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made HashFnv functions constexpr (#4640)

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* added FLATBUFFERS_CONSTEXPR_CPP14 define for C++14 and above constexpr

* made HashFnv functions constexpr (depending on FLATBUFFERS_CONSTEXPR)
This commit is contained in:
Christian Helmich
2018-03-03 02:13:55 +09:00
committed by Wouter van Oortmerssen
parent 48d8232584
commit ec74f58b94
2 changed files with 11 additions and 4 deletions
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8
include/flatbuffers/hash.h
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@@ -39,7 +39,7 @@ template<> struct FnvTraits<uint64_t> {
static const uint64_t kOffsetBasis = 0xcbf29ce484222645ULL;
};
template<typename T> T HashFnv1(const char *input) {
template<typename T> FLATBUFFERS_CONSTEXPR_CPP14 T HashFnv1(const char *input) {
T hash = FnvTraits<T>::kOffsetBasis;
for (const char *c = input; *c; ++c) {
hash *= FnvTraits<T>::kFnvPrime;
@@ -48,7 +48,7 @@ template<typename T> T HashFnv1(const char *input) {
return hash;
}
template<typename T> T HashFnv1a(const char *input) {
template<typename T> FLATBUFFERS_CONSTEXPR_CPP14 T HashFnv1a(const char *input) {
T hash = FnvTraits<T>::kOffsetBasis;
for (const char *c = input; *c; ++c) {
hash ^= static_cast<unsigned char>(*c);
@@ -57,12 +57,12 @@ template<typename T> T HashFnv1a(const char *input) {
return hash;
}
template <> inline uint16_t HashFnv1<uint16_t>(const char *input) {
template <> FLATBUFFERS_CONSTEXPR_CPP14 inline uint16_t HashFnv1<uint16_t>(const char *input) {
uint32_t hash = HashFnv1<uint32_t>(input);
return (hash >> 16) ^ (hash & 0xffff);
}
template <> inline uint16_t HashFnv1a<uint16_t>(const char *input) {
template <> FLATBUFFERS_CONSTEXPR_CPP14 inline uint16_t HashFnv1a<uint16_t>(const char *input) {
uint32_t hash = HashFnv1a<uint32_t>(input);
return (hash >> 16) ^ (hash & 0xffff);
}