[libcxx-commits] [PATCH] D125958: [libc++] Use __libcpp_clz for a tighter __log2i function
Hans Wennborg via Phabricator via libcxx-commits
libcxx-commits at lists.llvm.org
Tue May 24 09:58:35 PDT 2022
hans updated this revision to Diff 431705.
hans marked an inline comment as done.
hans added a comment.
Rebase to kick the CI.
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D125958/new/
https://reviews.llvm.org/D125958
Files:
libcxx/include/__algorithm/sort.h
Index: libcxx/include/__algorithm/sort.h
===================================================================
--- libcxx/include/__algorithm/sort.h
+++ libcxx/include/__algorithm/sort.h
@@ -14,6 +14,7 @@
#include <__algorithm/min_element.h>
#include <__algorithm/partial_sort.h>
#include <__algorithm/unwrap_iter.h>
+#include <__bits>
#include <__config>
#include <__utility/swap.h>
#include <memory>
@@ -498,6 +499,15 @@
template <typename _Number>
inline _LIBCPP_HIDE_FROM_ABI _Number __log2i(_Number __n) {
+ if (__n == 0)
+ return 0;
+ if (sizeof(__n) <= sizeof(unsigned))
+ return sizeof(unsigned) * __CHAR_BIT__ - 1 - __libcpp_clz(static_cast<unsigned>(__n));
+ if (sizeof(__n) <= sizeof(unsigned long))
+ return sizeof(unsigned long) * __CHAR_BIT__ - 1 - __libcpp_clz(static_cast<unsigned long>(__n));
+ if (sizeof(__n) <= sizeof(unsigned long long))
+ return sizeof(unsigned long long) * __CHAR_BIT__ - 1 - __libcpp_clz(static_cast<unsigned long long>(__n));
+
_Number __log2 = 0;
while (__n > 1) {
__log2++;
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