base64.cpp

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#include "./arduino_base64.h"
 
namespace {
    constexpr char CODE[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
 
    uint8_t indexOf(char search) {
        for(uint8_t i = 0; i < 64; i++) {
            if(::CODE[i] == search) {
                return i;
            }
        }
 
        return 0xFF;
    }
 
    void to6x4(uint8_t* input, uint8_t* output) {
        output[0] = (input[0] & 0xFC) >> 2;
        output[1] = ((input[0] & 0x03) << 4) + ((input[1] & 0xF0) >> 4);
        output[2] = ((input[1] & 0x0F) << 2) + ((input[2] & 0xC0) >> 6);
        output[3] = input[2] & 0x3F;
    }
 
    void to8x3(uint8_t* input, uint8_t* output) {
        output[0] = (input[0] << 2) + ((input[1] & 0x30) >> 4);
        output[1] = ((input[1] & 0x0F) << 4) + ((input[2] & 0x3C) >> 2);
        output[2] = ((input[2] & 0x03) << 6) + input[3];
    }
}
 
void base64::encode(const uint8_t* input, size_t inputLength, char* output) {
    uint8_t position = 0;
    uint8_t bit8x3[3] = {};
    uint8_t bit6x4[4] = {};
 
    while(inputLength--) {
        bit8x3[position++] = *input++;
 
        if(position == 3) {
            ::to6x4(bit8x3, bit6x4);
 
            for(const auto &v: bit6x4) {
                *output++ = ::CODE[v];
            }
 
            position = 0;
        }
    }
 
    if(position) {
        for(uint8_t i = position; i < 3; i++) {
            bit8x3[i] = 0x00;
        }
 
        ::to6x4(bit8x3, bit6x4);
 
        for(uint8_t i = 0; i < position + 1; i++) {
            *output++ = ::CODE[bit6x4[i]];
        }
 
        while(position++ < 3) {
            *output++ = '=';
        }
    }
 
    *output = '\0';
}
 
size_t base64::encodeLength(size_t inputLength) {
    return (inputLength + 2 - ((inputLength + 2) % 3)) / 3 * 4 + 1;
}
 
void base64::decode(const char* input, size_t inputLength, uint8_t* output) {
    uint8_t position = 0;
    uint8_t bit8x3[3] = {};
    uint8_t bit6x4[4] = {};
 
    while(inputLength--) {
        if(*input == '=') {
            break;
        }
 
        bit6x4[position++] = ::indexOf(*input++);
 
        if(position == 4) {
            ::to8x3(bit6x4, bit8x3);
 
            for(const auto &v: bit8x3) {
                *output++ = v;
            }
 
            position = 0;
        }
    }
 
    if(position) {
        for(uint8_t i = position; i < 4; i++) {
            bit6x4[i] = 0x00;
        }
 
        ::to8x3(bit6x4, bit8x3);
 
        for(uint8_t i = 0; i < position - 1; i++) {
            *output++ = bit8x3[i];
        }
    }
}
 
size_t base64::decodeLength(const char* input) {
    auto inputLength = strlen(input);
    uint8_t equal = 0;
 
    input += inputLength - 1;
 
    while(*input-- == '=') {
        equal++;
    }
 
    return 6 * inputLength / 8 - equal;
}