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< title > Base64< / title >
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< h1 > < a href = "../index.html" >
< img src = "../docs-src/Figures/Inform.png" height = 72" >
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< ul > < li > < a href = "../compiler.html" > compiler tools< / a > < / li >
< li > < a href = "../other.html" > other tools< / a > < / li >
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< li > < a href = "../extensions.html" > extensions and kits< / a > < / li >
< li > < a href = "../units.html" > unit test tools< / a > < / li >
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< / ul > < h2 > Other Tools< / h2 > < ul >
< li > < a href = "index.html" > < span class = "selectedlink" > inblorb< / span > < / a > < / li >
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< li > < a href = "../indoc/index.html" > indoc< / a > < / li >
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< li > < a href = "../inrtps/index.html" > inrtps< / a > < / li >
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< / ul > < h2 > Foundation< / h2 > < ul >
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< li > < a href = "../../../inweb/docs/foundation-module/index.html" > foundation< / a > < / li >
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<!-- Weave of 'Base64' generated by 7 -->
< ul class = "crumbs" > < li > < a href = "../index.html" > Home< / a > < / li > < li > < a href = "../other.html" > Other Tools< / a > < / li > < li > < a href = "index.html" > inblorb< / a > < / li > < li > < a href = "index.html#3" > Chapter 3: Other Material< / a > < / li > < li > < b > Base64< / b > < / li > < / ul > < p class = "purpose" > To produce base64-encoded story files ready for in-browser play by a Javascript-based interpreter such as Parchment.< / p >
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< p class = "inwebparagraph" > < a id = "SP1" > < / a > < b > § 1. < / b > The Base64 encoding scheme is defined by the Internet standard RFC 1113.
Broadly, the idea is to take a binary stream of bytes, break it into
threes, and then convert this into a sequence of four emailable
characters. To encode 24 bits in four characters, we need six bits per
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character, so we need \(2^6 = 64\) characters in all. Since \(64 = 26 +
26 + 10 + 2\(, we can nearly get there with alphanumeric characters alone,
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adding just two others — conventionally, plus and forward-slash.
That's more or less the whole thing, except that we use an equals sign
to indicate incompleteness of the final triplet (which might have only
1 or 2 bytes in it).
< / p >
< p class = "inwebparagraph" > RFC 1113 permits white space to be used freely, including in particular
line breaks, but we don't avail ourselves.
< / p >
< pre class = "display" >
< span class = "reserved" > char< / span > < span class = "plain" > *< / span > < span class = "identifier" > RFC1113_table< / span > < span class = "plain" > = < / span > < span class = "string" > "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/="< / span > < span class = "plain" > ;< / span >
< / pre >
< p class = "inwebparagraph" > < / p >
< p class = "inwebparagraph" > < a id = "SP2" > < / a > < b > § 2. < / b > The encoding routine is as follows.
