llvm-project

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//===-- popcountti2.c - Implement __popcountti2
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//----------------------------===//
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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 __popcountti2 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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#ifdef CRT_HAS_128BIT
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// Returns: count of 1 bits
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COMPILER_RT_ABI int __popcountti2(ti_int a) {
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  tu_int x3 = (tu_int)a;
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  x3 = x3 - ((x3 >> 1) &
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             (((tu_int)0x5555555555555555uLL << 64) | 0x5555555555555555uLL));
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  // Every 2 bits holds the sum of every pair of bits (64)
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  x3 = ((x3 >> 2) &
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        (((tu_int)0x3333333333333333uLL << 64) | 0x3333333333333333uLL)) +
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       (x3 & (((tu_int)0x3333333333333333uLL << 64) | 0x3333333333333333uLL));
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  // Every 4 bits holds the sum of every 4-set of bits (3 significant bits) (32)
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  x3 = (x3 + (x3 >> 4)) &
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       (((tu_int)0x0F0F0F0F0F0F0F0FuLL << 64) | 0x0F0F0F0F0F0F0F0FuLL);
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  // Every 8 bits holds the sum of every 8-set of bits (4 significant bits) (16)
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  du_int x2 = (du_int)(x3 + (x3 >> 64));
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  // Every 8 bits holds the sum of every 8-set of bits (5 significant bits) (8)
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  su_int x = (su_int)(x2 + (x2 >> 32));
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  // Every 8 bits holds the sum of every 8-set of bits (6 significant bits) (4)
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  x = x + (x >> 16);
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  // Every 8 bits holds the sum of every 8-set of bits (7 significant bits) (2)
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  //
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  // Upper 16 bits are garbage
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  return (x + (x >> 8)) & 0xFF; // (8 significant bits)
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}
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#endif // CRT_HAS_128BIT
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