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94 lines
2.7 KiB
C++
94 lines
2.7 KiB
C++
/*
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* Copyright 2016 Facebook, Inc.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#include <folly/Bits.h>
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#include <folly/CpuId.h>
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#include <folly/Portability.h>
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// None of this is necessary if we're compiling for a target that supports
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// popcnt, which includes MSVC
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#if !defined(__POPCNT__) && !defined(_MSC_VER)
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namespace {
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int popcount_builtin(unsigned int x) {
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return __builtin_popcount(x);
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}
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int popcountll_builtin(unsigned long long x) {
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return __builtin_popcountll(x);
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}
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#if FOLLY_HAVE_IFUNC && !defined(FOLLY_SANITIZE_ADDRESS)
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// Strictly speaking, these versions of popcount are usable without ifunc
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// support. However, we would have to check, via CpuId, if the processor
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// implements the popcnt instruction first, which is what we use ifunc for.
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int popcount_inst(unsigned int x) {
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int n;
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asm ("popcntl %1, %0" : "=r" (n) : "r" (x));
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return n;
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}
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int popcountll_inst(unsigned long long x) {
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unsigned long long n;
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asm ("popcntq %1, %0" : "=r" (n) : "r" (x));
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return n;
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}
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typedef decltype(popcount_builtin) Type_popcount;
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typedef decltype(popcountll_builtin) Type_popcountll;
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// This function is called on startup to resolve folly::detail::popcount
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extern "C" Type_popcount* folly_popcount_ifunc() {
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return folly::CpuId().popcnt() ? popcount_inst : popcount_builtin;
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}
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// This function is called on startup to resolve folly::detail::popcountll
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extern "C" Type_popcountll* folly_popcountll_ifunc() {
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return folly::CpuId().popcnt() ? popcountll_inst : popcountll_builtin;
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}
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#endif // FOLLY_HAVE_IFUNC && !defined(FOLLY_SANITIZE_ADDRESS)
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} // namespace
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namespace folly {
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namespace detail {
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// Call folly_popcount_ifunc on startup to resolve to either popcount_inst
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// or popcount_builtin
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int popcount(unsigned int x)
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#if FOLLY_HAVE_IFUNC && !defined(FOLLY_SANITIZE_ADDRESS)
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__attribute__((__ifunc__("folly_popcount_ifunc")));
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#else
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{ return popcount_builtin(x); }
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#endif
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// Call folly_popcount_ifunc on startup to resolve to either popcountll_inst
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// or popcountll_builtin
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int popcountll(unsigned long long x)
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#if FOLLY_HAVE_IFUNC && !defined(FOLLY_SANITIZE_ADDRESS)
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__attribute__((__ifunc__("folly_popcountll_ifunc")));
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#else
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{ return popcountll_builtin(x); }
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#endif
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} // namespace detail
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} // namespace folly
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#endif /* !__POPCNT__ */
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