20209445534

Committed 14 Dec 2025 02:31PM UTC coverage: 90.361% (+0.004%) from 90.357%

Build # 20209445534

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Commit Message

Merge pull request #5176 from randombit/jack/div10

Add a helper for integer division by 10

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92.05

/src/lib/math/bigint/big_code.cpp

/*
* BigInt Encoding/Decoding
* (C) 1999-2010,2012,2019,2021 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/

#include <botan/bigint.h>

#include <botan/hex.h>
#include <botan/mem_ops.h>
#include <botan/internal/divide.h>
#include <botan/internal/mp_core.h>
#include <botan/internal/stl_util.h>

namespace Botan {

namespace {

consteval word decimal_conversion_radix() {
   if constexpr(sizeof(word) == 8) {
      return 10000000000000000000U;
   } else {
      return 1000000000U;
   }
}

consteval size_t decimal_conversion_radix_digits() {
   if constexpr(sizeof(word) == 8) {
      return 19;
   } else {
      return 9;
   }
}

}  // namespace

std::string BigInt::to_dec_string() const {
   // Use the largest power of 10 that fits in a word
   constexpr word conversion_radix = decimal_conversion_radix();
   constexpr size_t radix_digits = decimal_conversion_radix_digits();

   // (over-)estimate of the number of digits needed; log2(10) ~ 3.3219
   const size_t digit_estimate = static_cast<size_t>(1 + (static_cast<double>(this->bits()) / 3.32));

   // (over-)estimate of db such that conversion_radix^db > *this
   const size_t digit_blocks = (digit_estimate + radix_digits - 1) / radix_digits;

   BigInt value = *this;
   value.set_sign(Positive);

   // Extract groups of digits into words
   std::vector<word> digit_groups(digit_blocks);

   for(size_t i = 0; i != digit_blocks; ++i) {
      word remainder = 0;
      ct_divide_word(value, conversion_radix, value, remainder);
      digit_groups[i] = remainder;
   }

   BOTAN_ASSERT_NOMSG(value.is_zero());

   // Extract digits from the groups
   std::vector<uint8_t> digits(digit_blocks * radix_digits);

   for(size_t i = 0; i != digit_blocks; ++i) {
      word remainder = digit_groups[i];
      for(size_t j = 0; j != radix_digits; ++j) {
         const word new_remainder = divide_10(remainder);
         const word digit = remainder - new_remainder * 10;
         digits[radix_digits * i + j] = static_cast<uint8_t>(digit);
         remainder = new_remainder;
      }
   }

   // remove leading zeros
   while(!digits.empty() && digits.back() == 0) {
      digits.pop_back();
   }

   BOTAN_ASSERT_NOMSG(digit_estimate >= digits.size());

   // Reverse the digits to big-endian and format to text
   std::string s;
   s.reserve(1 + digits.size());

   if(is_negative()) {
      s += "-";
   }

   // Reverse and convert to textual digits
   // TODO(Botan4) use std::ranges::reverse_view here once available (need newer Clang)
   // NOLINTNEXTLINE(modernize-loop-convert)
   for(auto i = digits.rbegin(); i != digits.rend(); ++i) {
      s.push_back(*i + '0');  // assumes ASCII
   }

   if(s.empty()) {
      s += "0";
   }

   return s;
}

std::string BigInt::to_hex_string() const {
   const size_t this_bytes = this->bytes();
   std::vector<uint8_t> bits(std::max<size_t>(1, this_bytes));

   if(this_bytes > 0) {
      this->serialize_to(bits);
   }

   std::string hrep;
   if(is_negative()) {
      hrep += "-";
   }
   hrep += "0x";
   hrep += hex_encode(bits);
   return hrep;
}

/*
* Encode two BigInt, with leading 0s if needed, and concatenate
*/
secure_vector<uint8_t> BigInt::encode_fixed_length_int_pair(const BigInt& n1, const BigInt& n2, size_t bytes) {
   if(n1.is_negative() || n2.is_negative()) {
      throw Encoding_Error("encode_fixed_length_int_pair: values must be positive");
   }
   if(n1.bytes() > bytes || n2.bytes() > bytes) {
      throw Encoding_Error("encode_fixed_length_int_pair: values too large to encode properly");
   }
   secure_vector<uint8_t> output(2 * bytes);
   BufferStuffer stuffer(output);
   n1.serialize_to(stuffer.next(bytes));
   n2.serialize_to(stuffer.next(bytes));
   return output;
}

BigInt BigInt::decode(std::span<const uint8_t> buf, Base base) {
   if(base == Binary) {
      return BigInt::from_bytes(buf);
   }
   return BigInt::decode(buf.data(), buf.size(), base);
}

