/src/boost/boost/charconv/detail/integer_search_trees.hpp

Source
// Copyright 2023 Matt Borland
// Distributed under the Boost Software License, Version 1.0.
// https://www.boost.org/LICENSE_1_0.txt

#ifndef BOOST_CHARCONV_DETAIL_INTEGER_SEARCH_TREES_HPP
#define BOOST_CHARCONV_DETAIL_INTEGER_SEARCH_TREES_HPP

// https://stackoverflow.com/questions/1489830/efficient-way-to-determine-number-of-digits-in-an-integer?page=1&tab=scoredesc#tab-top
// https://graphics.stanford.edu/~seander/bithacks.html

#include <boost/charconv/detail/config.hpp>
#include <boost/charconv/detail/emulated128.hpp>
#include <limits>
#include <array>
#include <cstdint>

namespace boost { namespace charconv { namespace detail {

// Generic solution
template <typename T>
BOOST_CHARCONV_CXX14_CONSTEXPR int num_digits(T x) noexcept
{
    int digits = 0;

    while (x)
    {
        x /= static_cast<T>(10);
        ++digits;
    }

    return digits;
}

template <>
BOOST_CHARCONV_HOST_DEVICE BOOST_CHARCONV_CXX14_CONSTEXPR int num_digits(std::uint32_t x) noexcept
{
    if (x >= UINT32_C(10000))
    {
        if (x >= UINT32_C(10000000))
        {
            if (x >= UINT32_C(100000000))
            {
                if (x >= UINT32_C(1000000000))
                {
                    return 10;
                }
                return 9;
            }
            return 8;
        }

        else if (x >= UINT32_C(100000))
        {
            if (x >= UINT32_C(1000000))
            {
                return 7;
            }
            return 6;
        }
        return 5;
    }
    else if (x >= UINT32_C(100))
    {
        if (x >= UINT32_C(1000))
        {
            return 4;
        }
        return 3;
    }
    else if (x >= UINT32_C(10))
    {
        return 2;
    }

    return 1;
}

template <>
BOOST_CHARCONV_HOST_DEVICE BOOST_CHARCONV_CXX14_CONSTEXPR int num_digits(std::uint64_t x) noexcept
{
    if (x >= UINT64_C(10000000000))
    {
        if (x >= UINT64_C(100000000000000))
        {
            if (x >= UINT64_C(10000000000000000))
            {
                if (x >= UINT64_C(100000000000000000)) 
                {
                    if (x >= UINT64_C(1000000000000000000))
                    {
                        if (x >= UINT64_C(10000000000000000000))
                        {
                            return 20;
                        }
                        return 19;
                    }
                    return 18;
                }
                return 17;
            }
            else if (x >= UINT64_C(1000000000000000))
            {
                return 16;
            }
            return 15;
        } 
        if (x >= UINT64_C(1000000000000))
        {
            if (x >= UINT64_C(10000000000000))
            {
                return 14;
            }
            return 13;
        }
        if (x >= UINT64_C(100000000000))
        {
            return 12;
        }
        return 11;
    }
    else if (x >= UINT64_C(100000))
    {
        if (x >= UINT64_C(10000000))
        {
            if (x >= UINT64_C(100000000))
            {
                if (x >= UINT64_C(1000000000))
                {
                    return 10;
                }
                return 9;
            }
            return 8;
        }
        if (x >= UINT64_C(1000000))
        {
            return 7;
        }
        return 6;
    }
    if (x >= UINT64_C(100))
    {
        if (x >= UINT64_C(1000))
        {
            if (x >= UINT64_C(10000))
            {
                return 5;
            }
            return 4;
        }
        return 3;
    }
    if (x >= UINT64_C(10))
    {
        return 2;
    }
    return 1;
}

#ifdef BOOST_MSVC
# pragma warning(push)
# pragma warning(disable: 4307) // MSVC 14.1 warns of intergral constant overflow
#endif

BOOST_CHARCONV_CXX14_CONSTEXPR int num_digits(uint128 x) noexcept
{
    if (x.high == 0)
    {
        return num_digits(x.low);
    }

