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#
#
# Nimrod's Runtime Library
# (c) Copyright 2010 Andreas Rumpf
#
# See the file "copying.txt", included in this
# distribution, for details about the copyright.
#
## This module implements a base64 encoder and decoder.
const
cb64 = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"
proc encode*(s: string, lineLen = 75, newLine="\13\10"): string =
## encodes `s` into base64 representation. After `lineLen` characters, a
## `newline` is added.
var total = ((len(s) + 2) div 3) * 4
var numLines = (total + (lineLen - 1)) div lineLen
if numLines > 0: inc(total, (numLines-1) * newLine.len)
result = newString(total)
var i = 0
var r = 0
var currLine = 0
while i < s.len - 2:
var a = ord(s[i])
var b = ord(s[i+1])
var c = ord(s[i+2])
result[r] = cb64[a shr 2]
result[r+1] = cb64[((a and 3) shl 4) or ((b and 0xF0) shr 4)]
result[r+2] = cb64[((b and 0x0F) shl 2) or ((c and 0xC0) shr 6)]
result[r+3] = cb64[c and 0x3F]
inc(r, 4)
inc(i, 3)
inc(currLine, 4)
if currLine >= lineLen and i != s.len-2:
for x in items(newLine):
result[r] = x
inc(r)
currLine = 0
if i < s.len-1:
var a = ord(s[i])
var b = ord(s[i+1])
result[r] = cb64[a shr 2]
result[r+1] = cb64[((a and 3) shl 4) or ((b and 0xF0) shr 4)]
result[r+2] = cb64[((b and 0x0F) shl 2)]
result[r+3] = '='
assert(r+4 == result.len)
elif i < s.len:
var a = ord(s[i])
result[r] = cb64[a shr 2]
result[r+1] = cb64[(a and 3) shl 4]
result[r+2] = '='
result[r+3] = '='
assert(r+4 == result.len)
else:
assert(r == result.len)
proc decodeByte(b: char): int {.inline.} =
case b
of '+': result = ord('>')
of '0'..'9': result = ord(b) + 4
of 'A'..'Z': result = ord(b) - ord('A')
of 'a'..'z': result = ord(b) - 71
else: result = 63
proc decode*(s: string): string =
## decodes a string in base64 representation back into its original form.
## Whitespace is skipped.
const Whitespace = {' ', '\t', '\v', '\r', '\l', '\f'}
var total = ((len(s) + 3) div 4) * 3
# total is an upper bound, as we will skip arbitrary whitespace:
result = newString(total)
var i = 0
var r = 0
while true:
while s[i] in Whitespace: inc(i)
if i < s.len-3:
var a = s[i].decodeByte
var b = s[i+1].decodeByte
var c = s[i+2].decodeByte
var d = s[i+3].decodeByte
result[r] = chr((a shl 2) or ((b shr 4) and 0x03))
result[r+1] = chr((b shl 4) or ((c shr 2) and 0x0F))
result[r+2] = chr((c shl 6) or (d and 0x3F))
inc(r, 3)
inc(i, 4)
else: break
assert i == s.len
# adjust the length:
if i > 0 and s[i-1] == '=':
dec(r)
if i > 1 and s[i-2] == '=': dec(r)
setLen(result, r)
when isMainModule:
assert encode("leasure.") == "bGVhc3VyZS4="
assert encode("easure.") == "ZWFzdXJlLg=="
assert encode("asure.") == "YXN1cmUu"
assert encode("sure.") == "c3VyZS4="
const longText = """Man is distinguished, not only by his reason, but by this
singular passion from other animals, which is a lust of the mind,
that by a perseverance of delight in the continued and indefatigable
generation of knowledge, exceeds the short vehemence of any carnal
pleasure."""
const tests = ["", "abc", "xyz", "man", "leasure.", "sure.", "easure.",
"asure.", longText]
for t in items(tests):
assert decode(encode(t)) == t
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