/** <https://github.com/miloyip/itoa-benchmark/blob/940542a7770155ee3e9f2777ebc178dc899b43e0/src/branchlut.cpp>
 */

#include <string.h>
#include <stdint.h>

static const char gDigitsLut[200] = {
    '0','0','0','1','0','2','0','3','0','4','0','5','0','6','0','7','0','8','0','9',
    '1','0','1','1','1','2','1','3','1','4','1','5','1','6','1','7','1','8','1','9',
    '2','0','2','1','2','2','2','3','2','4','2','5','2','6','2','7','2','8','2','9',
    '3','0','3','1','3','2','3','3','3','4','3','5','3','6','3','7','3','8','3','9',
    '4','0','4','1','4','2','4','3','4','4','4','5','4','6','4','7','4','8','4','9',
    '5','0','5','1','5','2','5','3','5','4','5','5','5','6','5','7','5','8','5','9',
    '6','0','6','1','6','2','6','3','6','4','6','5','6','6','6','7','6','8','6','9',
    '7','0','7','1','7','2','7','3','7','4','7','5','7','6','7','7','7','8','7','9',
    '8','0','8','1','8','2','8','3','8','4','8','5','8','6','8','7','8','8','8','9',
    '9','0','9','1','9','2','9','3','9','4','9','5','9','6','9','7','9','8','9','9'
};

// Branching for different cases (forward)
// Use lookup table of two digits

size_t u32toa_branchlut(uint32_t value, char* buffer) {
    char* start = buffer;

    if (value < 10000) {
        const uint32_t d1 = (value / 100) << 1;
        const uint32_t d2 = (value % 100) << 1;
        
        if (value >= 1000)
            *buffer++ = gDigitsLut[d1];
        if (value >= 100)
            *buffer++ = gDigitsLut[d1 + 1];
        if (value >= 10)
            *buffer++ = gDigitsLut[d2];
        *buffer++ = gDigitsLut[d2 + 1];
    }
    else if (value < 100000000) {
        // value = bbbbcccc
        const uint32_t b = value / 10000;
        const uint32_t c = value % 10000;
        
        const uint32_t d1 = (b / 100) << 1;
        const uint32_t d2 = (b % 100) << 1;
        
        const uint32_t d3 = (c / 100) << 1;
        const uint32_t d4 = (c % 100) << 1;
        
        if (value >= 10000000)
            *buffer++ = gDigitsLut[d1];
        if (value >= 1000000)
            *buffer++ = gDigitsLut[d1 + 1];
        if (value >= 100000)
            *buffer++ = gDigitsLut[d2];
        *buffer++ = gDigitsLut[d2 + 1];
        
        *buffer++ = gDigitsLut[d3];
        *buffer++ = gDigitsLut[d3 + 1];
        *buffer++ = gDigitsLut[d4];
        *buffer++ = gDigitsLut[d4 + 1];
    }
    else {
        // value = aabbbbcccc in decimal
        
        const uint32_t a = value / 100000000; // 1 to 42
        value %= 100000000;
        
        if (a >= 10) {
            const unsigned i = a << 1;
            *buffer++ = gDigitsLut[i];
            *buffer++ = gDigitsLut[i + 1];
        }
        else
            *buffer++ = '0' + static_cast<char>(a);

        const uint32_t b = value / 10000; // 0 to 9999
        const uint32_t c = value % 10000; // 0 to 9999
        
        const uint32_t d1 = (b / 100) << 1;
        const uint32_t d2 = (b % 100) << 1;
        
        const uint32_t d3 = (c / 100) << 1;
        const uint32_t d4 = (c % 100) << 1;
        
        *buffer++ = gDigitsLut[d1];
        *buffer++ = gDigitsLut[d1 + 1];
        *buffer++ = gDigitsLut[d2];
        *buffer++ = gDigitsLut[d2 + 1];
        *buffer++ = gDigitsLut[d3];
        *buffer++ = gDigitsLut[d3 + 1];
        *buffer++ = gDigitsLut[d4];
        *buffer++ = gDigitsLut[d4 + 1];
    }
    return buffer - start;
}

size_t i32toa_branchlut(int32_t value, char* buffer) {
    size_t length = 0;
    if (value < 0) {
        ++length;
        *buffer++ = '-';
        value = -value;
    }

    return length + u32toa_branchlut(static_cast<uint32_t>(value), buffer);
}

size_t u64toa_branchlut(uint64_t value, char* buffer) {
    char* start = buffer;
    if (value < 100000000) {
        uint32_t v = static_cast<uint32_t>(value);
        if (v < 10000) {
            const uint32_t d1 = (v / 100) << 1;
            const uint32_t d2 = (v % 100) << 1;
            
            if (v >= 1000)
                *buffer++ = gDigitsLut[d1];
            if (v >= 100)
                *buffer++ = gDigitsLut[d1 + 1];
            if (v >= 10)
                *buffer++ = gDigitsLut[d2];
            *buffer++ = gDigitsLut[d2 + 1];
        }
        else {
            // value = bbbbcccc
            const uint32_t b = v / 10000;
            const uint32_t c = v % 10000;
            
            const uint32_t d1 = (b / 100) << 1;
            const uint32_t d2 = (b % 100) << 1;
            
            const uint32_t d3 = (c / 100) << 1;
            const uint32_t d4 = (c % 100) << 1;
            
            if (value >= 10000000)
                *buffer++ = gDigitsLut[d1];
            if (value >= 1000000)
                *buffer++ = gDigitsLut[d1 + 1];
            if (value >= 100000)
                *buffer++ = gDigitsLut[d2];
            *buffer++ = gDigitsLut[d2 + 1];
            
