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/* ===-- popcountsi2.c - Implement __popcountsi2 ---------------------------=== |
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* |
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* The LLVM Compiler Infrastructure |
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* |
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* This file is dual licensed under the MIT and the University of Illinois Open |
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* Source Licenses. See LICENSE.TXT for details. |
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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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*/ |
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#include "int_lib.h" |
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/* Returns: count of 1 bits */ |
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COMPILER_RT_ABI si_int |
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__popcountsi2(si_int a) |
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{ |
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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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} |