40 lines
1.5 KiB
C
40 lines
1.5 KiB
C
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/* clang-format off */
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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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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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__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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}
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