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/* ===-- popcountdi2.c - Implement __popcountdi2 ----------------------------=== |
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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 __popcountdi2 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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__popcountdi2(di_int a) |
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{ |
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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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} |