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Base64 Encode Decode in ALGOL 60
Published on 10 April 2026 (Updated: 10 April 2026)
Welcome to the Base64 Encode Decode in ALGOL 60 page! Here, you'll find the source code for this program as well as a description of how the program works.
Current Solution
begin
procedure usage;
begin
outstring(1, "Usage: please provide a mode and a string to encode/decode\n");
stop
end usage;
integer procedure inAsciiChar;
begin
integer ch;
comment For some reason '%' needs to be represented as '\x25'.
Also, extra single quote needed to close backtick in string;
inchar(
0,
"\x01\x02\x03\x04\x05\x06\x07\x08\t\n\x0b\x0c\r\x0e\x0f"
"\x10\x11\x12\x13\x14\x15\x16\x17\x18\x19\x1a\x1b\x1c\x1d\x1e\x1f"
" !\"#$\x25&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNO"
"PQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|}~\x7f'",
ch
);
if ch >= 129 then ch := 0;
inAsciiChar := ch
end inAsciiChar;
integer procedure inCharArray(s, maxLen);
value maxLen;
integer array s;
integer maxLen;
begin
integer len, ch;
len := 0;
inloop:
ch := inAsciiChar;
if ch != 0 & len < maxLen then
begin
len := len + 1;
s[len] := ch;
goto inloop
end;
inCharArray := len
end inCharArray;
procedure outAsciiChar(ch);
value ch;
integer ch;
begin
comment For some reason '%' needs to be represented as '\x25'.
Also, extra single quote needed to close backtick in string;
outchar(
1,
"\x01\x02\x03\x04\x05\x06\x07\x08\t\n\x0b\x0c\r\x0e\x0f"
"\x10\x11\x12\x13\x14\x15\x16\x17\x18\x19\x1a\x1b\x1c\x1d\x1e\x1f"
" !\"#$\x25&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNO"
"PQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|}~\x7f'",
ch
)
end outAsciiChar;
procedure outCharArray(s, len);
value len;
integer array s;
integer len;
begin
integer i;
for i := 1 step 1 until len do outAsciiChar(s[i])
end outCharArray;
comment Input mode. Return the following:
- -1 if invalid mode
- 0 if decode
- 1 if encode;
integer procedure inMode(s, len);
value len;
integer array s;
integer len;
begin
integer mode;
comment Assume invalid mode;
mode := -1;
comment Length must be 6 and the last 4 characters must be
c (99) o (111) d (100) e(101);
if len = 6 & s[3] = 99 & s[4] = 111 & s[5] = 100 & s[6] = 101 then
begin
comment Indicate encode if first 2 characters are e (101) and n (110).
Indicate decode if first 2 characters are d (100) and e (101);
if s[1] = 101 & s[2] = 110 then mode := 1
else if s[1] = 100 & s[2] = 101 then mode := 0
end;
inMode := mode
end inMode;
comment Returns output length;
integer procedure base64Encode(inStr, inLen, outStr);
value inLen;
integer array inStr, outStr;
integer inLen;
begin
integer outLen, i, n1, n2, n3, u;
outLen := 0;
for i := 1 step 3 until inLen do
begin
comment Convert current 3 characters into 24-bit word, using zero
if past end of string;
n1 := inStr[i];
n2 := if i + 1 <= inLen then inStr[i + 1] else 0;
n3 := if i + 2 <= inLen then inStr[i + 2] else 0;
u := 65536 * n1 + 256 * n2 + n3; comment (n1 << 16) | (n2 << 8) | n3;
comment Convert 24-bit word to 4 character code and append to output
string, using pad if past end of string;
outStr[outLen + 1] := codeToBase64Char(inLen, i, u % 262144); comment u >> 18;
outStr[outLen + 2] := codeToBase64Char(inLen, i, u % 4096); comment u >> 12;
outStr[outLen + 3] := codeToBase64Char(inLen, i + 1, u % 64); comment u >> 6;
outStr[outLen + 4] := codeToBase64Char(inLen, i + 2, u);
outLen := outLen + 4
end;
base64Encode := outLen
end base64Encode;
integer procedure mod(x, n);
value x, n;
integer x, n;
begin
mod := x - n * (x % n)
end mod;
integer procedure codeToBase64Char(inLen, inIdx, u);
value inLen, inIdx, u;
integer inLen, inIdx, u;
begin
integer idx, ch;
comment Get 6-bit index from code;
idx := mod(u, 64);
comment
If past end of string, use pad character, = (61)
Else use the following:
- 0 ... 25 -> A (65) ... Z (90)
- 26 ... 51 -> a (97) ... z (122)
- 52 ... 61 -> 0 (48) ... 9 (57)
- 62 -> + (43)
- 63 -> / (47);
if inIdx > inLen then ch := 61
else if idx >= 0 & idx <= 25 then ch := 65 + idx
