| 1 | //===-- popcountdi2.c - Implement __popcountdi2 ---------------------------===// |
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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 __popcountdi2 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 __popcountdi2(di_int a) { |
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| 18 | du_int x2 = (du_int)a; |
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| 19 | x2 = x2 - ((x2 >> 1) & 0x5555555555555555uLL); |
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| 20 | // Every 2 bits holds the sum of every pair of bits (32) |
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| 21 | x2 = ((x2 >> 2) & 0x3333333333333333uLL) + (x2 & 0x3333333333333333uLL); |
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| 22 | // Every 4 bits holds the sum of every 4-set of bits (3 significant bits) (16) |
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| 23 | x2 = (x2 + (x2 >> 4)) & 0x0F0F0F0F0F0F0F0FuLL; |
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| 24 | // Every 8 bits holds the sum of every 8-set of bits (4 significant bits) (8) |
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| 25 | su_int x = (su_int)(x2 + (x2 >> 32)); |
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| 26 | // The lower 32 bits hold four 16 bit sums (5 significant bits). |
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| 27 | // Upper 32 bits are garbage |
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| 28 | x = x + (x >> 16); |
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| 29 | // The lower 16 bits hold two 32 bit sums (6 significant bits). |
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| 30 | // Upper 16 bits are garbage |
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| 31 | return (x + (x >> 8)) & 0x0000007F; // (7 significant bits) |
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| 32 | } |
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| 33 | |
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