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A bit more minor optimization

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This commit is contained in:
vub 2017-04-23 20:15:16 -04:00
parent d800eafa2a
commit 8672819248
1 changed files with 7 additions and 6 deletions
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13
erasure_code/ec65536/poly_utils.cpp
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@ -159,10 +159,10 @@ vector<int> subroot_linear_combination(vector<int> xs, vector<int> factors) {
} }
vector<int> derivative(vector<int> p) { vector<int> derivative_and_square_base(vector<int> p) {
vector<int> o(p.size() - 1); vector<int> o((p.size() - 1) / 2);
for (int i = 0; i < o.size(); i+= 2) { for (int i = 0; i < o.size(); i+= 1) {
o[i] = p[i + 1]; o[i] = p[i * 2 + 1];
} }
return o; return o;
} }
@ -181,10 +181,11 @@ vector<int> poly_to_logs(vector<int> p) {
vector<int> lagrange_interp(vector<int> ys, vector<int> xs) { vector<int> lagrange_interp(vector<int> ys, vector<int> xs) {
int xs_size = xs.size(); int xs_size = xs.size();
vector<int> root = mk_root(xs); vector<int> root = mk_root(xs);
vector<int> log_rootprime = poly_to_logs(derivative(root)); vector<int> log_rootprime = poly_to_logs(derivative_and_square_base(root));
vector<int> factors(xs_size); vector<int> factors(xs_size);
for (int i = 0; i < xs_size; i++) { for (int i = 0; i < xs_size; i++) {
int denom = eval_log_poly_at(log_rootprime, xs[i]); int x_square = xs[i] ? gexptable[glogtable[xs[i]] * 2] : 0;
int denom = eval_log_poly_at(log_rootprime, x_square);
if (ys[i]) if (ys[i])
factors[i] = gexptable[glogtable[ys[i]] + 65535 - glogtable[denom]]; factors[i] = gexptable[glogtable[ys[i]] + 65535 - glogtable[denom]];
} }