    BOOST_CHARCONV_CXX14_CONSTEXPR_NO_INLINE uint128 digits_39 = static_cast<uint128>(UINT64_C(10000000000000000000)) *
                                                                 static_cast<uint128>(UINT64_C(10000000000000000000));
    uint128 current_power_of_10 = digits_39;

    for (int i = 39; i > 0; --i)
    {
        if (x >= current_power_of_10)
        {
            return i;
        }

        current_power_of_10 /= 10U;
    }

    return 1;
}

#ifdef BOOST_MSVC
# pragma warning(pop)
#endif

#ifdef BOOST_CHARCONV_HAS_INT128
static constexpr std::array<std::uint64_t, 20> powers_of_10 =
{{
    UINT64_C(1), UINT64_C(10), UINT64_C(100), UINT64_C(1000), UINT64_C(10000), UINT64_C(100000), UINT64_C(1000000), 
    UINT64_C(10000000), UINT64_C(100000000), UINT64_C(1000000000), UINT64_C(10000000000), UINT64_C(100000000000), 
    UINT64_C(1000000000000), UINT64_C(10000000000000), UINT64_C(100000000000000), UINT64_C(1000000000000000), 
    UINT64_C(10000000000000000), UINT64_C(100000000000000000), UINT64_C(1000000000000000000), UINT64_C(10000000000000000000)
}};

// Assume that if someone is using 128 bit ints they are favoring the top end of the range
// Max value is 340,282,366,920,938,463,463,374,607,431,768,211,455 (39 digits)
BOOST_CHARCONV_CXX14_CONSTEXPR int num_digits(boost::uint128_type x) noexcept
{
    // There is no literal for boost::uint128_type, so we need to calculate them using the max value of the
    // std::uint64_t powers of 10
    constexpr boost::uint128_type digits_39 = static_cast<boost::uint128_type>(UINT64_C(10000000000000000000)) * 
                                              static_cast<boost::uint128_type>(UINT64_C(10000000000000000000));

    constexpr boost::uint128_type digits_38 = digits_39 / 10;
    constexpr boost::uint128_type digits_37 = digits_38 / 10;
    constexpr boost::uint128_type digits_36 = digits_37 / 10;
    constexpr boost::uint128_type digits_35 = digits_36 / 10;
    constexpr boost::uint128_type digits_34 = digits_35 / 10;
    constexpr boost::uint128_type digits_33 = digits_34 / 10;
    constexpr boost::uint128_type digits_32 = digits_33 / 10;
    constexpr boost::uint128_type digits_31 = digits_32 / 10;
    constexpr boost::uint128_type digits_30 = digits_31 / 10;
    constexpr boost::uint128_type digits_29 = digits_30 / 10;
    constexpr boost::uint128_type digits_28 = digits_29 / 10;
    constexpr boost::uint128_type digits_27 = digits_28 / 10;
    constexpr boost::uint128_type digits_26 = digits_27 / 10;
    constexpr boost::uint128_type digits_25 = digits_26 / 10;
    constexpr boost::uint128_type digits_24 = digits_25 / 10;
    constexpr boost::uint128_type digits_23 = digits_24 / 10;
    constexpr boost::uint128_type digits_22 = digits_23 / 10;
    constexpr boost::uint128_type digits_21 = digits_22 / 10;

    return (x >= digits_39) ? 39 :
           (x >= digits_38) ? 38 :
           (x >= digits_37) ? 37 :
           (x >= digits_36) ? 36 :
           (x >= digits_35) ? 35 :
           (x >= digits_34) ? 34 :
           (x >= digits_33) ? 33 :
           (x >= digits_32) ? 32 :
           (x >= digits_31) ? 31 :
           (x >= digits_30) ? 30 :
           (x >= digits_29) ? 29 :
           (x >= digits_28) ? 28 :
           (x >= digits_27) ? 27 :
           (x >= digits_26) ? 26 :
           (x >= digits_25) ? 25 :
           (x >= digits_24) ? 24 :
           (x >= digits_23) ? 23 :
           (x >= digits_22) ? 22 :
           (x >= digits_21) ? 21 :
           (x >= powers_of_10[19]) ? 20 :
           (x >= powers_of_10[18]) ? 19 :
           (x >= powers_of_10[17]) ? 18 :
           (x >= powers_of_10[16]) ? 17 :
           (x >= powers_of_10[15]) ? 16 :
           (x >= powers_of_10[14]) ? 15 :
           (x >= powers_of_10[13]) ? 14 :
           (x >= powers_of_10[12]) ? 13 :
           (x >= powers_of_10[11]) ? 12 :
           (x >= powers_of_10[10]) ? 11 :
           (x >= powers_of_10[9])  ? 10 :
           (x >= powers_of_10[8])  ?  9 :
           (x >= powers_of_10[7])  ?  8 :
           (x >= powers_of_10[6])  ?  7 :
           (x >= powers_of_10[5])  ?  6 :
           (x >= powers_of_10[4])  ?  5 :
           (x >= powers_of_10[3])  ?  4 :
           (x >= powers_of_10[2])  ?  3 :
           (x >= powers_of_10[1])  ?  2 :
           (x >= powers_of_10[0])  ?  1 : 0;
}
#endif

