| 1 | //===-- popcountsi2.c - Implement __popcountsi2 ---------------------------===// |
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| 2 | // |
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| 3 | // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
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| 4 | // See https://llvm.org/LICENSE.txt for license information. |
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| 5 | // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
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| 6 | // |
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| 7 | //===----------------------------------------------------------------------===// |
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| 8 | // |
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| 9 | // This file implements __popcountsi2 for the compiler_rt library. |
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| 10 | // |
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| 11 | //===----------------------------------------------------------------------===// |
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| 12 | |
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| 13 | #include "int_lib.h" |
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| 14 | |
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| 15 | // Returns: count of 1 bits |
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| 16 | |
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| 17 | COMPILER_RT_ABI int __popcountsi2(si_int a) { |
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| 18 | su_int x = (su_int)a; |
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| 19 | x = x - ((x >> 1) & 0x55555555); |
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| 20 | // Every 2 bits holds the sum of every pair of bits |
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| 21 | x = ((x >> 2) & 0x33333333) + (x & 0x33333333); |
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| 22 | // Every 4 bits holds the sum of every 4-set of bits (3 significant bits) |
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| 23 | x = (x + (x >> 4)) & 0x0F0F0F0F; |
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| 24 | // Every 8 bits holds the sum of every 8-set of bits (4 significant bits) |
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| 25 | x = (x + (x >> 16)); |
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| 26 | // The lower 16 bits hold two 8 bit sums (5 significant bits). |
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| 27 | // Upper 16 bits are garbage |
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| 28 | return (x + (x >> 8)) & 0x0000003F; // (6 significant bits) |
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| 29 | } |
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| 30 | |
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