2 * Copyright 2016 Facebook, Inc.
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
8 * http://www.apache.org/licenses/LICENSE-2.0
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
17 #include <folly/Bits.h>
19 #include <folly/CpuId.h>
20 #include <folly/Portability.h>
22 // None of this is necessary if we're compiling for a target that supports
23 // popcnt, which includes MSVC
24 #if !defined(__POPCNT__) && !defined(_MSC_VER)
27 int popcount_builtin(unsigned int x) {
28 return __builtin_popcount(x);
31 int popcountll_builtin(unsigned long long x) {
32 return __builtin_popcountll(x);
35 #if FOLLY_HAVE_IFUNC && !defined(FOLLY_SANITIZE_ADDRESS)
37 // Strictly speaking, these versions of popcount are usable without ifunc
38 // support. However, we would have to check, via CpuId, if the processor
39 // implements the popcnt instruction first, which is what we use ifunc for.
40 int popcount_inst(unsigned int x) {
42 asm ("popcntl %1, %0" : "=r" (n) : "r" (x));
46 int popcountll_inst(unsigned long long x) {
48 asm ("popcntq %1, %0" : "=r" (n) : "r" (x));
52 typedef decltype(popcount_builtin) Type_popcount;
53 typedef decltype(popcountll_builtin) Type_popcountll;
55 // This function is called on startup to resolve folly::detail::popcount
56 extern "C" Type_popcount* folly_popcount_ifunc() {
57 return folly::CpuId().popcnt() ? popcount_inst : popcount_builtin;
60 // This function is called on startup to resolve folly::detail::popcountll
61 extern "C" Type_popcountll* folly_popcountll_ifunc() {
62 return folly::CpuId().popcnt() ? popcountll_inst : popcountll_builtin;
65 #endif // FOLLY_HAVE_IFUNC && !defined(FOLLY_SANITIZE_ADDRESS)
72 // Call folly_popcount_ifunc on startup to resolve to either popcount_inst
73 // or popcount_builtin
74 int popcount(unsigned int x)
75 #if FOLLY_HAVE_IFUNC && !defined(FOLLY_SANITIZE_ADDRESS)
76 __attribute__((__ifunc__("folly_popcount_ifunc")));
78 { return popcount_builtin(x); }
81 // Call folly_popcount_ifunc on startup to resolve to either popcountll_inst
82 // or popcountll_builtin
83 int popcountll(unsigned long long x)
84 #if FOLLY_HAVE_IFUNC && !defined(FOLLY_SANITIZE_ADDRESS)
85 __attribute__((__ifunc__("folly_popcountll_ifunc")));
87 { return popcountll_builtin(x); }
93 #endif /* !__POPCNT__ */