cencode.c

/*
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 "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;
      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;
      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;
}