            *buffer++ = gDigitsLut[d3];
            *buffer++ = gDigitsLut[d3 + 1];
            *buffer++ = gDigitsLut[d4];
            *buffer++ = gDigitsLut[d4 + 1];
        }
    }
    else if (value < 10000000000000000) {
        const uint32_t v0 = static_cast<uint32_t>(value / 100000000);
        const uint32_t v1 = static_cast<uint32_t>(value % 100000000);
        
        const uint32_t b0 = v0 / 10000;
        const uint32_t c0 = v0 % 10000;
        
        const uint32_t d1 = (b0 / 100) << 1;
        const uint32_t d2 = (b0 % 100) << 1;
        
        const uint32_t d3 = (c0 / 100) << 1;
        const uint32_t d4 = (c0 % 100) << 1;

        const uint32_t b1 = v1 / 10000;
        const uint32_t c1 = v1 % 10000;
        
        const uint32_t d5 = (b1 / 100) << 1;
        const uint32_t d6 = (b1 % 100) << 1;
        
        const uint32_t d7 = (c1 / 100) << 1;
        const uint32_t d8 = (c1 % 100) << 1;

        if (value >= 1000000000000000)
            *buffer++ = gDigitsLut[d1];
        if (value >= 100000000000000)
            *buffer++ = gDigitsLut[d1 + 1];
        if (value >= 10000000000000)
            *buffer++ = gDigitsLut[d2];
        if (value >= 1000000000000)
            *buffer++ = gDigitsLut[d2 + 1];
        if (value >= 100000000000)
            *buffer++ = gDigitsLut[d3];
        if (value >= 10000000000)
            *buffer++ = gDigitsLut[d3 + 1];
        if (value >= 1000000000)
            *buffer++ = gDigitsLut[d4];
        if (value >= 100000000)
            *buffer++ = gDigitsLut[d4 + 1];
        
        *buffer++ = gDigitsLut[d5];
        *buffer++ = gDigitsLut[d5 + 1];
        *buffer++ = gDigitsLut[d6];
        *buffer++ = gDigitsLut[d6 + 1];
        *buffer++ = gDigitsLut[d7];
        *buffer++ = gDigitsLut[d7 + 1];
        *buffer++ = gDigitsLut[d8];
        *buffer++ = gDigitsLut[d8 + 1];
    }
    else {
        const uint32_t a = static_cast<uint32_t>(value / 10000000000000000); // 1 to 1844
        value %= 10000000000000000;
        
        if (a < 10)
            *buffer++ = '0' + static_cast<char>(a);
        else if (a < 100) {
            const uint32_t i = a << 1;
            *buffer++ = gDigitsLut[i];
            *buffer++ = gDigitsLut[i + 1];
        }
        else if (a < 1000) {
            *buffer++ = '0' + static_cast<char>(a / 100);
            
            const uint32_t i = (a % 100) << 1;
            *buffer++ = gDigitsLut[i];
            *buffer++ = gDigitsLut[i + 1];
        }
        else {
            const uint32_t i = (a / 100) << 1;
            const uint32_t j = (a % 100) << 1;
            *buffer++ = gDigitsLut[i];
            *buffer++ = gDigitsLut[i + 1];
            *buffer++ = gDigitsLut[j];
            *buffer++ = gDigitsLut[j + 1];
        }
        
        const uint32_t v0 = static_cast<uint32_t>(value / 100000000);
        const uint32_t v1 = static_cast<uint32_t>(value % 100000000);
        
        const uint32_t b0 = v0 / 10000;
        const uint32_t c0 = v0 % 10000;
        
        const uint32_t d1 = (b0 / 100) << 1;
        const uint32_t d2 = (b0 % 100) << 1;
        
        const uint32_t d3 = (c0 / 100) << 1;
        const uint32_t d4 = (c0 % 100) << 1;
        
        const uint32_t b1 = v1 / 10000;
        const uint32_t c1 = v1 % 10000;
        
        const uint32_t d5 = (b1 / 100) << 1;
        const uint32_t d6 = (b1 % 100) << 1;
        
        const uint32_t d7 = (c1 / 100) << 1;
        const uint32_t d8 = (c1 % 100) << 1;
        
        *buffer++ = gDigitsLut[d1];
        *buffer++ = gDigitsLut[d1 + 1];
        *buffer++ = gDigitsLut[d2];
        *buffer++ = gDigitsLut[d2 + 1];
        *buffer++ = gDigitsLut[d3];
        *buffer++ = gDigitsLut[d3 + 1];
        *buffer++ = gDigitsLut[d4];
        *buffer++ = gDigitsLut[d4 + 1];
        *buffer++ = gDigitsLut[d5];
        *buffer++ = gDigitsLut[d5 + 1];
        *buffer++ = gDigitsLut[d6];
        *buffer++ = gDigitsLut[d6 + 1];
        *buffer++ = gDigitsLut[d7];
        *buffer++ = gDigitsLut[d7 + 1];
        *buffer++ = gDigitsLut[d8];
        *buffer++ = gDigitsLut[d8 + 1];
    }
    
    return buffer - start;
}

size_t i64toa_branchlut(int64_t value, char* buffer) {
    size_t length = 0;
    if (value < 0) {
        ++length;
        *buffer++ = '-';
        value = -value;
    }

    return length + u64toa_branchlut(static_cast<uint64_t>(value), buffer);
}
