Page 378 - Programming Microcontrollers in C

Coding the Alpha Data 363

h 000001
i 1100
j 000011001
k 1111111
l 1110
m 111100
n 1101
o 0011
p 111111001
q 11111101111
r 0010
s 111101
t 000000
u 111111000
v 111111010
w 0000110111
x 11111101110
y 000011010
z 1111110110

Table 7-1: Huffman Code for Compressing Telephone Book Names

The encoding routine is shown in Listing 7-6. Contained in the
listing of the encoding routine is a look-up table that contains all of the
codes. In this table, the first two entries correspond to a space character
and a new line character. The following entries correspond to the letters
in the alphabet. In other words, the third entry corresponds to the letter
A and the seventh entry corresponds to the letter E. Notice that this
table is defined as external, but it is labeled static so that there is no
linkage to the table outside of the file encode.c.
In operation, this function receives three parameters. The first is
a pointer to an array that contains the data to be encoded. This array
contains a zero terminated string. The second array of unsigned
integers is named array. Its length is the third passed parameter
length. Encoded data are all loaded into this array. All of the local
variables used by encode are straightforward. The variable
bitbase is an unsigned int with its most significant bit set to
one and the remainder of its bits zero. When the function is executed,
the array[] is first filled with zeros. The variable i is initialized