cencode.c

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/*
cencoder.c - c source to a base64 encoding 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 <b64/cencode.h>

const int CHARS_PER_LINE = 72;

void base64_init_encodestate(base64_encodestate* state_in)
{
        state_in->step = step_A;
        state_in->result = 0;
        state_in->stepcount = 0;
}

char base64_encode_value(char value_in)
{
        static const char* encoding = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
        if (value_in > 63) return '=';
        return encoding[(int)value_in];
}

int base64_encode_block(const char* plaintext_in, int length_in, char* code_out, base64_encodestate* state_in)
{
        const char* plainchar = plaintext_in;
        const char* const plaintextend = plaintext_in + length_in;
        char* codechar = code_out;
        char result;
        char fragment;
        
        result = state_in->result;
        
        switch (state_in->step)
        {
                while (1)
                {
        case step_A:
                        if (plainchar == plaintextend)
                        {
                                state_in->result = result;
                                state_in->step = step_A;
                                return codechar - code_out;
                        }
                        fragment = *plainchar++;
                        result = (fragment & 0x0fc) >> 2;
                        *codechar++ = base64_encode_value(result);
                        result = (fragment & 0x003) << 4;
                        //lint -fallthrough
        case step_B:
                        if (plainchar == plaintextend)
                        {
                                state_in->result = result;
                                state_in->step = step_B;
                                return codechar - code_out;
                        }
                        fragment = *plainchar++;
                        result |= (fragment & 0x0f0) >> 4;
                        *codechar++ = base64_encode_value(result);
                        result = (fragment & 0x00f) << 2;
                        //lint -fallthrough
        case step_C:
                        if (plainchar == plaintextend)
                        {
                                state_in->result = result;
                                state_in->step = step_C;
                                return codechar - code_out;
                        }
                        fragment = *plainchar++;
                        result |= (fragment & 0x0c0) >> 6;
                        *codechar++ = base64_encode_value(result);
                        result  = (fragment & 0x03f) >> 0;
                        *codechar++ = base64_encode_value(result);
                        
                        ++(state_in->stepcount);
                        if (state_in->stepcount == CHARS_PER_LINE/4)
                        {
                                *codechar++ = '\n';
                                state_in->stepcount = 0;
                        }
                }
        }
        /* control should not reach here */
        return codechar - code_out;
}

int base64_encode_blockend(char* code_out, base64_encodestate* state_in)
{
        char* codechar = code_out;
        
        switch (state_in->step)
        {
        case step_B:
                *codechar++ = base64_encode_value(state_in->result);
                *codechar++ = '=';
                *codechar++ = '=';
                break;
        case step_C:
                *codechar++ = base64_encode_value(state_in->result);
                *codechar++ = '=';
                break;
        case step_A:
                break;
        }
        *codechar++ = '\n';
        
        return codechar - code_out;
}