base64.cpp

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#include "pfc.h"

namespace bitWriter {
    static void set_bit(t_uint8 * p_stream,size_t p_offset, bool state) {
        t_uint8 mask = 1 << (7-(p_offset&7));
        t_uint8 & byte = p_stream[p_offset>>3];
        byte = (byte & ~mask) | (state ? mask : 0);
    }
    static void set_bits(t_uint8 * stream, t_size offset, t_size word, t_size bits) {
        for(t_size walk = 0; walk < bits; ++walk) {
            t_uint8 bit = (t_uint8)((word >> (bits - walk - 1))&1);
            set_bit(stream, offset+walk, bit != 0);
        }
    }
};

namespace pfc {
    t_size base64_decode_estimate(const char * text) {
        t_size textLen = strlen(text);
        if (textLen % 4 != 0) throw pfc::exception_invalid_params();
        t_size outLen = (textLen / 4) * 3;
        
        if (textLen >= 4) {
            if (text[textLen-1] == '=') {
                textLen--; outLen--;
                if (text[textLen-1] == '=') {
                    textLen--; outLen--;
                }
            }
        }
        return outLen;
    }

    

    void base64_decode(const char * text, void * out) {
        static const char alphabet[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
        t_uint8 alphabetRev[256];
        for(t_size walk = 0; walk < PFC_TABSIZE(alphabetRev); ++walk) alphabetRev[walk] = 0xFF;
        for(t_size walk = 0; walk < PFC_TABSIZE(alphabet); ++walk) alphabetRev[ (unsigned) alphabet[walk]] = (t_uint8)walk;
        const t_size textLen = strlen(text);

        if (textLen % 4 != 0) throw pfc::exception_invalid_params();
        if (textLen == 0) return;
        
        t_size outWritePtr = 0;

        {
            const t_size max = textLen - 4;
            t_size textWalk = 0;
            for(; textWalk < max; textWalk ++) {
                const t_uint8 v = alphabetRev[(t_uint8)text[textWalk]];
                if (v == 0xFF) throw pfc::exception_invalid_params();
                bitWriter::set_bits(reinterpret_cast<t_uint8*>(out),outWritePtr,v,6);
                outWritePtr += 6;
            }

            t_uint8 temp[3];
            t_size tempWritePtr = 0;
            for(; textWalk < textLen; textWalk ++) {
                const char c = text[textWalk];
                if (c == '=') break;
                const t_uint8 v = alphabetRev[(t_uint8)c];
                if (v == 0xFF) throw pfc::exception_invalid_params();
                bitWriter::set_bits(temp,tempWritePtr,v,6);
                tempWritePtr += 6;
            }
            for(; textWalk < textLen; textWalk ++) {
                if (text[textWalk] != '=') throw pfc::exception_invalid_params();
            }
            memcpy(reinterpret_cast<t_uint8*>(out) + (outWritePtr/8), temp, tempWritePtr/8);
        }
    }
    void base64_encode(pfc::string_base & out, const void * in, t_size inSize) {
        out.reset(); base64_encode_append(out, in, inSize);
    }
    void base64_encode_append(pfc::string_base & out, const void * in, t_size inSize) {
        static const char alphabet[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
        int shift = 0;
        int accum = 0;
        const t_uint8 * inPtr = reinterpret_cast<const t_uint8*>(in);

        for(t_size walk = 0; walk < inSize; ++walk) {
            accum <<= 8;
            shift += 8;
            accum |= inPtr[walk];
            while ( shift >= 6 ) {
                shift -= 6;
                out << format_char( alphabet[(accum >> shift) & 0x3F] );
            }
        }
        if (shift == 4) {
            out << format_char( alphabet[(accum & 0xF)<<2] ) << "=";
        } else if (shift == 2) {
            out << format_char( alphabet[(accum & 0x3)<<4] ) << "==";
        }
    }

}