Countl Zero
(misc/countl_zero.hpp)

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• Last update: 2025-12-31 07:11:44+09:00
• Include: #include "misc/countl_zero.hpp"
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countl_zero

int countl_zero(T x)

先頭の連続する $0$ の個数を返します。

$x = 0$ のときはビット幅（$32$ または $64$）を返します。

Required by

• Auxiliary Tree (虚树) (graph/auxiliary_tree.hpp)
• Lowest Common Ancestor (最小共通祖先) (graph/lowest_common_ancestor.hpp)
• Topbit (misc/topbit.hpp)
• my_template.hpp
• my_template_int128.hpp

Verified with

• misc/test/bit_operation.test.cpp
• verify/graph/auxiliary_tree.test.cpp
• verify/graph/lowest_common_ancestor_1.test.cpp
• verify/graph/lowest_common_ancestor_2.test.cpp

Code

#pragma once

#if __cplusplus >= 202002L
#include <bit>
#endif

// countl_zero
// (000, 001, 010, 011, 100) -> (32, 31, 30, 30, 29)
#if __cplusplus >= 202002L
using std::countl_zero;
#else
int countl_zero(unsigned int x) {
    return x == 0 ? 32 : __builtin_clz(x);
}
int countl_zero(unsigned long long int x) {
    return x == 0 ? 64 : __builtin_clzll(x);
}
#endif
int countl_zero(int x) { return countl_zero((unsigned int)(x)); }
int countl_zero(long long int x) {
    return countl_zero((unsigned long long int)(x));
}

#line 2 "misc/countl_zero.hpp"

#if __cplusplus >= 202002L
#include <bit>
#endif

// countl_zero
// (000, 001, 010, 011, 100) -> (32, 31, 30, 30, 29)
#if __cplusplus >= 202002L
using std::countl_zero;
#else
int countl_zero(unsigned int x) {
    return x == 0 ? 32 : __builtin_clz(x);
}
int countl_zero(unsigned long long int x) {
    return x == 0 ? 64 : __builtin_clzll(x);
}
#endif
int countl_zero(int x) { return countl_zero((unsigned int)(x)); }
int countl_zero(long long int x) {
    return countl_zero((unsigned long long int)(x));
}

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