}
}
+// AA&N (Arai, Agui and Nakajima) floating-point IDCT.
+// This IDCT is based on the same DCT that libjpeg uses -- in fact, exactly the
+// same figure from the same book ("JPEG: Still Image Data Compression Standard",
+// page 52, figure 4-8). However, it is coded from scratch, and uses the
+// transposition method for converting DCT -> IDCT suggested in the book.
+// (libjpeg seems to use some other method that yields similar, but not
+// the same, code.)
+
+// As this is generally meant as a reference and not useful code (we expect
+// a SIMD fixed-point algorithm to be used in most cases), it has not been
+// attempted significantly optimized. We assume the compiler will be smart
+// enough to do all the variable propagation for us anyway.
+
+// Scale factors; 1.0 / (sqrt(2.0) * cos(k * M_PI / 16.0)), except for the first which is 1.
+static const double scalefac[] = {
+ 1.0, 0.7209598220069479, 0.765366864730180, 0.8504300947672564,
+ 1.0, 1.2727585805728336, 1.847759065022573, 3.6245097854115502
+};
+
+// 1D 8-point DCT.
+static inline void idct1d_float(double y0, double y1, double y2, double y3, double y4, double y5, double y6, double y7, double *x)
+{
+ // constants
+ static const double a1 = 0.7071067811865474; // sqrt(2)
+ static const double a2 = 0.5411961001461971; // cos(3/8 pi) * sqrt(2)
+ static const double a3 = a1;
+ static const double a4 = 1.3065629648763766; // cos(pi/8) * sqrt(2)
+ static const double a5 = 0.5 * (a4 - a2);
+
+ // phase 1
+ const double p1_0 = y0 * scalefac[0];
+ const double p1_1 = y4 * scalefac[4];
+ const double p1_2 = y2 * scalefac[2];
+ const double p1_3 = y6 * scalefac[6];
+ const double p1_4 = y5 * scalefac[5];
+ const double p1_5 = y1 * scalefac[1];
+ const double p1_6 = y7 * scalefac[7];
+ const double p1_7 = y3 * scalefac[3];
+
+ // phase 2
+ const double p2_0 = p1_0;
+ const double p2_1 = p1_1;
+ const double p2_2 = p1_2;
+ const double p2_3 = p1_3;
+ const double p2_4 = p1_4 - p1_7;
+ const double p2_5 = p1_5 + p1_6;
+ const double p2_6 = p1_5 - p1_6;
+ const double p2_7 = p1_4 + p1_7;
+
+ // phase 3
+ const double p3_0 = p2_0;
+ const double p3_1 = p2_1;
+ const double p3_2 = p2_2 - p2_3;
+ const double p3_3 = p2_2 + p2_3;
+ const double p3_4 = p2_4;
+ const double p3_5 = p2_5 - p2_7;
+ const double p3_6 = p2_6;
+ const double p3_7 = p2_5 + p2_7;
+
+ // phase 4
+ const double p4_0 = p3_0;
+ const double p4_1 = p3_1;
+ const double p4_2 = a1 * p3_2;
+ const double p4_3 = p3_3;
+ const double p4_4 = p3_4 * -a2 + (p3_4 + p3_6) * -a5;
+ const double p4_5 = a3 * p3_5;
+ const double p4_6 = p3_6 * a4 + (p3_4 + p3_6) * -a5;
+ const double p4_7 = p3_7;
+
+ // phase 5
+ const double p5_0 = p4_0 + p4_1;
+ const double p5_1 = p4_0 - p4_1;
+ const double p5_2 = p4_2;
+ const double p5_3 = p4_2 + p4_3;
+ const double p5_4 = p4_4;
+ const double p5_5 = p4_5;
+ const double p5_6 = p4_6;
+ const double p5_7 = p4_7;
+
+ // phase 6
+ const double p6_0 = p5_0 + p5_3;
+ const double p6_1 = p5_1 + p5_2;
+ const double p6_2 = p5_1 - p5_2;
+ const double p6_3 = p5_0 - p5_3;
+ const double p6_4 = -p5_4;
+ const double p6_5 = p5_5 - p5_4;
+ const double p6_6 = p5_5 + p5_6;
+ const double p6_7 = p5_6 + p5_7;
+
+ // phase 7
+ x[0] = p6_0 + p6_7;
+ x[1] = p6_1 + p6_6;
+ x[2] = p6_2 + p6_5;
+ x[3] = p6_3 + p6_4;
+ x[4] = p6_3 - p6_4;
+ x[5] = p6_2 - p6_5;
+ x[6] = p6_1 - p6_6;
+ x[7] = p6_0 - p6_7;
+}
+
+void idct_float(const int16_t* input, const uint32_t* quant_table, uint8_t* output)
+{
+ double temp[DCTSIZE2];
+
+ // IDCT columns.
+ for (unsigned x = 0; x < DCTSIZE; ++x) {
+ idct1d_float(input[DCTSIZE * 0 + x] * (int32_t)quant_table[DCTSIZE * 0 + x],
+ input[DCTSIZE * 1 + x] * (int32_t)quant_table[DCTSIZE * 1 + x],
+ input[DCTSIZE * 2 + x] * (int32_t)quant_table[DCTSIZE * 2 + x],
+ input[DCTSIZE * 3 + x] * (int32_t)quant_table[DCTSIZE * 3 + x],
+ input[DCTSIZE * 4 + x] * (int32_t)quant_table[DCTSIZE * 4 + x],
+ input[DCTSIZE * 5 + x] * (int32_t)quant_table[DCTSIZE * 5 + x],
+ input[DCTSIZE * 6 + x] * (int32_t)quant_table[DCTSIZE * 6 + x],
+ input[DCTSIZE * 7 + x] * (int32_t)quant_table[DCTSIZE * 7 + x],
+ temp + x * DCTSIZE);
+ }
+
+ // IDCT rows.
+ for (unsigned y = 0; y < DCTSIZE; ++y) {
+ double temp2[DCTSIZE];
+ idct1d_float(temp[DCTSIZE * 0 + y],
+ temp[DCTSIZE * 1 + y],
+ temp[DCTSIZE * 2 + y],
+ temp[DCTSIZE * 3 + y],
+ temp[DCTSIZE * 4 + y],
+ temp[DCTSIZE * 5 + y],
+ temp[DCTSIZE * 6 + y],
+ temp[DCTSIZE * 7 + y],
+ temp2);
+ for (unsigned x = 0; x < DCTSIZE; ++x) {
+ double val = (1.0/8.0) * temp2[x];
+ if (val < 0.0) {
+ output[y * DCTSIZE + x] = 0;
+ } else if (val >= 255.0) {
+ output[y * DCTSIZE + x] = 255;
+ } else {
+ output[y * DCTSIZE + x] = (uint8_t)(val + 0.5);
+ }
+ }
+ }
+}
projects / fjl / blobdiff