llvm-project

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//===-- int_mulv_impl.inc - Implement __mulv[sdt]i3 ---------------*- C -*-===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// Helper used by __mulvsi3, __mulvdi3 and __mulvti3.
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//
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//===----------------------------------------------------------------------===//
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#include "int_lib.h"
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// Returns: a * b
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// Effects: aborts if a * b overflows
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static __inline fixint_t __mulvXi3(fixint_t a, fixint_t b) {
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  const int N = (int)(sizeof(fixint_t) * CHAR_BIT);
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  const fixint_t MIN = (fixint_t)((fixuint_t)1 << (N - 1));
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  const fixint_t MAX = ~MIN;
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  if (a == MIN) {
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    if (b == 0 || b == 1)
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      return a * b;
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    compilerrt_abort();
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  }
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  if (b == MIN) {
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    if (a == 0 || a == 1)
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      return a * b;
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    compilerrt_abort();
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  }
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  fixint_t sa = a >> (N - 1);
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  fixint_t abs_a = (a ^ sa) - sa;
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  fixint_t sb = b >> (N - 1);
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  fixint_t abs_b = (b ^ sb) - sb;
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  if (abs_a < 2 || abs_b < 2)
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    return a * b;
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  if (sa == sb) {
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    if (abs_a > MAX / abs_b)
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      compilerrt_abort();
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  } else {
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    if (abs_a > MIN / -abs_b)
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      compilerrt_abort();
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  }
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  return a * b;
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}
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