}}} // Namespace boost::charconv::detail

#endif // BOOST_CHARCONV_DETAIL_INTEGER_SEARCH_TREES_HPP

Coverage Report

Created: 2026-09-13 07:10

Line	Count	Source
1		// Copyright 2023 Matt Borland
2		// Distributed under the Boost Software License, Version 1.0.
3		// https://www.boost.org/LICENSE_1_0.txt
4
5		#ifndef BOOST_CHARCONV_DETAIL_INTEGER_SEARCH_TREES_HPP
6		#define BOOST_CHARCONV_DETAIL_INTEGER_SEARCH_TREES_HPP
7
8		// https://stackoverflow.com/questions/1489830/efficient-way-to-determine-number-of-digits-in-an-integer?page=1&tab=scoredesc#tab-top
9		// https://graphics.stanford.edu/~seander/bithacks.html
10
11		#include <boost/charconv/detail/config.hpp>
12		#include <boost/charconv/detail/emulated128.hpp>
13		#include <limits>
14		#include <array>
15		#include <cstdint>
16
17		namespace boost { namespace charconv { namespace detail {
18
19		// Generic solution
20		template <typename T>
21		BOOST_CHARCONV_CXX14_CONSTEXPR int num_digits(T x) noexcept
22	3.96M	{
23	3.96M	int digits = 0;
24
25	11.8M	while (x)
26	7.85M	{
27	7.85M	x /= static_cast<T>(10);
28	7.85M	++digits;
29	7.85M	}
30
31	3.96M	return digits;
32	3.96M	}
33
34		template <>
35		BOOST_CHARCONV_HOST_DEVICE BOOST_CHARCONV_CXX14_CONSTEXPR int num_digits(std::uint32_t x) noexcept
36	0	{
37	0	if (x >= UINT32_C(10000))
38	0	{
39	0	if (x >= UINT32_C(10000000))
40	0	{
41	0	if (x >= UINT32_C(100000000))
42	0	{
43	0	if (x >= UINT32_C(1000000000))
44	0	{
45	0	return 10;
46	0	}
47	0	return 9;
48	0	}
49	0	return 8;
50	0	}
51
52	0	else if (x >= UINT32_C(100000))
53	0	{
54	0	if (x >= UINT32_C(1000000))
55	0	{
56	0	return 7;
57	0	}
58	0	return 6;
59	0	}
60	0	return 5;
61	0	}
62	0	else if (x >= UINT32_C(100))
63	0	{
64	0	if (x >= UINT32_C(1000))
65	0	{
66	0	return 4;
67	0	}
68	0	return 3;
69	0	}
70	0	else if (x >= UINT32_C(10))
71	0	{
72	0	return 2;
73	0	}
74
75	0	return 1;
76	0	}
77
78		template <>
79		BOOST_CHARCONV_HOST_DEVICE BOOST_CHARCONV_CXX14_CONSTEXPR int num_digits(std::uint64_t x) noexcept
80	0	{
81	0	if (x >= UINT64_C(10000000000))
82	0	{
83	0	if (x >= UINT64_C(100000000000000))
84	0	{
85	0	if (x >= UINT64_C(10000000000000000))
86	0	{
87	0	if (x >= UINT64_C(100000000000000000))
88	0	{
89	0	if (x >= UINT64_C(1000000000000000000))
90	0	{
91	0	if (x >= UINT64_C(10000000000000000000))
92	0	{
93	0	return 20;
94	0	}
95	0	return 19;
96	0	}
97	0	return 18;
98	0	}
99	0	return 17;
100	0	}
101	0	else if (x >= UINT64_C(1000000000000000))
102	0	{
103	0	return 16;
104	0	}
105	0	return 15;
106	0	}
107	0	if (x >= UINT64_C(1000000000000))
108	0	{
109	0	if (x >= UINT64_C(10000000000000))
110	0	{
111	0	return 14;
112	0	}
113	0	return 13;
114	0	}
