Make find_first_set works on x86 MSVC (#38637)
Summary:
Fixes https://github.com/pytorch/pytorch/issues/38322#issuecomment-630031072.
Tested locally.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/38637
Differential Revision: D21620059
Pulled By: ezyang
fbshipit-source-id: 50af50ce29e46759f11a196fa0fedca2740214bb
diff --git a/c10/util/Bitset.h b/c10/util/Bitset.h
index 5510cfc..835fe6d 100644
--- a/c10/util/Bitset.h
+++ b/c10/util/Bitset.h
@@ -77,13 +77,29 @@
// (i.e. if the very first bit is set, this function returns '1'), and a return
// of '0' means that there was no bit set.
size_t find_first_set() const {
- #if defined(_MSC_VER)
+ #if defined(_MSC_VER) && defined(_M_X64)
unsigned long result;
bool has_bits_set = (0 != _BitScanForward64(&result, bitset_));
if (!has_bits_set) {
return 0;
}
return result + 1;
+ #elif defined(_MSC_VER) && defined(_M_IX86)
+ unsigned long result;
+ if (static_cast<uint32_t>(bitset_) != 0) {
+ bool has_bits_set = (0 != _BitScanForward(&result, static_cast<uint32_t>(bitset_)));
+ if (!has_bits_set) {
+ return 0;
+ }
+ return result + 1;
+ }
+ else {
+ bool has_bits_set = (0 != _BitScanForward(&result, static_cast<uint32_t>(bitset_ >> 32)));
+ if (!has_bits_set) {
+ return 0;
+ }
+ return result + 33;
+ }
#else
return __builtin_ffsll(bitset_);
#endif
