bardecode

/*

https://github.com/superwills/NibbleAndAHalf
base64.h -- Fast base64 encoding and decoding.
version 1.0.0, April 17, 2013 143a

Copyright (C) 2013 William Sherif

This software is provided 'as-is', without any express or implied
warranty.  In no event will the authors be held liable for any damages
arising from the use of this software.

Permission is granted to anyone to use this software for any purpose,
including commercial applications, and to alter it and redistribute it
freely, subject to the following restrictions:

1. The origin of this software must not be misrepresented; you must not
claim that you wrote the original software. If you use this software
in a product, an acknowledgment in the product documentation would be
appreciated but is not required.
2. Altered source versions must be plainly marked as such, and must not be
misrepresented as being the original software.
3. This notice may not be removed or altered from any source distribution.

William Sherif
will.sherif@gmail.com

YWxsIHlvdXIgYmFzZSBhcmUgYmVsb25nIHRvIHVz

*/
#ifndef BASE64_H
#define BASE64_H

#include <stdio.h>
#include <stdlib.h>

// maps A=>0,B=>1..
const static unsigned char unb64[]={
  0,   0,   0,   0,   0,   0,   0,   0,   0,   0, //10
  0,   0,   0,   0,   0,   0,   0,   0,   0,   0, //20
  0,   0,   0,   0,   0,   0,   0,   0,   0,   0, //30
  0,   0,   0,   0,   0,   0,   0,   0,   0,   0, //40
  0,   0,   0,  62,   0,   0,   0,  63,  52,  53, //50
  54,  55,  56,  57,  58,  59,  60,  61,   0,   0, //60
  0,   0,   0,   0,   0,   0,   1,   2,   3,   4, //70
  5,   6,   7,   8,   9,  10,  11,  12,  13,  14, //80
  15,  16,  17,  18,  19,  20,  21,  22,  23,  24, //90
  25,   0,   0,   0,   0,   0,   0,  26,  27,  28, //100
  29,  30,  31,  32,  33,  34,  35,  36,  37,  38, //110
  39,  40,  41,  42,  43,  44,  45,  46,  47,  48, //120
  49,  50,  51,   0,   0,   0,   0,   0,   0,   0, //130
  0,   0,   0,   0,   0,   0,   0,   0,   0,   0, //140
  0,   0,   0,   0,   0,   0,   0,   0,   0,   0, //150
  0,   0,   0,   0,   0,   0,   0,   0,   0,   0, //160
  0,   0,   0,   0,   0,   0,   0,   0,   0,   0, //170
  0,   0,   0,   0,   0,   0,   0,   0,   0,   0, //180
  0,   0,   0,   0,   0,   0,   0,   0,   0,   0, //190
  0,   0,   0,   0,   0,   0,   0,   0,   0,   0, //200
  0,   0,   0,   0,   0,   0,   0,   0,   0,   0, //210
  0,   0,   0,   0,   0,   0,   0,   0,   0,   0, //220
  0,   0,   0,   0,   0,   0,   0,   0,   0,   0, //230
  0,   0,   0,   0,   0,   0,   0,   0,   0,   0, //240
  0,   0,   0,   0,   0,   0,   0,   0,   0,   0, //250
  0,   0,   0,   0,   0,   0,
}; // This array has 256 elements

// Converts base64 characters of length=len to binary data.
// Length of the resultant string is stored in flen
// (you must pass pointer flen).
unsigned char* unbase64( const char* ascii, int len, int *flen ) {
  const unsigned char *safeAsciiPtr = (const unsigned char*)ascii ;
  unsigned char *bin ;
  int cb=0;
  int charNo;
  int pad = 0 ;

  if( len < 2 ) { // 2 accesses below would be OOB.
    // catch empty string, return NULL as result.
    *flen=0;
    return 0;
  }
  if( safeAsciiPtr[ len-1 ]=='=' )  ++pad ;
  if( safeAsciiPtr[ len-2 ]=='=' )  ++pad ;

  *flen = 3*len/4 - pad ;
  bin = (unsigned char*)malloc( *flen ) ;
  if( !bin )
  {
    puts( "ERROR: unbase64 could not allocate enough memory." ) ;
    *flen=0;
    return 0;
  }

  for( charNo=0; charNo <= len - 4 - pad ; charNo+=4 )
  {
    int A=unb64[safeAsciiPtr[charNo]];
    int B=unb64[safeAsciiPtr[charNo+1]];
    int C=unb64[safeAsciiPtr[charNo+2]];
    int D=unb64[safeAsciiPtr[charNo+3]];

    bin[cb++] = (A<<2) | (B>>4) ;
    bin[cb++] = (B<<4) | (C>>2) ;
    bin[cb++] = (C<<6) | (D) ;
  }

  if( pad==1 )
  {
    int A=unb64[safeAsciiPtr[charNo]];
    int B=unb64[safeAsciiPtr[charNo+1]];
    int C=unb64[safeAsciiPtr[charNo+2]];

    bin[cb++] = (A<<2) | (B>>4) ;
    bin[cb++] = (B<<4) | (C>>2) ;
  }
  else if( pad==2 )
  {
    int A=unb64[safeAsciiPtr[charNo]];
    int B=unb64[safeAsciiPtr[charNo+1]];

    bin[cb++] = (A<<2) | (B>>4) ;
  }

  return bin ;
}

#endif