/* DCT1D_01.c version mar jan 1 08:45:57 GMT 2002 whygee@f-cpu.org 1* 8-bin DCT for a "baseline" JPG compressor. originally cut and pasted from : sbcci_DCT2D.pdf "Pipelined Fast 2-D DCT Architecture for JPEG Image Compression" Luciano Volcan Agostini Ivan Saraiva Silva Sergio Bampi Table 2 : Bit width differences between the two 1-D DCT architectures Pipeline First 1-D DCT Second 1-D DCT Stage bit width bit width 1 9 13 2 10 14 3 11 15 4 11 15 5 12 15 6 12 15 => the data are in 1Q15 format and left-aligned at the beginning. m1 = cos(4pi/16) m2 = cos(6pi/16) m3 = cos(2pi/16) - cos(6pi/16) m4 = cos(2pi/16)+ cos(6pi/16) Optimisation : part 1 = variable name inference A lot of work was already done so it is easy to short-circuit temporary variables. Each level (a to S) is an individual layer so the verification range is reduced. b2 bug corrected on Tue Dec 16 06:37:45 CET 2003 */ sample b0, b1, b2, b3, b4, b5, b6, b7, c0, c1, c2, c3, c4, c5, c6, d0, d1, d3, d4, e2, e3, e4, e6, e7, f2, f3, f4, f5, f6, f7; /* Step 1 */ b0 = a0 + a7; b1 = a1 + a6; b2 = a3 - a4; /* corrected */ b3 = a1 - a6; b4 = a2 + a5; b5 = a3 + a4; b6 = a2 - a5; b7 = a0 - a7; /* Step 2 */ c0 = b0 + b5; c1 = b1 - b4; c2 = b2 + b6; c3 = b1 + b4; c4 = b0 - b5; c5 = b3 + b7; c6 = b3 + b6; /*c7 = b7;*/ /* Step 3 */ d0 = c0 + c3; d1 = c0 - c3; /* d2 = c2; */ d3 = c1 + c4; d4 = c2 - c5; /*d5 = c4;*/ /*d6 = c5;*/ /*d7 = c6;*/ /*d8 = c7 = b7;*/ /* Step 4 */ /*e0 = d0;*/ /*e1 = d1;*/ e2 = m3 * /*d2 =*/ c2; e3 = m1 * /*d7 =*/ c6; e4 = m4 * /*d6 =*/ c5; /* e5 = d5 =c4; */ e6 = m1 * d3; e7 = m2 * d4; /*e8 = d8;*/ /* Step 5 */ /*f0 = e0 = d0;*/ /*f1 = e1 = d1;*/ f2 = c4 /*e5*/ + e6; f3 = c4 /*e5*/ - e6; f4 = e3 + /*e8 =*/ b7; f5 = /*e8 =*/ b7 - e3; f6 = e2 + e7; f7 = e4 + e7; /* Step 6 */ S0 = d0 /* = f0*/; S1 = f4 + f7; S2 = f2; S3 = f5 - f6; S4 = d1 /* = f1 */; S5 = f5 + f6; S6 = f3; S7 = f4 - f7;