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61 lines
1.2 KiB
C++
61 lines
1.2 KiB
C++
//
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// ffs.hpp
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// OpenVPN
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//
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// Copyright (c) 2012 OpenVPN Technologies, Inc. All rights reserved.
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//
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#ifndef OPENVPN_COMMON_FFS_H
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#define OPENVPN_COMMON_FFS_H
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#include <strings.h> // for ffs (and fls on BSD)
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#include <openvpn/common/platform.hpp>
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namespace openvpn {
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// find the zero-based position of the first 1 bit in a word
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// (scanning from least significant bit to most significant)
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inline const int find_first_set(unsigned int v)
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{
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return ffs(v) - 1;
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}
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// find the one-based position of the last 1 bit in a word
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// (scanning from most significant bit to least significant)
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inline const int find_last_set(unsigned int v)
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{
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#if defined(OPENVPN_PLATFORM_TYPE_APPLE)
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return fls(v); // apparently only BSD-based platforms have this
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#else
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int r = 32;
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if (!v)
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return 0;
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if (!(v & 0xffff0000u)) {
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v <<= 16;
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r -= 16;
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}
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if (!(v & 0xff000000u)) {
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v <<= 8;
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r -= 8;
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}
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if (!(v & 0xf0000000u)) {
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v <<= 4;
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r -= 4;
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}
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if (!(v & 0xc0000000u)) {
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v <<= 2;
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r -= 2;
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}
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if (!(v & 0x80000000u)) {
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v <<= 1;
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r -= 1;
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}
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return r;
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#endif
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}
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} // namespace openvpn
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#endif // OPENVPN_COMMON_FFS_H
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