< / p >
< pre class = "display" >
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< span class = "reserved" > void< / span > < span class = "plain" > < / span > < span class = "functiontext" > Base64::encode< button class = "popup" onclick = "togglePopup('usagePopup118')" > ...< span class = "popuptext" id = "usagePopup118" > Usage of < b > Base64::encode< / b > :< br > Releaser - < a href = "3-rls.html#SP6_5" > § 6.5< / a > < / span > < / button > < / span > < span class = "plain" > (< / span > < span class = "reserved" > filename< / span > < span class = "plain" > *< / span > < span class = "identifier" > in_filename< / span > < span class = "plain" > , < / span > < span class = "reserved" > filename< / span > < span class = "plain" > *< / span > < span class = "identifier" > out_filename< / span > < span class = "plain" > , < / span > < span class = "reserved" > text_stream< / span > < span class = "plain" > *< / span > < span class = "identifier" > top< / span > < span class = "plain" > , < / span > < span class = "reserved" > text_stream< / span > < span class = "plain" > *< / span > < span class = "identifier" > tail< / span > < span class = "plain" > ) {< / span >
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< span class = "reserved" > FILE< / span > < span class = "plain" > *< / span > < span class = "identifier" > IN< / span > < span class = "plain" > = < / span > < span class = "functiontext" > < a href = "../../../inweb/docs/foundation-module/6-bf.html#SP8" > BinaryFiles::open_for_reading< / a > < / span > < span class = "plain" > (< / span > < span class = "identifier" > in_filename< / span > < span class = "plain" > );< / span >
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< span class = "reserved" > text_stream< / span > < span class = "plain" > < / span > < span class = "identifier" > TO_struct< / span > < span class = "plain" > ;< / span >
< span class = "reserved" > text_stream< / span > < span class = "plain" > *< / span > < span class = "identifier" > TO< / span > < span class = "plain" > = & < / span > < span class = "identifier" > TO_struct< / span > < span class = "plain" > ;< / span >
< span class = "reserved" > if< / span > < span class = "plain" > (< / span > < span class = "identifier" > STREAM_OPEN_TO_FILE< / span > < span class = "plain" > (< / span > < span class = "identifier" > TO< / span > < span class = "plain" > , < / span > < span class = "identifier" > out_filename< / span > < span class = "plain" > , < / span > < span class = "constant" > UTF8_ENC< / span > < span class = "plain" > ) == < / span > < span class = "constant" > FALSE< / span > < span class = "plain" > )< / span >
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< span class = "functiontext" > < a href = "1-be.html#SP2" > BlorbErrors::fatal_fs< / a > < / span > < span class = "plain" > (< / span > < span class = "string" > "can't open base-64 encoded story file for output"< / span > < span class = "plain" > , < / span > < span class = "identifier" > out_filename< / span > < span class = "plain" > );< / span >
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< span class = "functiontext" > < a href = "3-bs6.html#SP2" > Base64::encode_inner< / a > < / span > < span class = "plain" > (< / span > < span class = "identifier" > TO< / span > < span class = "plain" > , < / span > < span class = "identifier" > IN< / span > < span class = "plain" > , < / span > < span class = "identifier" > top< / span > < span class = "plain" > , < / span > < span class = "identifier" > tail< / span > < span class = "plain" > );< / span >
< span class = "functiontext" > < a href = "../../../inweb/docs/foundation-module/6-bf.html#SP8" > BinaryFiles::close< / a > < / span > < span class = "plain" > (< / span > < span class = "identifier" > IN< / span > < span class = "plain" > );< / span >
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< span class = "identifier" > STREAM_CLOSE< / span > < span class = "plain" > (< / span > < span class = "identifier" > TO< / span > < span class = "plain" > );< / span >
< span class = "plain" > }< / span >
