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  1. #include <stdlib.h>
  2. #include <stdio.h>
  3. #include <string.h>
  4.  
  5.  
  6. static const unsigned char pr2six[256] =
  7. {
  8.     64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
  9.     64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
  10.     64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 62, 64, 64, 64, 63,
  11.     52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 64, 64, 64, 64, 64, 64,
  12.     64,  0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14,
  13.     15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 64, 64, 64, 64, 64,
  14.     64, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,
  15.     41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 64, 64, 64, 64, 64,
  16.     64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
  17.     64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
  18.     64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
  19.     64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
  20.     64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
  21.     64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
  22.     64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
  23.     64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64
  24. };
  25.  
  26.  
  27. int Base64decode( char * bufplain, const char * bufcoded )
  28. {
  29.     int nbytesdecoded;
  30.     register const unsigned char *bufin;
  31.     register unsigned char *bufout;
  32.     register int nprbytes;
  33.  
  34.     bufin = (const unsigned char *) bufcoded;
  35.     while (pr2six[*(bufin++)] <= 63);
  36.     nprbytes = (bufin - (const unsigned char *) bufcoded) - 1;
  37.     nbytesdecoded = ((nprbytes + 3) / 4) * 3;
  38.  
  39.     bufout = (unsigned char *) bufplain;
  40.     bufin = (const unsigned char *) bufcoded;
  41.  
  42.     while (nprbytes > 4)
  43.     {
  44.         *(bufout++) = (unsigned char) (pr2six[*bufin] << 2 | pr2six[bufin[1]] >> 4);
  45.         *(bufout++) = (unsigned char) (pr2six[bufin[1]] << 4 | pr2six[bufin[2]] >> 2);
  46.         *(bufout++) = (unsigned char) (pr2six[bufin[2]] << 6 | pr2six[bufin[3]]);
  47.         bufin += 4;
  48.         nprbytes -= 4;
  49.     }
  50.  
  51.     if (nprbytes > 1)
  52.     {
  53.         *(bufout++) = (unsigned char) (pr2six[*bufin] << 2 | pr2six[bufin[1]] >> 4);
  54.     }
  55.  
  56.     if (nprbytes > 2)
  57.     {
  58.         *(bufout++) = (unsigned char) (pr2six[bufin[1]] << 4 | pr2six[bufin[2]] >> 2);
  59.     }
  60.  
  61.     if (nprbytes > 3)
  62.     {
  63.         *(bufout++) = (unsigned char) (pr2six[bufin[2]] << 6 | pr2six[bufin[3]]);
  64.     }
  65.  
  66.     *(bufout++) = '\0';
  67.     nbytesdecoded -= (4 - nprbytes) & 3;
  68.  
  69.     return nbytesdecoded;
  70. }
  71.  
  72.  
  73. int main( void )
  74. {
  75.     char * encoded = "eyJtZXNzYWdlIjoxLCJhZGQiOjEsInZhbHVlIjoiMSJ9";
  76.     char decoded[ 100 ] = {0};
  77.  
  78.     Base64decode( decoded, encoded );
  79.  
  80.     printf("String codificada  : %s\n", encoded );
  81.     printf("String decodificada: %s\n", decoded );
  82.  
  83.     return 0;
  84. }
  85.  
  86. /* fim-de-arquivo */
Success #stdin #stdout 0s 2168KB
comments (?)
stdin
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Standard input is empty
stdout
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String codificada  : eyJtZXNzYWdlIjoxLCJhZGQiOjEsInZhbHVlIjoiMSJ9
String decodificada: {"message":1,"add":1,"value":"1"}
https://ideone.com/HanXNA
language:
C (gcc 8.3)
created:
7 years ago
visibility:
public

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