decode_base64

SFL
Version 2.11

`decode_base64`

#include "sflmime.h"
size_t
decode_base64 (const byte *source, byte *target, size_t source_size)

Synopsis

Decodes a block of Base 64 data and stores the resulting binary data in a target buffer. The target buffer must be at least 3/4 the size of the base 64 data. Returns the number of characters output into the target buffer.

Source Code - (sflmime.c)

{
    size_t
        target_size = 0;                /*  Length of target buffer          */
    int
        nb_block;                       /*  Total number of block            */
    byte
        value,                          /*  Value of Base64 byte             */
        *p_source,                      /*  Pointer in source buffer         */
        *p_target;                      /*  Pointer in target buffer         */

    ASSERT (source);
    ASSERT (target);

    if (source_size == 0)
        return (0);

    if (!tables_initialised)
        init_conversion_tables ();

    /*  Bit positions
                  | byte 1 | byte 2 | byte 3 | byte 4 |
    Encoded block  654321   654321   654321   654321  -> 4 bytes of 6 bits
                  | byte 1 | byte 2 | byte 3 |
    Decoded block  65432165 43216543 21654321         -> 3 bytes of 8 bits
    */

    nb_block    = source_size / 4;
    target_size = (size_t) nb_block * 3;
    target [target_size] = '\0';

    p_source = (byte *) source;         /*  Point to start of buffers        */
    p_target = target;

    while (nb_block--)
      {
        /*  Byte 1                                                           */
        *p_target    = char_to_base64 [(byte) *p_source++] << 2;
        value        = char_to_base64 [(byte) *p_source++];
        *p_target++ += ((value & 0x30) >> 4);

        /*  Byte 2                                                           */
        *p_target    = ((value & 0x0F) << 4);
        value        = char_to_base64 [(byte) *p_source++];
        *p_target++ += ((value & 0x3C) >> 2);

        /*  Byte 3                                                           */
        *p_target    = (value & 0x03) << 6;
        value        = char_to_base64 [(byte) *p_source++];
        *p_target++ += value;
      }
   return (target_size);
}

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