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< span class = "reserved" > void< / span > < span class = "plain" > < / span > < span class = "functiontext" > Base64::encode_inner< button class = "popup" onclick = "togglePopup('usagePopup119')" > ...< span class = "popuptext" id = "usagePopup119" > Usage of < b > Base64::encode_inner< / b > :< br > none< / span > < / button > < / span > < span class = "plain" > (< / span > < span class = "constant" > OUTPUT_STREAM< / span > < span class = "plain" > , < / span > < span class = "reserved" > FILE< / span > < span class = "plain" > *< / span > < span class = "identifier" > IN< / span > < span class = "plain" > , < / span > < span class = "reserved" > text_stream< / span > < span class = "plain" > *< / span > < span class = "identifier" > top< / span > < span class = "plain" > , < / span > < span class = "reserved" > text_stream< / span > < span class = "plain" > *< / span > < span class = "identifier" > tail< / span > < span class = "plain" > ) {< / span >
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< span class = "reserved" > if< / span > < span class = "plain" > (< / span > < span class = "identifier" > top< / span > < span class = "plain" > ) < / span > < span class = "identifier" > WRITE< / span > < span class = "plain" > (< / span > < span class = "string" > "%S"< / span > < span class = "plain" > , < / span > < span class = "identifier" > top< / span > < span class = "plain" > );< / span >
< span class = "reserved" > while< / span > < span class = "plain" > (< / span > < span class = "constant" > TRUE< / span > < span class = "plain" > ) {< / span >
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< span class = "reserved" > int< / span > < span class = "plain" > < / span > < span class = "identifier" > triplet< / span > < span class = "plain" > [3], < / span > < span class = "identifier" > triplet_size< / span > < span class = "plain" > = < / span > < span class = "constant" > 0< / span > < span class = "plain" > ;< / span >
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< < span class = "cwebmacro" > Read the triplet of binary bytes, storing 0 to 3 in the size read< / span > < span class = "cwebmacronumber" > 2.1< / span > > < span class = "plain" > ;< / span >
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< span class = "reserved" > if< / span > < span class = "plain" > (< / span > < span class = "identifier" > triplet_size< / span > < span class = "plain" > == < / span > < span class = "constant" > 0< / span > < span class = "plain" > ) < / span > < span class = "reserved" > break< / span > < span class = "plain" > ;< / span >
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< span class = "reserved" > int< / span > < span class = "plain" > < / span > < span class = "identifier" > quartet< / span > < span class = "plain" > [4];< / span >
< < span class = "cwebmacro" > Convert triplet to a quartet< / span > < span class = "cwebmacronumber" > 2.2< / span > > < span class = "plain" > ;< / span >
< span class = "reserved" > int< / span > < span class = "plain" > < / span > < span class = "identifier" > i< / span > < span class = "plain" > ; < / span > < span class = "reserved" > for< / span > < span class = "plain" > (< / span > < span class = "identifier" > i< / span > < span class = "plain" > =0; < / span > < span class = "identifier" > i< / span > < span class = "plain" > < 4; < / span > < span class = "identifier" > i< / span > < span class = "plain" > ++) < / span > < span class = "identifier" > PUT< / span > < span class = "plain" > (< / span > < span class = "identifier" > RFC1113_table< / span > < span class = "plain" > [< / span > < span class = "identifier" > quartet< / span > < span class = "plain" > [< / span > < span class = "identifier" > i< / span > < span class = "plain" > ]]);< / span >
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< span class = "reserved" > if< / span > < span class = "plain" > (< / span > < span class = "identifier" > triplet_size< / span > < span class = "plain" > < < / span > < span class = "constant" > 3< / span > < span class = "plain" > ) < / span > < span class = "reserved" > break< / span > < span class = "plain" > ;< / span >
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< span class = "plain" > }< / span >
< span class = "reserved" > if< / span > < span class = "plain" > (< / span > < span class = "identifier" > tail< / span > < span class = "plain" > ) < / span > < span class = "identifier" > WRITE< / span > < span class = "plain" > (< / span > < span class = "string" > "%S"< / span > < span class = "plain" > , < / span > < span class = "identifier" > tail< / span > < span class = "plain" > );< / span >
< span class = "plain" > }< / span >
< / pre >
< p class = "inwebparagraph" > < / p >
< p class = "inwebparagraph" > < a id = "SP2_1" > < / a > < b > § 2.1. < / b > If the file ends in mid-triplet, we pad out with zeros.
