chromium/v8/src/bigint/mul-schoolbook.cc

// Copyright 2021 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "src/bigint/bigint-internal.h"
#include "src/bigint/digit-arithmetic.h"
#include "src/bigint/vector-arithmetic.h"

namespace v8 {
namespace bigint {

// Z := X * y, where y is a single digit.
void ProcessorImpl::MultiplySingle(RWDigits Z, Digits X, digit_t y) { … }

#define BODY …

// Z := X * Y.
// O(n²) "schoolbook" multiplication algorithm. Optimized to minimize
// bounds and overflow checks: rather than looping over X for every digit
// of Y (or vice versa), we loop over Z. The {BODY} macro above is what
// computes one of Z's digits as a sum of the products of relevant digits
// of X and Y. This yields a nearly 2x improvement compared to more obvious
// implementations.
// This method is *highly* performance sensitive even for the advanced
// algorithms, which use this as the base case of their recursive calls.
void ProcessorImpl::MultiplySchoolbook(RWDigits Z, Digits X, Digits Y) { … }

#undef BODY

}  // namespace bigint
}  // namespace v8