Editing Uuencoding (section)

== Formatting mechanism ==
The mechanism of <code>uuencoding</code> repeats the following for every 3 bytes, encoding them into 4 printable characters, each character representing a [[radix-64]] [[numerical digit]]:
# Start with 3 [[bytes]] from the source, 24 [[bit]]s in total.
# Split into 4 6-bit groupings, each representing a value in the range 0 to 63: bits (00-05), (06-11), (12-17) and (18-23).
# Add 32 to each of the values. With the addition of 32 this means that the possible results can be between 32 (" " space) and 95 ("_" [[underline]]). 96 ("`" [[grave accent]]) as the "special character" is a logical extension of this range. Despite space character being documented as the encoding for value of 0, implementations, such as GNU sharutils,<ref>{{Cite web |title=uuencode.c source |url=https://fossies.org/dox/sharutils-4.15.2/uuencode_8c_source.html#l00085 |access-date=2021-06-05 |website=fossies.org |language=en-US}}</ref> actually use the grave accent character to encode zeros in the body of the file as well, never using space.
# Output the ASCII equivalent of these numbers.

If the source length is not divisible by 3, then the last 4-byte section will contain padding bytes to make it cleanly divisible. These bytes are subtracted from the line's <code><length character></code> so that the decoder does not append unwanted characters to the file.

<code>uudecoding</code> is reverse of the above, subtract 32 from each character's ASCII code ([[modulo]] 64 to account for the grave accent usage) to get a 6-bit value, concatenate 4 6-bit groups to get 24 bits, then output 3 bytes.

The encoding process is demonstrated by this table, which shows the derivation of the above encoding for "Cat".

{| class="wikitable"
| style="border-right: 2px solid black" | Original characters
! colspan=8 style="border-right: 2px solid green" | <code>C</code>
! colspan=8 style="border-right: 2px solid green" | <code>a</code>
! colspan=8 style="border-right: 2px solid black" | <code>t</code>
|-
| style="border-right: 2px solid black" | Original ASCII, decimal
! colspan=8 style="border-right: 2px solid green" | 67
! colspan=8 style="border-right: 2px solid green" | 97
! colspan=8 style="border-right: 2px solid black" | 116
|-
| style="border-right: 2px solid black" | ASCII, binary
| 0
| 1
| 0
| 0
| 0
| style="border-right: 2px solid red" |0
| 1
| style="border-right: 2px solid green" | 1
| 0
| 1
| 1
| style="border-right: 2px solid red" | 0
| 0
| 0
| 0
| style="border-right: 2px solid green" | 1
| 0
| style="border-right: 2px solid red" | 1
| 1
| 1
| 0
| 1
| 0
| style="border-right: 2px solid black" | 0
|-
| style="border-right: 2px solid black" | New decimal values
! colspan=6 style="border-right: 2px solid red" | 16
! colspan=6 style="border-right: 2px solid red" | 54
! colspan=6 style="border-right: 2px solid red" | 5
! colspan=6 style="border-right: 2px solid black" | 52
|-
| style="border-right: 2px solid black" | +32
! colspan=6 style="border-right: 2px solid red" | 48
! colspan=6 style="border-right: 2px solid red" | 86
! colspan=6 style="border-right: 2px solid red" | 37
! colspan=6 style="border-right: 2px solid black" | 84
|-
| style="border-right: 2px solid black" | Uuencoded characters
! colspan=6 style="border-right: 2px solid red" | <code>0</code>
! colspan=6 style="border-right: 2px solid red" | <code>V</code>
! colspan=6 style="border-right: 2px solid red" | <code>%</code>
! colspan=6 style="border-right: 2px solid black" | <code>T</code>
|}