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doc + test: Correct uint256 hex string endianness
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Follow-up to bitcoin#30436.

uint256 string representation was wrongfully documented as little-endian due to them being reversed by GetHex() etc, and base_blob::Compare() giving most significance to the beginning of the internal array. They are closer to "big-endian", but this commit tries to be even more precise than that.

uint256_tests.cpp - Avoid using variable from the left side of the condition in the right side.

setup_common.cpp - Skip needless ArithToUint256-conversion.
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@hodlinator
hodlinator committed Aug 3, 2024
1 parent 5d28013 commit 73e3fa1
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Showing 5 changed files with 70 additions and 23 deletions.
2 changes: 2 additions & 0 deletions src/arith_uint256.h
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Original file line number Diff line number Diff line change
Expand Up @@ -196,6 +196,7 @@ class base_uint
return ret;
}

/** Numeric ordering (unlike \ref base_blob::Compare) */
int CompareTo(const base_uint& b) const;
bool EqualTo(uint64_t b) const;

Expand All @@ -218,6 +219,7 @@ class base_uint
friend inline bool operator==(const base_uint& a, uint64_t b) { return a.EqualTo(b); }
friend inline bool operator!=(const base_uint& a, uint64_t b) { return !a.EqualTo(b); }

/** Hex encoding of the number (with the most significant digits first). */
std::string GetHex() const;
std::string ToString() const;

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11 changes: 10 additions & 1 deletion src/test/arith_uint256_tests.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -3,6 +3,7 @@
// file COPYING or http://www.opensource.org/licenses/mit-license.php.

#include <arith_uint256.h>
#include <test/util/setup_common.h>
#include <uint256.h>

#include <boost/test/unit_test.hpp>
Expand All @@ -22,7 +23,8 @@ static inline arith_uint256 arith_uint256V(const std::vector<unsigned char>& vch
{
return UintToArith256(uint256(vch));
}
static inline arith_uint256 arith_uint256S(const std::string& str) { return UintToArith256(uint256S(str)); }
// Takes a number written in hex (with most significant digits first).
static inline arith_uint256 arith_uint256S(std::string_view str) { return UintToArith256(uint256S(str)); }

const unsigned char R1Array[] =
"\x9c\x52\x4a\xdb\xcf\x56\x11\x12\x2b\x29\x12\x5e\x5d\x35\xd2\xd2"
Expand Down Expand Up @@ -104,6 +106,7 @@ BOOST_AUTO_TEST_CASE( basics ) // constructors, equality, inequality
BOOST_CHECK(arith_uint256S(R1L.ToString()) == R1L);
BOOST_CHECK(arith_uint256S(" 0x" + R1L.ToString() + " ") == R1L);
BOOST_CHECK(arith_uint256S("") == ZeroL);
BOOST_CHECK(arith_uint256S("1") == OneL);
BOOST_CHECK(R1L == arith_uint256S(R1ArrayHex));
BOOST_CHECK(arith_uint256(R1L) == R1L);
BOOST_CHECK((arith_uint256(R1L^R2L)^R2L) == R1L);
Expand Down Expand Up @@ -278,6 +281,12 @@ BOOST_AUTO_TEST_CASE( comparison ) // <= >= < >
BOOST_CHECK( R1L <= TmpL ); BOOST_CHECK( (R1L == TmpL) != (R1L < TmpL)); BOOST_CHECK( (TmpL == R1L) || !( R1L >= TmpL));
BOOST_CHECK(! (TmpL < R1L)); BOOST_CHECK(! (R1L > TmpL));
}

BOOST_CHECK_LT(ZeroL,
OneL);
// Verify hex number representation has the most significant digits first.
BOOST_CHECK_LT(arith_uint256S("0000000000000000000000000000000000000000000000000000000000000001"),
arith_uint256S("1000000000000000000000000000000000000000000000000000000000000000"));
}

BOOST_AUTO_TEST_CASE( plusMinus )
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41 changes: 24 additions & 17 deletions src/test/uint256_tests.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -58,7 +58,7 @@ static std::string ArrayToString(const unsigned char A[], unsigned int width)
return Stream.str();
}

