third_party/llvm-project/compiler-rt/lib/builtins/multi3.c

//===-- multi3.c - Implement __multi3 -------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file implements __multi3 for the compiler_rt library.
//
//===----------------------------------------------------------------------===//

#include "int_lib.h"

#ifdef CRT_HAS_128BIT

// Returns: a * b

static ti_int __mulddi3(du_int a, du_int b) {
  twords r;
  const int bits_in_dword_2 = (int)(sizeof(di_int) * CHAR_BIT) / 2;
  const du_int lower_mask = (du_int)~0 >> bits_in_dword_2;
  r.s.low = (a & lower_mask) * (b & lower_mask);
  du_int t = r.s.low >> bits_in_dword_2;
  r.s.low &= lower_mask;
  t += (a >> bits_in_dword_2) * (b & lower_mask);
  r.s.low += (t & lower_mask) << bits_in_dword_2;
  r.s.high = t >> bits_in_dword_2;
  t = r.s.low >> bits_in_dword_2;
  r.s.low &= lower_mask;
  t += (b >> bits_in_dword_2) * (a & lower_mask);
  r.s.low += (t & lower_mask) << bits_in_dword_2;
  r.s.high += t >> bits_in_dword_2;
  r.s.high += (a >> bits_in_dword_2) * (b >> bits_in_dword_2);
  return r.all;
}

// Returns: a * b

COMPILER_RT_ABI ti_int __multi3(ti_int a, ti_int b) {
  twords x;
  x.all = a;
  twords y;
  y.all = b;
  twords r;
  r.all = __mulddi3(x.s.low, y.s.low);
  r.s.high += x.s.high * y.s.low + x.s.low * y.s.high;
  return r.all;
}

#endif // CRT_HAS_128BIT