Repository: bitcoin/bitcoin
File: src/uint256.cpp (C++)

Code before:
        m_data_rev[i] = m_data[WIDTH - 1 - i];
    }
    return HexStr(m_data_rev);
}

template <unsigned int BITS>
void base_blob<BITS>::SetHex(const char* psz)
{
    std::fill(m_data.begin(), m_data.end(), 0);

    // skip leading spaces
    while (IsSpace(*psz))
        psz++;

    // skip 0x
    if (psz[0] == '0' && ToLower(psz[1]) == 'x')
        psz += 2;

    // hex string to uint
    size_t digits = 0;
    while (::HexDigit(psz[digits]) != -1)
        digits++;
    unsigned char* p1 = m_data.data();
    unsigned char* pend = p1 + WIDTH;
    while (digits > 0 && p1 < pend) {
        *p1 = ::HexDigit(psz[--digits]);
        if (digits > 0) {
            *p1 |= ((unsigned char)::HexDigit(psz[--digits]) << 4);
            p1++;
        }
    }
}

template <unsigned int BITS>
void base_blob<BITS>::SetHex(const std::string& str)
{
    SetHex(str.c_str());
}

template <unsigned int BITS>
std::string base_blob<BITS>::ToString() const
{
    return (GetHex());
}

// Explicit instantiations for base_blob<160>
template std::string base_blob<160>::GetHex() const;
template std::string base_blob<160>::ToString() const;
template void base_blob<160>::SetHex(const char*);
template void base_blob<160>::SetHex(const std::string&);


Review comment (suggestion):
I see this uses little-endian encoding, while e.g. `TryParseHex` uses big-endian, right?
Do you happen to know what the reason is? Should we maybe document this?
Do we need to keep the endianness in every scenario (since that's why we need the digit counting at the beginning) or could we use big-endian in any of the usages, e.g. if these hex strings aren't persisted or someting (in a different PR, of course)?

See: https://github.com/bitcoin/bitcoin/pull/30482/commits/f77d961d926405637dfbdfb9a9baea1fab4f1b7b#r1685489845

Code after:
        m_data_rev[i] = m_data[WIDTH - 1 - i];
    }
    return HexStr(m_data_rev);
}

template <unsigned int BITS>
void base_blob<BITS>::SetHex(const std::string_view str)
{
    std::fill(m_data.begin(), m_data.end(), 0);

    const auto trimmed = util::RemovePrefixView(util::TrimStringView(str), "0x");

    // Note: if we are passed a greater number of digits than would fit as bytes
    // in m_data, we will be discarding the leftmost ones.
    // str="12bc" in a WIDTH=1 m_data => m_data[] == "\0xbc", not "0x12".
    size_t digits = 0;
    for (const char c : trimmed) {
        if (::HexDigit(c) == -1) break;
        ++digits;
    }
    unsigned char* p1 = m_data.data();
    unsigned char* pend = p1 + WIDTH;
    while (digits > 0 && p1 < pend) {
        *p1 = ::HexDigit(trimmed[--digits]);
        if (digits > 0) {
            *p1 |= ((unsigned char)::HexDigit(trimmed[--digits]) << 4);
            p1++;
        }
    }
}

template <unsigned int BITS>
std::string base_blob<BITS>::ToString() const
{
    return (GetHex());
}

// Explicit instantiations for base_blob<160>
template std::string base_blob<160>::GetHex() const;
template std::string base_blob<160>::ToString() const;
template void base_blob<160>::SetHex(std::string_view);

// Explicit instantiations for base_blob<256>
template std::string base_blob<256>::GetHex() const;
template std::string base_blob<256>::ToString() const;
template void base_blob<256>::SetHex(std::string_view);

const uint256 uint256::ZERO(0);
const uint256 uint256::ONE(1);