forked from OSchip/llvm-project
30 lines
1.1 KiB
C
30 lines
1.1 KiB
C
//===-- popcountsi2.c - Implement __popcountsi2 ---------------------------===//
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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 __popcountsi2 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 __popcountsi2(si_int a) {
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su_int x = (su_int)a;
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x = x - ((x >> 1) & 0x55555555);
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// Every 2 bits holds the sum of every pair of bits
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x = ((x >> 2) & 0x33333333) + (x & 0x33333333);
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// Every 4 bits holds the sum of every 4-set of bits (3 significant bits)
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x = (x + (x >> 4)) & 0x0F0F0F0F;
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// Every 8 bits holds the sum of every 8-set of bits (4 significant bits)
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x = (x + (x >> 16));
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// The lower 16 bits hold two 8 bit sums (5 significant bits).
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// Upper 16 bits are garbage
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return (x + (x >> 8)) & 0x0000003F; // (6 significant bits)
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}
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