Next we discuss the construction of fixed and¬
adaptive models.
 The subsequent section details the compression¬
efficiency and execution time
 of the programs, including the effect of¬
different arithmetic word lengths on
 compression efficiency.
 Finally, we outline a few applications where¬
arithmetic coding is appropriate.
 .sh "Data compression"
 .pp
 To many, data compression conjures up an¬
assortment of \fIad hoc\fR
 techniques such as converting spaces in text to¬
tabs, creating special codes
 for common words, or run-length coding of picture¬
data (eg see Held, 1984).
 .[
 Held 1984 data compression techniques¬
applications
 .]
 This contrasts with the more modern model-based¬
paradigm for
 coding, where from an \fIinput string\fR of¬
symbols and a \fImodel\fR, an
 \fIencoded string\fR is produced which is¬
(usually) a compressed version of
 the input.
 The decoder, which must have access to the same¬
model,
 regenerates the exact input string from the¬
encoded string.
 Input symbols are drawn from some well-defined¬
set such as the ASCII or