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/*
* Copyright 2017 Facebook, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include <folly/Bits.h>
#include <folly/CpuId.h>
#include <folly/Portability.h>
// None of this is necessary if we're compiling for a target that supports
// popcnt, which includes MSVC
#if !defined(__POPCNT__) && !defined(_MSC_VER)
namespace {
int popcount_builtin(unsigned int x) {
return __builtin_popcount(x);
}
int popcountll_builtin(unsigned long long x) {
return __builtin_popcountll(x);
}
#if FOLLY_HAVE_IFUNC && !defined(FOLLY_SANITIZE_ADDRESS)
// Strictly speaking, these versions of popcount are usable without ifunc
// support. However, we would have to check, via CpuId, if the processor
// implements the popcnt instruction first, which is what we use ifunc for.
int popcount_inst(unsigned int x) {
int n;
asm ("popcntl %1, %0" : "=r" (n) : "r" (x));
return n;
}
int popcountll_inst(unsigned long long x) {
unsigned long long n;
asm ("popcntq %1, %0" : "=r" (n) : "r" (x));
return n;
}
typedef decltype(popcount_builtin) Type_popcount;
typedef decltype(popcountll_builtin) Type_popcountll;
// This function is called on startup to resolve folly::detail::popcount
extern "C" Type_popcount* folly_popcount_ifunc() {
return folly::CpuId().popcnt() ? popcount_inst : popcount_builtin;
}
// This function is called on startup to resolve folly::detail::popcountll
extern "C" Type_popcountll* folly_popcountll_ifunc() {
return folly::CpuId().popcnt() ? popcountll_inst : popcountll_builtin;
}
#endif // FOLLY_HAVE_IFUNC && !defined(FOLLY_SANITIZE_ADDRESS)
} // namespace
namespace folly {
namespace detail {
// Call folly_popcount_ifunc on startup to resolve to either popcount_inst
// or popcount_builtin
int popcount(unsigned int x)
#if FOLLY_HAVE_IFUNC && !defined(FOLLY_SANITIZE_ADDRESS)
__attribute__((__ifunc__("folly_popcount_ifunc")));
#else
{ return popcount_builtin(x); }
#endif
// Call folly_popcount_ifunc on startup to resolve to either popcountll_inst
// or popcountll_builtin
int popcountll(unsigned long long x)
#if FOLLY_HAVE_IFUNC && !defined(FOLLY_SANITIZE_ADDRESS)
__attribute__((__ifunc__("folly_popcountll_ifunc")));
#else
{ return popcountll_builtin(x); }
#endif
} // namespace detail
} // namespace folly
#endif /* !__POPCNT__ */