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#include "Halide.h"
using namespace Halide;
// Order a pair of Exprs, treating undefined Exprs as infinity
void sort2(Expr &a, Expr &b) {
if (!a.defined()) {
std::swap(a, b);
} else if (!b.defined()) {
return;
} else {
Expr tmp = min(a, b);
b = max(a, b);
a = tmp;
}
}
// Bitonic sort a vector of Exprs
std::vector<Expr> bitonic_sort_inner(std::vector<Expr> v, bool flipped) {
size_t size = v.size();
size_t half_size = size / 2;
if (!half_size) return v;
std::vector<Expr>::iterator middle = v.begin() + half_size;
std::vector<Expr> a, b;
a.insert(a.begin(), v.begin(), middle);
b.insert(b.begin(), middle, v.end());
// Sort each half
a = bitonic_sort_inner(a, true);
b = bitonic_sort_inner(b, false);
assert(a.size() == half_size);
assert(b.size() == half_size);
// Concat the results
a.insert(a.end(), b.begin(), b.end());
// Bitonic merge
for (size_t stride = half_size; stride > 0; stride /= 2) {
for (size_t i = 0; i < size; i++) {
if (i % (2 * stride) < stride) {
if (!flipped) {
sort2(a[i], a[i + stride]);
} else {
sort2(a[i + stride], a[i]);
}
}
}
}
return a;
}
std::vector<Expr> bitonic_sort(std::vector<Expr> v) {
// Bulk up the vector to a power of two using infinities
while (v.size() & (v.size() - 1)) {
v.push_back(Expr());
}
v = bitonic_sort_inner(v, false);
while (!v.back().defined()) {
v.pop_back();
}
return v;
}
Expr median(std::vector<Expr> v) {
v = bitonic_sort(v);
return v[v.size() / 2];
}
int main(int argc, char **argv) {
Func f;
Var x;
f(x) = sin(x);
f.compute_root();
const int N = 9;
std::vector<Expr> exprs;
for (int i = 0; i < N; i++) {
exprs.push_back(f(i));
}
exprs = bitonic_sort(exprs);
std::cout << exprs.size() << "\n";
// Use update definitions to write them to another Func in sorted
// order for inspection. Note that doing this doesn't explicitly
// share work between each element - it'll generate the huge
// min/max expression to extract each sorted element. llvm should
// lift out common subexpressions though.
Func g;
g(x) = undef<float>();
for (int i = 0; i < N; i++) {
g(i) = exprs[i];
}
Buffer<float> result = g.realize({N});
for (int i = 0; i < N; i++) {
printf("%f ", result(i));
}
printf("\n");
for (int i = 0; i < N - 1; i++) {
if (result(i) >= result(i + 1)) {
printf("Results were not in order\n");
return 1;
}
}
printf("Success!\n");
return 0;
}
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