/*
* Decode a BigInt
*/
BigInt BigInt::decode(const uint8_t buf[], size_t length, Base base) {
   if(base == Binary) {
      return BigInt::from_bytes(std::span{buf, length});
   } else if(base == Hexadecimal) {
      BigInt r;
      secure_vector<uint8_t> binary;

      if(length % 2 == 1) {
         // Handle lack of leading 0
         const char buf0_with_leading_0[2] = {'0', static_cast<char>(buf[0])};

         binary = hex_decode_locked(buf0_with_leading_0, 2);

         if(length > 1) {
            binary += hex_decode_locked(cast_uint8_ptr_to_char(&buf[1]), length - 1, false);
         }
      } else {
         binary = hex_decode_locked(cast_uint8_ptr_to_char(buf), length, false);
      }

      r.assign_from_bytes(binary);
      return r;
   } else if(base == Decimal) {
      BigInt r;
      // This could be made faster using the same trick as to_dec_string
      for(size_t i = 0; i != length; ++i) {
         const char c = buf[i];

         if(c < '0' || c > '9') {
            throw Invalid_Argument("BigInt::decode: invalid decimal char");
         }

         const uint8_t x = c - '0';
         BOTAN_ASSERT_NOMSG(x < 10);

         r *= 10;
         r += x;
      }
      return r;
   } else {
      throw Invalid_Argument("Unknown BigInt decoding method");
   }
}

