1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
|
#include "Halide.h"
using namespace Halide;
int main(int argc, char **argv) {
// Halide only provides 32-bit noise functions, which are overkill for
// generating low bit-depth noise (e.g. for dithering). This test shows how
// to generate 8-bit noise by slicing out bytes from 32-bit noise.
Var x;
Func noise;
noise(x) = random_uint();
Func noise8;
noise8(x) = extract_bits<uint8_t>(noise(x / 4), 8 * (x % 4));
Func in16;
in16(x) = cast<uint16_t>(x);
Func dithered;
dithered(x) = cast<uint8_t>((in16(x) + noise8(x)) >> 8);
in16.compute_root();
dithered.compute_root().vectorize(x, 16, TailStrategy::RoundUp);
noise8.compute_at(dithered, x).vectorize(x);
// To keep things aligned:
dithered.output_buffer().dim(0).set_min(0);
Buffer<uint8_t> out = dithered.realize({1 << 15});
uint32_t sum = 0, correct_sum = 0;
for (int i = 0; i < out.width(); i++) {
sum += out(i);
correct_sum += i;
}
correct_sum = (correct_sum + 128) >> 8;
if (std::abs((double)sum - correct_sum) / correct_sum > 1e-4) {
printf("Suspiciously large relative difference between the sum of the dithered values and the full-precision sum: %d vs %d\n", sum, correct_sum);
return 1;
}
printf("Success!\n");
return 0;
}
|
