We rely on the FIX() macro except for the N=1,2,4,8 cases * since there would be too many additional constants to pre-calculate. */ #define JPEG_INTERNALS #include "jinclude.h" #include "jpeglib.h" #include "jdct.h" /* Private declarations for DCT subsystem */ #ifdef DCT_ISLOW_SUPPORTED /* * This module is specialized to the case DCTSIZE = 8. */ #if DCTSIZE != 8 Sorry, this code only copes with 8x8 DCT blocks. /* deliberate syntax err */ #endif /* * The poop on this scaling stuff is as follows: * * Each 1-D IDCT step produces outputs which are a factor of sqrt(N) * larger than the true IDCT outputs. The final outputs are therefore * a factor of N larger than desired; since N=8 this can be cured by * a simple right shift at the end of the algorithm. The advantage of * this arrangement is that we save two multiplications per 1-D IDCT, * because the y0 and y4 inputs need not be divided by sqrt(N). * * We have to do addition and subtraction of the integer inputs, which * is no problem, and multiplication by fractional constants, which is * a problem to do in integer arithmetic. We multiply all the constants * by CONST_SCALE and convert them to integer constants (thus retaining * CONST_BITS bits of precision in the constants). After doing a * multiplication we have to divide the product by CONST_SCALE, with proper * rounding, to produce the correct output. This division can be done * cheaply as a right shift of CONST_BITS bits. We postpone shifting * as long as possible so that partial sums can be added together with * full fractional precision. * * The outputs of the first pass are scaled up by PASS1_BITS bits so that * they are represented to better-than-integral precision. These outputs * require BITS_IN_JSAMPLE + PASS1_BITS + 3 bits; this fits in a 16-bit word * with the recommended scaling. (To scale up 12-bit sample data further, an * intermediate INT32 array would be needed.) * * To avoid overflow of the 32-bit intermediate results in pass 2, we must * have BITS_IN_JSAMPLE + CONST_BITS + PASS1_BITS <= 26. Error analysis * shows that the values given below are the most effective. */ #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_298631336 ((INT32) 2446) /* FIX(0.298631336) */ #define FIX_0_390180644 ((INT32) 3196) /* FIX(0.390180644) */ #define FIX_0_541196100 ((INT32) 4433) /* FIX(0.541196100) */ #define FIX_0_765366865 ((INT32) 6270) /* FIX(0.765366865) */ #define FIX_0_899976223 ((INT32) 7373) /* FIX(0.899976223) */ #define FIX_1_175875602 ((INT32) 9633) /* FIX(1.175875602) */ #define FIX_1_501321110 ((INT32) 12299) /* FIX(1.501321110) */ #define FIX_1_847759065 ((INT32) 15137) /* FIX(1.847759065) */ #define FIX_1_961570560 ((INT32) 16069) /* FIX(1.961570560) */ #define FIX_2_053119869 ((INT32) 16819) /* FIX(2.053119869) */ #define FIX_2_562915447 ((INT32) 20995) /* FIX(2.562915447) */ #define FIX_3_072711026 ((INT32) 25172) /* FIX(3.072711026) */ #else #define FIX_0_298631336 FIX(0.298631336) #define FIX_0_390180644 FIX(0.390180644) #define FIX_0_541196100 FIX(0.541196100) #define FIX_0_765366865 FIX(0.765366865) #define FIX_0_899976223 FIX(0.899976223) #define FIX_1_175875602 FIX(1.175875602) #define FIX_1_501321110 FIX(1.501321110) #define FIX_1_847759065 FIX(1.847759065) #define FIX_1_961570560 FIX(1.961570560) #define FIX_2_053119869 FIX(2.053119869) #define FIX_2_562915447 FIX(2.562915447) #define FIX_3_072711026 FIX(3.072711026) #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. * * Optimized algorithm with 12 multiplications in the 1-D kernel. * cK represents sqrt(2) * cos(K*pi/16). */ GLOBAL(void) jpeg_idct_islow (j_decompress_ptr cinfo, jpeg_component_info * compptr, JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col) { INT32 tmp0, tmp1, tmp2, tmp3; INT32 tmp10, tmp11, tmp12, tmp13; INT32 z1, z2, z3; JCOEFPTR inptr; ISLOW_MULT_TYPE * quantptr; int * wsptr; JSAMPROW o