7 #define LANCZOS_RADIUS 30
13 return 1.0f - fabs(x);
20 double weight(double x)
22 if (fabs(x) > LANCZOS_RADIUS) {
25 return sinc(M_PI * x) * sinc(M_PI * x / LANCZOS_RADIUS);
28 double weight(double x)
33 return 1.0f - fabs(x);
37 double interpolate(const short *in, double i)
39 int lower = std::max(int(ceil(i - LANCZOS_RADIUS)), 0);
40 int upper = std::min(int(floor(i + LANCZOS_RADIUS)), LEN - 1);
43 for (int x = lower; x <= upper; ++x) {
44 sum += in[x] * weight(i - x);
52 double find_zerocrossing(int x)
61 assert(in[x + 1] > 0);
66 while (upper - lower > 1e-6) {
67 double mid = 0.5f * (upper + lower);
68 if (interpolate(in, mid) > 0) {
75 return 0.5f * (upper + lower);
78 int main(int argc, char **argv)
80 fread(in, LEN*2, 1, stdin);
83 for (int i = 0; i < LEN; ++i) {
84 in[i] += rand() % 10000;
89 for (int i = 0; i < LEN; ++i) {
90 printf("%d\n", in[i]);
94 double last_upflank = -1;
95 for (int i = 0; i < LEN; ++i) {
96 int bit = (in[i] > 0) ? 1 : 0;
97 if (bit == 1 && last_bit == 0) {
99 double t = find_zerocrossing(i - 1) * (123156.0/44100.0);
100 if (last_upflank > 0) {
101 // fprintf(stderr, "length: %f (0x%x)\n", t - last_upflank, lrintf(t - last_upflank));
102 int len = lrintf(t - last_upflank);
103 printf("0x%x\n", len);