// Input is treated as little-endian.
// Takes hex string in reverse byte order.
inline uint160 uint160S(std::string_view str)
{
uint160 rv;
Expand Down Expand Up @@ -99,6 +99,7 @@ BOOST_AUTO_TEST_CASE( basics ) // constructors, equality, inequality
BOOST_CHECK_EQUAL(uint256S(" 0x"+R1L.ToString()+"-trash;%^& "), R1L);
BOOST_CHECK_EQUAL(uint256S("\t \n \n \f\n\r\t\v\t 0x"+R1L.ToString()+" \t \n \n \f\n\r\t\v\t "), R1L);
BOOST_CHECK_EQUAL(uint256S(""), ZeroL);
BOOST_CHECK_EQUAL(uint256S("1"), OneL);
BOOST_CHECK_EQUAL(R1L, uint256S(R1ArrayHex));
BOOST_CHECK_EQUAL(uint256(R1L), R1L);
BOOST_CHECK_EQUAL(uint256(ZeroL), ZeroL);
Expand Down Expand Up @@ -152,9 +153,15 @@ BOOST_AUTO_TEST_CASE( comparison ) // <= >= < >
BOOST_CHECK_LT(R1S, MaxS);
BOOST_CHECK_LT(R2S, MaxS);

// Verify hex strings are little-endian
BOOST_CHECK_LT(uint256S("2000000000000000000000000000000000000000000000000000000000000001"),
uint256S("1000000000000000000000000000000000000000000000000000000000000002"));
// Non-arithmetic uint256s compare from the beginning of their inner arrays:
BOOST_CHECK_LT(R2L, R1L);
// Ensure first element comparisons give the same order as above:
BOOST_CHECK_LT(*R2L.begin(), *R1L.begin());
// Ensure last element comparisons give a different result (swapped params):
BOOST_CHECK_LT(*(R1L.end()-1), *(R2L.end()-1));
// Hex strings represent reverse-encoded bytes, with lexicographic ordering:
BOOST_CHECK_LT(uint256S("1000000000000000000000000000000000000000000000000000000000000000"),
uint256S("0000000000000000000000000000000000000000000000000000000000000001"));
}

BOOST_AUTO_TEST_CASE(methods) // GetHex SetHexDeprecated FromHex begin() end() size() GetLow64 GetSerializeSize, Serialize, Unserialize
Expand All @@ -172,11 +179,11 @@ BOOST_AUTO_TEST_CASE(methods) // GetHex SetHexDeprecated FromHex begin() end() s
BOOST_CHECK_EQUAL(uint256::FromHex(ZeroL.ToString()).value(), uint256());

TmpL = uint256::FromHex(R1L.ToString()).value();
BOOST_CHECK_EQUAL_COLLECTIONS(R1L.begin(), R1L.end(), R1Array, R1Array + R1L.size());
BOOST_CHECK_EQUAL_COLLECTIONS(TmpL.begin(), TmpL.end(), R1Array, R1Array + TmpL.size());
BOOST_CHECK_EQUAL_COLLECTIONS(R2L.begin(), R2L.end(), R2Array, R2Array + R2L.size());
BOOST_CHECK_EQUAL_COLLECTIONS(ZeroL.begin(), ZeroL.end(), ZeroArray, ZeroArray + ZeroL.size());
BOOST_CHECK_EQUAL_COLLECTIONS(OneL.begin(), OneL.end(), OneArray, OneArray + OneL.size());
BOOST_CHECK_EQUAL_COLLECTIONS(R1L.begin(), R1L.end(), R1Array, R1Array + uint256::size());
BOOST_CHECK_EQUAL_COLLECTIONS(TmpL.begin(), TmpL.end(), R1Array, R1Array + uint256::size());
BOOST_CHECK_EQUAL_COLLECTIONS(R2L.begin(), R2L.end(), R2Array, R2Array + uint256::size());
BOOST_CHECK_EQUAL_COLLECTIONS(ZeroL.begin(), ZeroL.end(), ZeroArray, ZeroArray + uint256::size());
BOOST_CHECK_EQUAL_COLLECTIONS(OneL.begin(), OneL.end(), OneArray, OneArray + uint256::size());
BOOST_CHECK_EQUAL(R1L.size(), sizeof(R1L));
BOOST_CHECK_EQUAL(sizeof(R1L), 32);
BOOST_CHECK_EQUAL(R1L.size(), 32);
Expand Down Expand Up @@ -218,11 +225,11 @@ BOOST_AUTO_TEST_CASE(methods) // GetHex SetHexDeprecated FromHex begin() end() s
BOOST_CHECK_EQUAL(uint160::FromHex(ZeroS.ToString()).value(), uint160());

