Character Lower-casing: Locale-aware vs Lookup Table

Question 18 / 51 • Correct so far: 0 (0 answered)

Snippet A

Locale Lower

std::string lowerCase(const std::string& s) {
    std::locale loc;
    std::string out(s.size(), '\0');
    for (std::size_t i = 0; i < s.size(); ++i)
        out[i] = std::tolower(s[i], loc);
    return out;
}

std::string result = lowerCase(SAMPLE);
Snippet B

Table Lower

std::string lowerCase(const std::string& s) {
    std::string out(s.size(), '\0');
    for (std::size_t i = 0; i < s.size(); ++i)
        out[i] = static_cast<char>(LOWER_TABLE[static_cast<unsigned char>(s[i])]);
    return out;
}

std::string result = lowerCase(SAMPLE);
Shared test data (shared-setup) 
static const std::string SAMPLE = []() {
    std::string s;
    s.reserve(4096);
    for (int i = 0; i < 4096; ++i)
        s += static_cast<char>('A' + (i % 26));
    return s;
}();

static const std::array<unsigned char, 256> LOWER_TABLE = []() {
    std::array<unsigned char, 256> t;
    for (int i = 0; i < 256; ++i)
        t[i] = static_cast<unsigned char>(std::tolower(i));
    return t;
}();

Which snippet is faster?

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