37 lines
1.3 KiB
C
37 lines
1.3 KiB
C
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/* clang-format off */
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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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STATIC_YOINK("huge_compiler_rt_license");
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#include "third_party/compiler_rt/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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}
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