Abastro/mathematical-algorithms-cpp
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Can subspan this

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Abastro 2025-03-25 22:23:01 +09:00
parent 6f30ac9341
commit 7123942c9d
1 changed files with 9 additions and 7 deletions
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16
src/karatsuba.cpp
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@ -139,21 +139,23 @@ void poly_mult_Karatsuba_step(const size_t deg_bnd, span<R> &a, span<R> &b,
auto b0 = b.subspan(0, next_bnd);
auto b1 = b.subspan(next_bnd, next_bnd);
auto store = vector<R>(next_bnd * 4);
auto a01 = span(store.begin() + 0, next_bnd);
auto b01 = span(store.begin() + next_bnd, next_bnd);
auto a01 = buffer.subspan(0, next_bnd);
auto b01 = buffer.subspan(next_bnd, next_bnd);
auto prod0 = result.subspan(0, deg_bnd);
auto prod1 = result.subspan(deg_bnd, deg_bnd);
auto prod_add = span(store.begin() + 2 * next_bnd, deg_bnd);
auto prod_add_vec = vector<R>(deg_bnd);
auto prod_add = span(prod_add_vec);
auto next_buffer = buffer.subspan(next_bnd * 4, next_bnd * 4);
// correctly put into prod0 and prod1 position
poly_mult_Karatsuba_step(next_bnd, a0, b0, prod0, buffer);
poly_mult_Karatsuba_step(next_bnd, a1, b1, prod1, buffer);
poly_mult_Karatsuba_step(next_bnd, a0, b0, prod0, next_buffer);
poly_mult_Karatsuba_step(next_bnd, a1, b1, prod1, next_buffer);
add_inplace(a0, a1, a01);
add_inplace(b0, b1, b01);
poly_mult_Karatsuba_step(next_bnd, a01, b01, prod_add, buffer);
poly_mult_Karatsuba_step(next_bnd, a01, b01, prod_add, next_buffer);
// adjust prod_add
sub_inplace(prod_add, prod0, prod_add);