< / p >
< p class = "macrodefinition" > < code class = "display" >
< < span class = "cwebmacrodefn" > Read the triplet of binary bytes, storing 0 to 3 in the size read< / span > < span class = "cwebmacronumber" > 2.1< / span > > =
< / code > < / p >
< pre class = "displaydefn" >
< span class = "identifier" > triplet< / span > < span class = "plain" > [0] = < / span > < span class = "identifier" > fgetc< / span > < span class = "plain" > (< / span > < span class = "identifier" > IN< / span > < span class = "plain" > );< / span >
< span class = "reserved" > if< / span > < span class = "plain" > (< / span > < span class = "identifier" > triplet< / span > < span class = "plain" > [0] != < / span > < span class = "identifier" > EOF< / span > < span class = "plain" > ) {< / span >
< span class = "identifier" > triplet_size< / span > < span class = "plain" > ++;< / span >
< span class = "identifier" > triplet< / span > < span class = "plain" > [1] = < / span > < span class = "identifier" > fgetc< / span > < span class = "plain" > (< / span > < span class = "identifier" > IN< / span > < span class = "plain" > );< / span >
< span class = "reserved" > if< / span > < span class = "plain" > (< / span > < span class = "identifier" > triplet< / span > < span class = "plain" > [1] != < / span > < span class = "identifier" > EOF< / span > < span class = "plain" > ) {< / span >
< span class = "identifier" > triplet_size< / span > < span class = "plain" > ++;< / span >
< span class = "identifier" > triplet< / span > < span class = "plain" > [2] = < / span > < span class = "identifier" > fgetc< / span > < span class = "plain" > (< / span > < span class = "identifier" > IN< / span > < span class = "plain" > );< / span >
< span class = "reserved" > if< / span > < span class = "plain" > (< / span > < span class = "identifier" > triplet< / span > < span class = "plain" > [2] != < / span > < span class = "identifier" > EOF< / span > < span class = "plain" > )< / span >
< span class = "identifier" > triplet_size< / span > < span class = "plain" > ++;< / span >
< span class = "plain" > }< / span >
< span class = "plain" > }< / span >
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< span class = "reserved" > int< / span > < span class = "plain" > < / span > < span class = "identifier" > i< / span > < span class = "plain" > ; < / span > < span class = "reserved" > for< / span > < span class = "plain" > (< / span > < span class = "identifier" > i< / span > < span class = "plain" > =< / span > < span class = "identifier" > triplet_size< / span > < span class = "plain" > ; < / span > < span class = "identifier" > i< / span > < span class = "plain" > < 3; < / span > < span class = "identifier" > i< / span > < span class = "plain" > ++) < / span > < span class = "identifier" > triplet< / span > < span class = "plain" > [< / span > < span class = "identifier" > i< / span > < span class = "plain" > ] = < / span > < span class = "constant" > 0< / span > < span class = "plain" > ;< / span >
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< / pre >
< p class = "inwebparagraph" > < / p >
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< p class = "endnote" > This code is used in < a href = "3-bs6.html#SP2" > § 2< / a > .< / p >
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< p class = "inwebparagraph" > < a id = "SP2_2" > < / a > < b > § 2.2. < / b > < code class = "display" >
< < span class = "cwebmacrodefn" > Convert triplet to a quartet< / span > < span class = "cwebmacronumber" > 2.2< / span > > =
< / code > < / p >
< pre class = "displaydefn" >
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< span class = "reserved" > int< / span > < span class = "plain" > < / span > < span class = "identifier" > i< / span > < span class = "plain" > ; < / span > < span class = "reserved" > for< / span > < span class = "plain" > (< / span > < span class = "identifier" > i< / span > < span class = "plain" > =0; < / span > < span class = "identifier" > i< / span > < span class = "plain" > < 4; < / span > < span class = "identifier" > i< / span > < span class = "plain" > ++) < / span > < span class = "identifier" > quartet< / span > < span class = "plain" > [< / span > < span class = "identifier" > i< / span > < span class = "plain" > ] = < / span > < span class = "constant" > 0< / span > < span class = "plain" > ;< / span >