115	0	if (x >= UINT64_C(100000000000))
116	0	{
117	0	return 12;
118	0	}
119	0	return 11;
120	0	}
121	0	else if (x >= UINT64_C(100000))
122	0	{
123	0	if (x >= UINT64_C(10000000))
124	0	{
125	0	if (x >= UINT64_C(100000000))
126	0	{
127	0	if (x >= UINT64_C(1000000000))
128	0	{
129	0	return 10;
130	0	}
131	0	return 9;
132	0	}
133	0	return 8;
134	0	}
135	0	if (x >= UINT64_C(1000000))
136	0	{
137	0	return 7;
138	0	}
139	0	return 6;
140	0	}
141	0	if (x >= UINT64_C(100))
142	0	{
143	0	if (x >= UINT64_C(1000))
144	0	{
145	0	if (x >= UINT64_C(10000))
146	0	{
147	0	return 5;
148	0	}
149	0	return 4;
150	0	}
151	0	return 3;
152	0	}
153	0	if (x >= UINT64_C(10))
154	0	{
155	0	return 2;
156	0	}
157	0	return 1;
158	0	}
159
160		#ifdef BOOST_MSVC
161		# pragma warning(push)
162		# pragma warning(disable: 4307) // MSVC 14.1 warns of intergral constant overflow
163		#endif
164
165		BOOST_CHARCONV_CXX14_CONSTEXPR int num_digits(uint128 x) noexcept
166	0	{
167	0	if (x.high == 0)
168	0	{
169	0	return num_digits(x.low);
170	0	}
171	0
172	0	BOOST_CHARCONV_CXX14_CONSTEXPR_NO_INLINE uint128 digits_39 = static_cast<uint128>(UINT64_C(10000000000000000000)) *
173	0	static_cast<uint128>(UINT64_C(10000000000000000000));
174	0	uint128 current_power_of_10 = digits_39;
175	0
176	0	for (int i = 39; i > 0; --i)
177	0	{
178	0	if (x >= current_power_of_10)
179	0	{
180	0	return i;
181	0	}
182	0
183	0	current_power_of_10 /= 10U;
184	0	}
185	0
186	0	return 1;
187	0	}
188
189		#ifdef BOOST_MSVC
190		# pragma warning(pop)
191		#endif
192
193		#ifdef BOOST_CHARCONV_HAS_INT128
194		static constexpr std::array<std::uint64_t, 20> powers_of_10 =
195		{{
196		UINT64_C(1), UINT64_C(10), UINT64_C(100), UINT64_C(1000), UINT64_C(10000), UINT64_C(100000), UINT64_C(1000000),
197		UINT64_C(10000000), UINT64_C(100000000), UINT64_C(1000000000), UINT64_C(10000000000), UINT64_C(100000000000),
198		UINT64_C(1000000000000), UINT64_C(10000000000000), UINT64_C(100000000000000), UINT64_C(1000000000000000),
199		UINT64_C(10000000000000000), UINT64_C(100000000000000000), UINT64_C(1000000000000000000), UINT64_C(10000000000000000000)
200		}};
201
202		// Assume that if someone is using 128 bit ints they are favoring the top end of the range
203		// Max value is 340,282,366,920,938,463,463,374,607,431,768,211,455 (39 digits)
204		BOOST_CHARCONV_CXX14_CONSTEXPR int num_digits(boost::uint128_type x) noexcept
205	0	{
206		// There is no literal for boost::uint128_type, so we need to calculate them using the max value of the
207		// std::uint64_t powers of 10
208	0	constexpr boost::uint128_type digits_39 = static_cast<boost::uint128_type>(UINT64_C(10000000000000000000)) *
