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Use a lookup table for decoding #1

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Aug 12, 2023
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Use a lookup table for decoding #1

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30 changes: 22 additions & 8 deletions base64.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -41,7 +41,7 @@
// two sets of base64 characters needs to be chosen.
// They differ in their last two characters.
//
static const char* base64_chars[2] = {
static const char* to_base64_chars[2] = {
"ABCDEFGHIJKLMNOPQRSTUVWXYZ"
"abcdefghijklmnopqrstuvwxyz"
"0123456789"
Expand All @@ -52,17 +52,31 @@ static const char* base64_chars[2] = {
"0123456789"
"-_"};

static const unsigned char from_base64_chars[256] = {
64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 62, 64, 62, 64, 63,
52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 64, 64, 64, 64, 64, 64,
64, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,
15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 64, 64, 64, 64, 63,
64, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,
41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 64, 64, 64, 64, 64,
64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64
};

static unsigned int pos_of_char(const unsigned char chr) {
//
// Return the position of chr within base64_encode()
//

if (chr >= 'A' && chr <= 'Z') return chr - 'A';
else if (chr >= 'a' && chr <= 'z') return chr - 'a' + ('Z' - 'A') + 1;
else if (chr >= '0' && chr <= '9') return chr - '0' + ('Z' - 'A') + ('z' - 'a') + 2;
else if (chr == '+' || chr == '-') return 62; // Be liberal with input and accept both url ('-') and non-url ('+') base 64 characters (
else if (chr == '/' || chr == '_') return 63; // Ditto for '/' and '_'
else
if (from_base64_chars[chr] != 64) return from_base64_chars[chr];
//
// 2020-10-23: Throw std::exception rather than const char*
//(Pablo Martin-Gomez, https://github.com/Bouska)
Expand Down Expand Up @@ -123,7 +137,7 @@ std::string base64_encode(unsigned char const* bytes_to_encode, size_t in_len, b
// the correct character set is chosen by subscripting
// base64_chars with url.
//
const char* base64_chars_ = base64_chars[url];
const char* base64_chars_ = to_base64_chars[url];

std::string ret;
ret.reserve(len_encoded);
Expand Down