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#include "base64bufbase.ih"
#include <iostream>
bool Base64BufBase::decrypt()
{
// reading blocks of 4 characters.
// If the first byte is \n then reread it (from the next line).
// Stop if the first character is not in the set of accepted base64
// characters
while (true)
{
int b0 = d_in.get(); // first of 4
if (b0 == '\n') // is a \n: read the next
b0 = d_in.get(); // returns 0xff on failure
if (s_tabStr.find(b0) == string::npos) // b0 is not in the set of
{ // base64 chars
d_in.unget();
return false; // signal 'done'
}
int b1 = d_in.get(); // continue: there must be
int b2 = d_in.get(); // at least 4 characters
int b3 = d_in.get();
b0 = indexOf(b0); // convert chars to indices:
b1 = indexOf(b1); // their bit patterns are
// stored in max, 3 decrypted
// characters
d_buffer.push_back(
(b0 << 2) // 6 bits of b0 become bits 2..7
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bits<4, 2>(b1) // bits 4,5 of b1 become bits 0..1
);
if (b2 == '=') // encountered '==': only one output char
return false;
b2 = indexOf(b2);
d_buffer.push_back(
bits<0, 4, 4>(b1) // bits 0..3 become bits 4..7
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bits<2, 4>(b2) // bits 2..5 become bits 0..3
);
if (b3 == '=') // encountered '==': two output chars
return false;
d_buffer.push_back(
bits<0, 2, 6>(b2) // bits 0..1 become bits 6..7
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indexOf(b3) // all 6 bits of b3
);
if (d_buffer.size() > 100) // flush if the buffer is full
return true;
}
}
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