| /* |
| * jfwddct.c |
| * |
| * Copyright (C) 1991, 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 the basic DCT (Discrete Cosine Transform) |
| * transformation subroutine. |
| * |
| * This implementation is based on Appendix A.2 of the book |
| * "Discrete Cosine Transform---Algorithms, Advantages, Applications" |
| * by K.R. Rao and P. Yip (Academic Press, Inc, London, 1990). |
| * It uses scaled fixed-point arithmetic instead of floating point. |
| */ |
| |
| #include "jinclude.h" |
| |
| |
| /* The poop on this scaling stuff is as follows: |
| * |
| * Most of the numbers (after multiplication by the constants) are |
| * (logically) shifted left by LG2_DCT_SCALE. This is undone by UNFIXH |
| * before assignment to the output array. Note that we want an additional |
| * division by 2 on the output (required by the equations). |
| * |
| * If right shifts are unsigned, then there is a potential problem. |
| * However, shifting right by 16 and then assigning to a short |
| * (assuming short = 16 bits) will keep the sign right!! |
| * |
| * For other shifts, |
| * |
| * ((x + (1 << 30)) >> shft) - (1 << (30 - shft)) |
| * |
| * gives a nice right shift with sign (assuming no overflow). However, all the |
| * scaling is such that this isn't a problem. (Is this true?) |
| */ |
| |
| |
| #define ONE 1L /* remove L if long > 32 bits */ |
| |
| #ifdef RIGHT_SHIFT_IS_UNSIGNED |
| #define LG2_DCT_SCALE 15 |
| #define RIGHT_SHIFT(_x,_shft) ((((_x) + (ONE << 30)) >> (_shft)) - (ONE << (30 - (_shft)))) |
| #else |
| #define LG2_DCT_SCALE 16 |
| #define RIGHT_SHIFT(_x,_shft) ((_x) >> (_shft)) |
| #endif |
| |
| #define DCT_SCALE (ONE << LG2_DCT_SCALE) |
| |
| #define LG2_OVERSCALE 2 |
| #define OVERSCALE (ONE << LG2_OVERSCALE) |
| |
| #define FIX(x) ((INT32) ((x) * DCT_SCALE + 0.5)) |
| #define FIXO(x) ((INT32) ((x) * DCT_SCALE / OVERSCALE + 0.5)) |
| #define UNFIX(x) RIGHT_SHIFT((x) + (ONE << (LG2_DCT_SCALE-1)), LG2_DCT_SCALE) |
| #define UNFIXH(x) RIGHT_SHIFT((x) + (ONE << LG2_DCT_SCALE), LG2_DCT_SCALE+1) |
| #define UNFIXO(x) RIGHT_SHIFT((x) + (ONE << (LG2_DCT_SCALE-1-LG2_OVERSCALE)), LG2_DCT_SCALE-LG2_OVERSCALE) |
| #define OVERSH(x) ((x) << LG2_OVERSCALE) |
| |
| #define SIN_1_4 FIX(0.7071067811856476) |
| #define COS_1_4 SIN_1_4 |
| |
| #define SIN_1_8 FIX(0.3826834323650898) |
| #define COS_1_8 FIX(0.9238795325112870) |
| #define SIN_3_8 COS_1_8 |
| #define COS_3_8 SIN_1_8 |
| |
| #define SIN_1_16 FIX(0.1950903220161282) |
| #define COS_1_16 FIX(0.9807852804032300) |
| #define SIN_7_16 COS_1_16 |
| #define COS_7_16 SIN_1_16 |
| |
| #define SIN_3_16 FIX(0.5555702330196022) |
| #define COS_3_16 FIX(0.8314696123025450) |
| #define SIN_5_16 COS_3_16 |
| #define COS_5_16 SIN_3_16 |
| |