}  // namespace Botan

1	/*
2	* BigInt Encoding/Decoding
3	* (C) 1999-2010,2012,2019,2021 Jack Lloyd
4	*
5	* Botan is released under the Simplified BSD License (see license.txt)
6	*/
7
8	#include <botan/bigint.h>
9
10	#include <botan/hex.h>
11	#include <botan/mem_ops.h>
12	#include <botan/internal/divide.h>
13	#include <botan/internal/mp_core.h>
14	#include <botan/internal/stl_util.h>
15
16	namespace Botan {
17
18	namespace {
19
20	consteval word decimal_conversion_radix() {
21	if constexpr(sizeof(word) == 8) {
22	return 10000000000000000000U;
23	} else {
24	return 1000000000U;
25	}
26	}
27
28	consteval size_t decimal_conversion_radix_digits() {
29	if constexpr(sizeof(word) == 8) {
30	return 19;
31	} else {
32	return 9;
33	}
34	}
35
36	} // namespace
37
38	std::string BigInt::to_dec_string() const {	60✔
39	// Use the largest power of 10 that fits in a word
40	constexpr word conversion_radix = decimal_conversion_radix();	60✔
41	constexpr size_t radix_digits = decimal_conversion_radix_digits();	60✔
42
43	// (over-)estimate of the number of digits needed; log2(10) ~ 3.3219
44	const size_t digit_estimate = static_cast<size_t>(1 + (static_cast<double>(this->bits()) / 3.32));	60✔
45
46	// (over-)estimate of db such that conversion_radix^db > *this
47	const size_t digit_blocks = (digit_estimate + radix_digits - 1) / radix_digits;	60✔
48
49	BigInt value = *this;	60✔
50	value.set_sign(Positive);	60✔
51
52	// Extract groups of digits into words
53	std::vector<word> digit_groups(digit_blocks);	60✔
54
55	for(size_t i = 0; i != digit_blocks; ++i) {	132✔
56	word remainder = 0;	72✔
57	ct_divide_word(value, conversion_radix, value, remainder);	72✔
58	digit_groups[i] = remainder;	72✔
59	}
60
61	BOTAN_ASSERT_NOMSG(value.is_zero());	120✔
62
63	// Extract digits from the groups
64	std::vector<uint8_t> digits(digit_blocks * radix_digits);	60✔
65
66	for(size_t i = 0; i != digit_blocks; ++i) {	132✔
67	word remainder = digit_groups[i];	72✔
68	for(size_t j = 0; j != radix_digits; ++j) {	1,440✔
69	const word new_remainder = divide_10(remainder);	1,368✔
70	const word digit = remainder - new_remainder * 10;	1,368✔
71	digits[radix_digits * i + j] = static_cast<uint8_t>(digit);	1,368✔
72	remainder = new_remainder;	1,368✔
73	}
74	}
75
76	// remove leading zeros
77	while(!digits.empty() && digits.back() == 0) {	960✔
78	digits.pop_back();	900✔
79	}
80
81	BOTAN_ASSERT_NOMSG(digit_estimate >= digits.size());	60✔
82
83	// Reverse the digits to big-endian and format to text
84	std::string s;	60✔
85	s.reserve(1 + digits.size());	60✔
86
87	if(is_negative()) {	60✔
88	s += "-";	5✔
89	}
90
91	// Reverse and convert to textual digits
92	// TODO(Botan4) use std::ranges::reverse_view here once available (need newer Clang)
93	// NOLINTNEXTLINE(modernize-loop-convert)
94	for(auto i = digits.rbegin(); i != digits.rend(); ++i) {	528✔
95	s.push_back(*i + '0'); // assumes ASCII	468✔
96	}
97
98	if(s.empty()) {	60✔
99	s += "0";	6✔
100	}
101
102	return s;	120✔
103	}	120✔
104
105	std::string BigInt::to_hex_string() const {	85✔
106	const size_t this_bytes = this->bytes();	85✔
107	std::vector<uint8_t> bits(std::max<size_t>(1, this_bytes));	143✔
108
109	if(this_bytes > 0) {	85✔
110	this->serialize_to(bits);	83✔
111	}
112
113	std::string hrep;	85✔
114	if(is_negative()) {	85✔
115	hrep += "-";	5✔
116	}
117	hrep += "0x";	85✔
118	hrep += hex_encode(bits);	170✔
119	return hrep;	85✔
120	}	85✔
121
122	/*
123	* Encode two BigInt, with leading 0s if needed, and concatenate
124	*/
125	secure_vector<uint8_t> BigInt::encode_fixed_length_int_pair(const BigInt& n1, const BigInt& n2, size_t bytes) {	97✔
126	if(n1.is_negative() \|\| n2.is_negative()) {	97✔
127	throw Encoding_Error("encode_fixed_length_int_pair: values must be positive");	×
128	}
129	if(n1.bytes() > bytes \|\| n2.bytes() > bytes) {	97✔
130	throw Encoding_Error("encode_fixed_length_int_pair: values too large to encode properly");	×
131	}
132	secure_vector<uint8_t> output(2 * bytes);	97✔
133	BufferStuffer stuffer(output);	97✔
134	n1.serialize_to(stuffer.next(bytes));	97✔
135	n2.serialize_to(stuffer.next(bytes));	97✔
136	return output;	97✔
137	}	×
138
139	BigInt BigInt::decode(std::span<const uint8_t> buf, Base base) {	46,674✔
140	if(base == Binary) {	46,674✔
141	return BigInt::from_bytes(buf);	×
142	}
143	return BigInt::decode(buf.data(), buf.size(), base);	46,674✔
144	}
145
146	/*
147	* Decode a BigInt
148	*/
149	BigInt BigInt::decode(const uint8_t buf[], size_t length, Base base) {	46,674✔
150	if(base == Binary) {	46,674✔
151	return BigInt::from_bytes(std::span{buf, length});	×
152	} else if(base == Hexadecimal) {	46,674✔
153	BigInt r;	42,407✔
154	secure_vector<uint8_t> binary;	42,407✔
155
156	if(length % 2 == 1) {	42,407✔
157	// Handle lack of leading 0
158	const char buf0_with_leading_0[2] = {'0', static_cast<char>(buf[0])};	4,236✔
159
160	binary = hex_decode_locked(buf0_with_leading_0, 2);	8,472✔
161
162	if(length > 1) {	4,236✔
163	binary += hex_decode_locked(cast_uint8_ptr_to_char(&buf[1]), length - 1, false);	6,100✔
164	}
165	} else {
166	binary = hex_decode_locked(cast_uint8_ptr_to_char(buf), length, false);	76,342✔
167	}
168
169	r.assign_from_bytes(binary);	42,407✔
170	return r;	42,407✔
171	} else if(base == Decimal) {	46,674✔
172	BigInt r;	4,267✔
173	// This could be made faster using the same trick as to_dec_string
174	for(size_t i = 0; i != length; ++i) {	382,960✔
175	const char c = buf[i];	378,693✔
176
177	if(c < '0' \|\| c > '9') {	378,693✔
178	throw Invalid_Argument("BigInt::decode: invalid decimal char");	×
179	}
180
181	const uint8_t x = c - '0';	378,693✔
182	BOTAN_ASSERT_NOMSG(x < 10);	378,693✔
183
184	r *= 10;	378,693✔
185	r += x;	378,693✔
186	}
187	return r;	4,267✔
188	} else {	4,267✔
189	throw Invalid_Argument("Unknown BigInt decoding method");	×
190	}
191	}
192
193	} // namespace Botan

randombit / botan / 20209445534

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