X-Git-Url: https://git.sesse.net/?p=fjl;a=blobdiff_plain;f=idct.c;fp=idct.c;h=54a9dc9a9ecaa6a0e3bea13b33cc626c42587309;hp=0000000000000000000000000000000000000000;hb=039d3c953460ec41fa8b1f9d26e9cf62a344c8ef;hpb=823f82d1e860f1260c483ef544c4e9532132c7e8

diff --git a/idct.c b/idct.c
new file mode 100644
index 0000000..54a9dc9
--- /dev/null
+++ b/idct.c
@@ -0,0 +1,39 @@
+#include <math.h>
+
+#include "idct.h"
+
+void idct_reference(const int16_t* input, const uint32_t* quant_table, uint8_t* output)
+{
+	double temp[DCTSIZE2];
+
+	for (unsigned y = 0; y < 8; ++y) {
+		for (unsigned x = 0; x < 8; ++x) {
+			double acc = 0.0;
+			for (unsigned u = 0; u < 8; ++u) {
+				for (unsigned v = 0; v < 8; ++v) {
+					double c_u = (u == 0) ? 1/sqrt(2.0) : 1.0;
+					double c_v = (v == 0) ? 1/sqrt(2.0) : 1.0;
+					acc += c_u * c_v
+						* input[u * DCTSIZE + v] * quant_table[u * DCTSIZE + v]
+						* cos((2 * x + 1) * v * M_PI / 16.0)
+						* cos((2 * y + 1) * u * M_PI / 16.0);
+				}
+			}
+			temp[y * DCTSIZE + x] = 0.25 * acc;
+		}
+	}
+
+	for (unsigned y = 0; y < 8; ++y) {
+		for (unsigned x = 0; x < 8; ++x) {
+			double val = temp[y * DCTSIZE + 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);
+			}
+		}
+	}
+}
+