/*
cdecoder.c - c source to a base64 decoding algorithm implementation

This is part of the libb64 project, and has been placed in the public domain.
For details, see http://sourceforge.net/projects/libb64
*/

#include "cdecode.h"

int base64_decode_value(char value_in){
    static const char decoding[] = {62,-1,-1,-1,63,52,53,54,55,56,57,58,59,60,61,-1,-1,-1,-2,-1,-1,-1,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,-1,-1,-1,-1,-1,-1,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51};
    static const char decoding_size = sizeof(decoding);
    value_in -= 43;
    if ((signed char)value_in < 0 || value_in > decoding_size) return -1;
    return decoding[(int)value_in];
}

void base64_init_decodestate(base64_decodestate* state_in){
    state_in->step = step_a;
    state_in->plainchar = 0;
}

size_t base64_decode_block(const char* code_in, const size_t length_in, char* plaintext_out, base64_decodestate* state_in){
    const char* codechar = code_in;
    char* plainchar = plaintext_out;
    char fragment;
    
    *plainchar = state_in->plainchar;
    
    switch (state_in->step){
        while (1){
            case step_a:
                do{
                    if (codechar == code_in+length_in){
                        state_in->step = step_a;
                        state_in->plainchar = *plainchar;
                        return plainchar - plaintext_out;
                    }
                    fragment = (char)base64_decode_value(*codechar++);
                } while ((signed char)fragment < 0);
                *plainchar = (fragment & 0x03f) << 2;

            case step_b:
                do{
                    if (codechar == code_in+length_in){
                        state_in->step = step_b;
                        state_in->plainchar = *plainchar;
                        return plainchar - plaintext_out;
                    }
                    fragment = (char)base64_decode_value(*codechar++);
                } while ((signed char)fragment < 0);
                *plainchar++ |= (fragment & 0x030) >> 4;
                *plainchar    = (fragment & 0x00f) << 4;
            case step_c:
                do{
                    if (codechar == code_in+length_in)
                    {
                        state_in->step = step_c;
                        state_in->plainchar = *plainchar;
                        return plainchar - plaintext_out;
                    }
                    fragment = (char)base64_decode_value(*codechar++);
                } while ((signed char)fragment < 0);
                *plainchar++ |= (fragment & 0x03c) >> 2;
                *plainchar    = (fragment & 0x003) << 6;
            case step_d:
                do{
                    if (codechar == code_in+length_in){
                        state_in->step = step_d;
                        state_in->plainchar = *plainchar;
                        return plainchar - plaintext_out;
                    }
                    fragment = (char)base64_decode_value(*codechar++);
                } while ((signed char)fragment < 0);
                *plainchar++   |= (fragment & 0x03f);
        }
    }
    /* control should not reach here */
    return plainchar - plaintext_out;
}