Page 125 - Hardware Implementation of Finite-Field Arithmetic

108 Cha pte r F o u r

sel_bd oper next_b
0 −− y
1 00 b/2
2 00 b/4
2 10 (b + a)/4
2 11 (b − a)/4
TABLE 4.1 next _b in function of
sel_bd and oper
For computing next_d the value of corrected_sum must be first
computed; it can be equal to

d, d + p, d + 2p, d − p, d + c, d + c + p, d + c + 2p, d + c − p, d − c,
d − c + p, d − c + 2p,or d − c − p
Tables 4.2 and 4.3 define the value of the control signals for gen-
erating z and corrected_sum.

last b oper sel_correction z
0 10 0 c
0 10 1 p + c
0 11 0 −c
0 11 1 p − c

TABLE 4.2 z in function of oper (last b = 0)

last b oper sel_correction corrected_sum
1 0 − 0 d
1 0 − 1 d + p
1 0 − 2 d + 2p
1 0 − 3 d − p
1 10 0 d + c
1 10 1 d + c + p
1 10 2 d + c + 2p
1 10 3 d + c − p
1 11 0 d − c
1 11 1 d − c + p
1 11 2 d − c + 2p
1 11 3 d − c − p
TABLE 4.3 corrected_sum in function of oper and
sel_correction (last b = 1)