| #define OSIN_1_4 FIXO(0.707106781185647) |
| #define OCOS_1_4 OSIN_1_4 |
| |
| #define OSIN_1_8 FIXO(0.3826834323650898) |
| #define OCOS_1_8 FIXO(0.9238795325112870) |
| #define OSIN_3_8 OCOS_1_8 |
| #define OCOS_3_8 OSIN_1_8 |
| |
| #define OSIN_1_16 FIXO(0.1950903220161282) |
| #define OCOS_1_16 FIXO(0.9807852804032300) |
| #define OSIN_7_16 OCOS_1_16 |
| #define OCOS_7_16 OSIN_1_16 |
| |
| #define OSIN_3_16 FIXO(0.5555702330196022) |
| #define OCOS_3_16 FIXO(0.8314696123025450) |
| #define OSIN_5_16 OCOS_3_16 |
| #define OCOS_5_16 OSIN_3_16 |
| |
| |
| INLINE |
| LOCAL void |
| fast_dct_8 (DCTELEM *in, int stride) |
| { |
| /* tmp1x are new values of tmpx -- flashy register colourers |
| * should be able to do this lot very well |
| */ |
| INT32 tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7; |
| INT32 tmp10, tmp11, tmp12, tmp13, tmp14, tmp15, tmp16, tmp17; |
| INT32 tmp25, tmp26; |
| INT32 in0, in1, in2, in3, in4, in5, in6, in7; |
| |
| in0 = in[ 0]; |
| in1 = in[stride ]; |
| in2 = in[stride*2]; |
| in3 = in[stride*3]; |
| in4 = in[stride*4]; |
| in5 = in[stride*5]; |
| in6 = in[stride*6]; |
| in7 = in[stride*7]; |
| |
| tmp0 = in7 + in0; |
| tmp1 = in6 + in1; |
| tmp2 = in5 + in2; |
| tmp3 = in4 + in3; |
| tmp4 = in3 - in4; |
| tmp5 = in2 - in5; |
| tmp6 = in1 - in6; |
| tmp7 = in0 - in7; |
| |
| tmp10 = tmp3 + tmp0 ; |
| tmp11 = tmp2 + tmp1 ; |
| tmp12 = tmp1 - tmp2 ; |
| tmp13 = tmp0 - tmp3 ; |
| |
| /* Now using tmp10, tmp11, tmp12, tmp13 */ |
| |
| in[ 0] = UNFIXH((tmp10 + tmp11) * SIN_1_4); |
| in[stride*4] = UNFIXH((tmp10 - tmp11) * COS_1_4); |
| |
| in[stride*2] = UNFIXH(tmp13*COS_1_8 + tmp12*SIN_1_8); |
| in[stride*6] = UNFIXH(tmp13*SIN_1_8 - tmp12*COS_1_8); |
| |
| tmp16 = UNFIXO((tmp6 + tmp5) * SIN_1_4); |
| tmp15 = UNFIXO((tmp6 - tmp5) * COS_1_4); |
| |
| /* Now using tmp10, tmp11, tmp13, tmp14, tmp15, tmp16 */ |
| |
| tmp14 = OVERSH(tmp4) + tmp15; |
| tmp25 = OVERSH(tmp4) - tmp15; |
| tmp26 = OVERSH(tmp7) - tmp16; |
| tmp17 = OVERSH(tmp7) + tmp16; |
| |
| /* These are now overscaled by OVERSCALE */ |
| |
| /* tmp10, tmp11, tmp12, tmp13, tmp14, tmp25, tmp26, tmp17 */ |
| |
| in[stride ] = UNFIXH(tmp17*OCOS_1_16 + tmp14*OSIN_1_16); |
| in[stride*7] = UNFIXH(tmp17*OCOS_7_16 - tmp14*OSIN_7_16); |
| in[stride*5] = UNFIXH(tmp26*OCOS_5_16 + tmp25*OSIN_5_16); |
| in[stride*3] = UNFIXH(tmp26*OCOS_3_16 - tmp25*OSIN_3_16); |
| } |
| |
| |
| /* |
| * Perform the forward DCT on one block of samples. |
| * |
| * Note that this code is specialized to the case DCTSIZE = 8. |
| */ |
| |
| GLOBAL void |
| j_fwd_dct (DCTBLOCK data) |
| { |
| int i; |
| |
| for (i = 0; i < DCTSIZE; i++) |
| fast_dct_8(data+i*DCTSIZE, 1); |
| |
| for (i = 0; i < DCTSIZE; i++) |
| fast_dct_8(data+i, DCTSIZE); |
| } |