< span class = "identifier" > quartet< / span > < span class = "plain" > [0] += (< / span > < span class = "identifier" > triplet< / span > < span class = "plain" > [0] & < / span > < span class = "constant" > 0xFC< / span > < span class = "plain" > ) > > < / span > < span class = "constant" > 2< / span > < span class = "plain" > ;< / span >
< span class = "identifier" > quartet< / span > < span class = "plain" > [1] += (< / span > < span class = "identifier" > triplet< / span > < span class = "plain" > [0] & < / span > < span class = "constant" > 0x03< / span > < span class = "plain" > ) < < < / span > < span class = "constant" > 4< / span > < span class = "plain" > ;< / span >
< span class = "identifier" > quartet< / span > < span class = "plain" > [1] += (< / span > < span class = "identifier" > triplet< / span > < span class = "plain" > [1] & < / span > < span class = "constant" > 0xF0< / span > < span class = "plain" > ) > > < / span > < span class = "constant" > 4< / span > < span class = "plain" > ;< / span >
< span class = "identifier" > quartet< / span > < span class = "plain" > [2] += (< / span > < span class = "identifier" > triplet< / span > < span class = "plain" > [1] & < / span > < span class = "constant" > 0x0F< / span > < span class = "plain" > ) < < < / span > < span class = "constant" > 2< / span > < span class = "plain" > ;< / span >
< span class = "identifier" > quartet< / span > < span class = "plain" > [2] += (< / span > < span class = "identifier" > triplet< / span > < span class = "plain" > [2] & < / span > < span class = "constant" > 0xC0< / span > < span class = "plain" > ) > > < / span > < span class = "constant" > 6< / span > < span class = "plain" > ;< / span >
< span class = "identifier" > quartet< / span > < span class = "plain" > [3] += (< / span > < span class = "identifier" > triplet< / span > < span class = "plain" > [2] & < / span > < span class = "constant" > 0x3F< / span > < span class = "plain" > ) < < < / span > < span class = "constant" > 0< / span > < span class = "plain" > ;< / span >
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< span class = "reserved" > switch< / span > < span class = "plain" > (< / span > < span class = "identifier" > triplet_size< / span > < span class = "plain" > ) {< / span >
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< span class = "reserved" > case< / span > < span class = "plain" > < / span > < span class = "constant" > 1< / span > < span class = "plain" > : < / span > < span class = "identifier" > quartet< / span > < span class = "plain" > [2] = < / span > < span class = "constant" > 64< / span > < span class = "plain" > ; < / span > < span class = "identifier" > quartet< / span > < span class = "plain" > [3] = < / span > < span class = "constant" > 64< / span > < span class = "plain" > ; < / span > < span class = "reserved" > break< / span > < span class = "plain" > ;< / span >
< span class = "reserved" > case< / span > < span class = "plain" > < / span > < span class = "constant" > 2< / span > < span class = "plain" > : < / span > < span class = "identifier" > quartet< / span > < span class = "plain" > [3] = < / span > < span class = "constant" > 64< / span > < span class = "plain" > ; < / span > < span class = "reserved" > break< / span > < span class = "plain" > ;< / span >
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< span class = "plain" > }< / span >
< / pre >
< p class = "inwebparagraph" > < / p >
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< p class = "endnote" > This code is used in < a href = "3-bs6.html#SP2" > § 2< / a > .< / p >
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< hr class = "tocbar" >
< ul class = "toc" > < li > < a href = "3-wm.html" > Back to 'Website Maker'< / a > < / li > < li > < i > (This section ends Chapter 3: Other Material.)< / i > < / li > < / ul > < hr class = "tocbar" >
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<!-- End of weave -->
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< script >
MathJax = {
tex: {
inlineMath: '$', '$'], ['\\(', '\\)'
},
svg: {
fontCache: 'global'
}
};
< / script >
< script type = "text/javascript" id = "MathJax-script" async
src="https://cdn.jsdelivr.net/npm/mathjax@3/es5/tex-svg.js">
< / script >
< script >
function togglePopup(material_id) {
var popup = document.getElementById(material_id);
popup.classList.toggle("show");
}
< / script >
< link href = "Popups.css" rel = "stylesheet" rev = "stylesheet" type = "text/css" >
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< / main >
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< / body >
< / html >