209	0	static_cast<boost::uint128_type>(UINT64_C(10000000000000000000));
210
211	0	constexpr boost::uint128_type digits_38 = digits_39 / 10;
212	0	constexpr boost::uint128_type digits_37 = digits_38 / 10;
213	0	constexpr boost::uint128_type digits_36 = digits_37 / 10;
214	0	constexpr boost::uint128_type digits_35 = digits_36 / 10;
215	0	constexpr boost::uint128_type digits_34 = digits_35 / 10;
216	0	constexpr boost::uint128_type digits_33 = digits_34 / 10;
217	0	constexpr boost::uint128_type digits_32 = digits_33 / 10;
218	0	constexpr boost::uint128_type digits_31 = digits_32 / 10;
219	0	constexpr boost::uint128_type digits_30 = digits_31 / 10;
220	0	constexpr boost::uint128_type digits_29 = digits_30 / 10;
221	0	constexpr boost::uint128_type digits_28 = digits_29 / 10;
222	0	constexpr boost::uint128_type digits_27 = digits_28 / 10;
223	0	constexpr boost::uint128_type digits_26 = digits_27 / 10;
224	0	constexpr boost::uint128_type digits_25 = digits_26 / 10;
225	0	constexpr boost::uint128_type digits_24 = digits_25 / 10;
226	0	constexpr boost::uint128_type digits_23 = digits_24 / 10;
227	0	constexpr boost::uint128_type digits_22 = digits_23 / 10;
228	0	constexpr boost::uint128_type digits_21 = digits_22 / 10;
229
230	0	return (x >= digits_39) ? 39 :
231	0	(x >= digits_38) ? 38 :
232	0	(x >= digits_37) ? 37 :
233	0	(x >= digits_36) ? 36 :
234	0	(x >= digits_35) ? 35 :
235	0	(x >= digits_34) ? 34 :
236	0	(x >= digits_33) ? 33 :
237	0	(x >= digits_32) ? 32 :
238	0	(x >= digits_31) ? 31 :
239	0	(x >= digits_30) ? 30 :
240	0	(x >= digits_29) ? 29 :
241	0	(x >= digits_28) ? 28 :
242	0	(x >= digits_27) ? 27 :
243	0	(x >= digits_26) ? 26 :
244	0	(x >= digits_25) ? 25 :
245	0	(x >= digits_24) ? 24 :
246	0	(x >= digits_23) ? 23 :
247	0	(x >= digits_22) ? 22 :
248	0	(x >= digits_21) ? 21 :
249	0	(x >= powers_of_10[19]) ? 20 :
250	0	(x >= powers_of_10[18]) ? 19 :
251	0	(x >= powers_of_10[17]) ? 18 :
252	0	(x >= powers_of_10[16]) ? 17 :
253	0	(x >= powers_of_10[15]) ? 16 :
254	0	(x >= powers_of_10[14]) ? 15 :
255	0	(x >= powers_of_10[13]) ? 14 :
256	0	(x >= powers_of_10[12]) ? 13 :
257	0	(x >= powers_of_10[11]) ? 12 :
258	0	(x >= powers_of_10[10]) ? 11 :
259	0	(x >= powers_of_10[9]) ? 10 :
260	0	(x >= powers_of_10[8]) ? 9 :
261	0	(x >= powers_of_10[7]) ? 8 :
262	0	(x >= powers_of_10[6]) ? 7 :
263	0	(x >= powers_of_10[5]) ? 6 :
264	0	(x >= powers_of_10[4]) ? 5 :
265	0	(x >= powers_of_10[3]) ? 4 :
266	0	(x >= powers_of_10[2]) ? 3 :
267	0	(x >= powers_of_10[1]) ? 2 :
268	0	(x >= powers_of_10[0]) ? 1 : 0;
269	0	}
270		#endif
271
272		}}} // Namespace boost::charconv::detail
273
274		#endif // BOOST_CHARCONV_DETAIL_INTEGER_SEARCH_TREES_HPP