TmpS = uint160::FromHex(R1S.ToString()).value();
BOOST_CHECK_EQUAL_COLLECTIONS(R1S.begin(), R1S.end(), R1Array, R1Array + R1S.size());
BOOST_CHECK_EQUAL_COLLECTIONS(TmpS.begin(), TmpS.end(), R1Array, R1Array + TmpS.size());
BOOST_CHECK_EQUAL_COLLECTIONS(R2S.begin(), R2S.end(), R2Array, R2Array + R2S.size());
BOOST_CHECK_EQUAL_COLLECTIONS(ZeroS.begin(), ZeroS.end(), ZeroArray, ZeroArray + ZeroS.size());
BOOST_CHECK_EQUAL_COLLECTIONS(OneS.begin(), OneS.end(), OneArray, OneArray + OneS.size());
BOOST_CHECK_EQUAL_COLLECTIONS(R1S.begin(), R1S.end(), R1Array, R1Array + uint160::size());
BOOST_CHECK_EQUAL_COLLECTIONS(TmpS.begin(), TmpS.end(), R1Array, R1Array + uint160::size());
BOOST_CHECK_EQUAL_COLLECTIONS(R2S.begin(), R2S.end(), R2Array, R2Array + uint160::size());
BOOST_CHECK_EQUAL_COLLECTIONS(ZeroS.begin(), ZeroS.end(), ZeroArray, ZeroArray + uint160::size());
BOOST_CHECK_EQUAL_COLLECTIONS(OneS.begin(), OneS.end(), OneArray, OneArray + uint160::size());
BOOST_CHECK_EQUAL(R1S.size(), sizeof(R1S));
BOOST_CHECK_EQUAL(sizeof(R1S), 20);
BOOST_CHECK_EQUAL(R1S.size(), 20);
Expand Down Expand Up @@ -307,23 +314,23 @@ BOOST_AUTO_TEST_CASE(parse)
{
std::string s_12{"0000000000000000000000000000000000000000000000000000000000000012"};
BOOST_CHECK_EQUAL(uint256S("12\0").GetHex(), s_12);
BOOST_CHECK_EQUAL(uint256S(std::string{"12\0", 3}).GetHex(), s_12);
BOOST_CHECK_EQUAL(uint256S(std::string_view{"12\0", 3}).GetHex(), s_12);
BOOST_CHECK_EQUAL(uint256S("0x12").GetHex(), s_12);
BOOST_CHECK_EQUAL(uint256S(" 0x12").GetHex(), s_12);
BOOST_CHECK_EQUAL(uint256S(" 12").GetHex(), s_12);
}
{
std::string s_1{uint256::ONE.GetHex()};
BOOST_CHECK_EQUAL(uint256S("1\0").GetHex(), s_1);
BOOST_CHECK_EQUAL(uint256S(std::string{"1\0", 2}).GetHex(), s_1);
BOOST_CHECK_EQUAL(uint256S(std::string_view{"1\0", 2}).GetHex(), s_1);
BOOST_CHECK_EQUAL(uint256S("0x1").GetHex(), s_1);
BOOST_CHECK_EQUAL(uint256S(" 0x1").GetHex(), s_1);
BOOST_CHECK_EQUAL(uint256S(" 1").GetHex(), s_1);
}
{
std::string s_0{uint256::ZERO.GetHex()};
BOOST_CHECK_EQUAL(uint256S("\0").GetHex(), s_0);
BOOST_CHECK_EQUAL(uint256S(std::string{"\0", 1}).GetHex(), s_0);
BOOST_CHECK_EQUAL(uint256S(std::string_view{"\0", 1}).GetHex(), s_0);
BOOST_CHECK_EQUAL(uint256S("0x").GetHex(), s_0);
BOOST_CHECK_EQUAL(uint256S(" 0x").GetHex(), s_0);
BOOST_CHECK_EQUAL(uint256S(" ").GetHex(), s_0);
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2 changes: 1 addition & 1 deletion src/test/util/setup_common.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -81,7 +81,7 @@ static FastRandomContext g_insecure_rand_ctx_temp_path;

