btoa

tool, messaging, algorithm, file format /B too A/ A binary

to ASCII conversion utility.

btoa is a uuencode or base 64 equivalent which addresses

some of the problems with the uuencode standard but not as

many as the base 64 standard. It avoids problems that some

hosts have with spaces (e.g. conversion of groups of spaces

to tabs) by not including them in its character set, but may

still have problems on non-ASCII systems (e.g. EBCDIC).

btoa is primarily used to transfer binary files between

systems across connections which are not eight-bit clean,

e.g. electronic mail.

btoa takes adjacent sets of four binary octets and encodes

them as five ASCII octets using ASCII characters '!' through

to 'u'. Special characters are also used: 'x' marks the

beginning or end of the archive; 'z' marks four consecutive

zeros and 'y' (version 5.2) four consecutive spaces.

Each group of four octets is processed as a 32-bit integer.

Call this 'I'. Let 'D' = 85^4. Divide I by D. Call this

result 'R'. Make I = I - (R * D) to avoid overflow on the

next step. Repeat, for values of D = 85^3, 85^2, 85 and 1.

At each step, to convert R to the output character add decimal

33 (output octet = R + ASCII value for '!'). Five output

octets are produced.

btoa provides some integrity checking in the form of a line

checksum, and facilities for patching corrupted downloads.

The algorithm used by btoa is more efficient than uuencode

or base 64. ASCII files are encoded to about 120% the size of

their binary sources. This compares with 135% for uuencode or

base 64.

C source .

(version 5.2 - ~1994).

Pre-compiled MS-DOS versions are also available.

(1997-08-08)