llvm-project

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//===-- popcountdi2.c - Implement __popcountdi2 ---------------------------===//
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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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// This file implements __popcountdi2 for the compiler_rt library.
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//
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//===----------------------------------------------------------------------===//
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#include "int_lib.h"
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// Returns: count of 1 bits
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COMPILER_RT_ABI int __popcountdi2(di_int a) {
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  du_int x2 = (du_int)a;
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  x2 = x2 - ((x2 >> 1) & 0x5555555555555555uLL);
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  // Every 2 bits holds the sum of every pair of bits (32)
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  x2 = ((x2 >> 2) & 0x3333333333333333uLL) + (x2 & 0x3333333333333333uLL);
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  // Every 4 bits holds the sum of every 4-set of bits (3 significant bits) (16)
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  x2 = (x2 + (x2 >> 4)) & 0x0F0F0F0F0F0F0F0FuLL;
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  // Every 8 bits holds the sum of every 8-set of bits (4 significant bits) (8)
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  su_int x = (su_int)(x2 + (x2 >> 32));
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  // The lower 32 bits hold four 16 bit sums (5 significant bits).
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  //   Upper 32 bits are garbage
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  x = x + (x >> 16);
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  // The lower 16 bits hold two 32 bit sums (6 significant bits).
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  //   Upper 16 bits are garbage
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  return (x + (x >> 8)) & 0x0000007F; // (7 significant bits)
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}
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