else if idx >= 26 & idx <= 51 then ch := 97 - 26 + idx
else if idx >= 52 & idx <= 61 then ch := 48 - 52 + idx
else if idx = 62 then ch := 43
else ch := 47;
codeToBase64Char := ch
end codeToBase64Char;
comment Returns output length if valid Base64 string, negative otherwise;
integer procedure base64Decode(inStr, inLen, outStr);
value inLen;
integer array inStr, outStr;
integer inLen;
begin
integer outLen, padLen, i, n1, n2, n3, n4, u;
comment Assume invalid Base64 string;
outLen := -1;
comment Validate input length and number of trailing pad characters;
padLen := countTrailingPads(inStr, inLen);
if mod(inLen, 4) = 0 & padLen <= 2 then
begin
outLen := 0;
i := 1;
inLen := inLen - padLen;
decloop:
if i <= inLen - 1 & outLen >= 0 then
begin
comment Convert current 3 characters into 24-bit word, using zero
if past end of string. If any invalid characters, indicate
invalid input;
n1 := base64CharToIndex(inStr[i]);
n2 := base64CharToIndex(inStr[i + 1]);
n3 := if i + 2 <= inLen then base64CharToIndex(inStr[i + 2]) else 0;
n4 := if i + 3 <= inLen then base64CharToIndex(inStr[i + 3]) else 0;
if n1 < 0 | n2 < 0 | n3 < 0 | n4 < 0 then outLen := -1
else
begin
comment (n1 << 18) | (n2 << 12) | (n3 << 6) | n4;
u := 262144 * n1 + 4096 * n2 + 64 * n3 + n4;
comment Convert 24-bit code to characters and append to output
string;
codeToOutStr(outStr, outLen, inLen, i, u % 65536); comment u >> 16;
codeToOutStr(outStr, outLen, inLen, i + 2, u % 256); comment u >> 8;
codeToOutStr(outStr, outLen, inLen, i + 3, u)
end;
i := i + 4;
goto decloop
end
end;
base64Decode := outLen
end base64Decode;
comment Returns Base64 index if valid Base64 character, negative otherwise;
integer procedure base64CharToIndex(ch);
value ch;
integer ch;
begin
integer idx;
comment
- A (65) ... Z (90) -> 0 ... 25
- a (97) ... z (122) -> 26 ... 51
- 0 (48) ... 9 (57) -> 52 ... 61
- + (43) -> 62
- / (47) -> 63
- else -> -1;
if ch >= 65 & ch <= 90 then idx := ch - 65
else if ch >= 97 & ch <= 122 then idx := ch - 97 + 26
else if ch >= 48 & ch <= 57 then idx := ch - 48 + 52
else if ch = 43 then idx := 62
else if ch = 47 then idx := 63
else idx := -1;
base64CharToIndex := idx
end base64CharToIndex;
integer procedure countTrailingPads(s, len);
value len;
integer array s;
integer len;
begin
integer padLen, i;
comment Pad character is = (61);
padLen := 0;
i := len;
padloop:
if i >= 1 & s[i] = 61 then
begin
padLen := padLen + 1;
i := i - 1;
goto padloop
end;
countTrailingPads := padLen
end countTrailingPads;
procedure codeToOutStr(outStr, outLen, inLen, idx, u);
value u;
integer array outStr;
integer outLen, inLen, idx, u;
begin
if idx <= inLen then
begin
outLen := outLen + 1;
outStr[outLen] := mod(u, 256)
end
end codeToOutStr;
integer argc, inLen, outLen, mode;
comment inStr is the input array, outStr is the output array.
outStr must be big enough to hold the longest decode string
(ceil[256 * 4 / 3] = 342);
integer array inStr[1:256], outStr[1:342];
comment Get number of parameters. Exit if too few;
ininteger(0, argc);
if argc < 2 then usage;
comment Get mode as a string as integer array. Exit if invalid;
inLen := inCharArray(inStr, 256);
mode := inMode(inStr, inLen);
if mode < 0 then usage;
comment Get string to encode or decode as integer array. Exit if empty;
inLen := inCharArray(inStr, 256);
if inLen < 1 then usage;
comment If encode mode, Base64 encode string;
if mode = 1 then outLen := base64Encode(inStr, inLen, outStr)
else
begin
comment Base64 decode string. Exit if invalid Base64 string;
outLen := base64Decode(inStr, inLen, outStr);
if outLen < 0 then usage
end;
comment Output Base64 encode/decode string;
outCharArray(outStr, outLen);
outstring(1, "\n")
end
Base64 Encode Decode in ALGOL 60 was written by:
- rzuckerm
If you see anything you'd like to change or update, please consider contributing.
How to Implement the Solution
No 'How to Implement the Solution' section available. Please consider contributing.
How to Run the Solution
No 'How to Run the Solution' section available. Please consider contributing.