std::ostream& operator<<(std::ostream& os, const arith_uint256& num)
{
os << ArithToUint256(num).ToString();
os << num.ToString();
return os;
}

Expand Down
37 changes: 33 additions & 4 deletions src/uint256.h
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Original file line number Diff line number Diff line change
Expand Up @@ -53,17 +53,46 @@ class base_blob
std::fill(m_data.begin(), m_data.end(), 0);
}

/** Lexicographic ordering
* @note Does NOT match the ordering on the corresponding \ref
* base_uint::CompareTo, which starts comparing from the end.
*/
constexpr int Compare(const base_blob& other) const { return std::memcmp(m_data.data(), other.m_data.data(), WIDTH); }

friend constexpr bool operator==(const base_blob& a, const base_blob& b) { return a.Compare(b) == 0; }
friend constexpr bool operator!=(const base_blob& a, const base_blob& b) { return a.Compare(b) != 0; }
friend constexpr bool operator<(const base_blob& a, const base_blob& b) { return a.Compare(b) < 0; }

// Hex string representations are little-endian.
/** @name Hex representation
*
* The reverse-byte hex representation is a convenient way to view the blob
* as a number, because it is consistent with the way the base_uint class
* converts blobs to numbers.
*
* @note base_uint treats the blob as an array of bytes with the numerically
* least significant byte first and the most significant byte last. Because
* numbers are typically written with the most significant digit first and
* the least significant digit last, the reverse hex display of the blob
* corresponds to the same numeric value that base_uint interprets from the
* blob.
* @{*/
std::string GetHex() const;
/** Unlike FromHex this accepts any invalid input, thus it is fragile and deprecated */
/** Unlike FromHex this accepts any invalid input, thus it is fragile and deprecated!
*
* - Hex numbers that don't specify enough bytes to fill the internal array
* will be treated as setting the beginning of it, which corresponds to
* the least significant bytes when converted to base_uint.
*
* - Hex numbers specifying too many bytes will have the numerically most
* significant bytes (the beginning of the string) narrowed away.
*
* - An odd count of hex digits will result in the high bits of the leftmost
* byte being zero.
* "0x123" => {0x23, 0x1, 0x0, ..., 0x0}
*/
void SetHexDeprecated(std::string_view str);
std::string ToString() const;
/**@}*/

constexpr const unsigned char* data() const { return m_data.data(); }
constexpr unsigned char* data() { return m_data.data(); }
Expand Down Expand Up @@ -93,7 +122,7 @@ class base_blob

namespace detail {
/**
* Writes the hex string (treated as little-endian) into a new uintN_t object
* Writes the hex string (in reverse byte order) into a new uintN_t object
* and only returns a value iff all of the checks pass:
* - Input length is uintN_t::size()*2
* - All characters are hex
Expand Down Expand Up @@ -134,7 +163,7 @@ class uint256 : public base_blob<256> {
static const uint256 ONE;
};

/* uint256 from std::string_view, treated as little-endian.
/* uint256 from std::string_view, containing byte-reversed hex encoding.
* DEPRECATED. Unlike FromHex this accepts any invalid input, thus it is fragile and deprecated!
*/
inline uint256 uint256S(std::string_view str)
Expand Down

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