| 摘要 |
<p>Device for calculating the parity bits (PS) of a sum (S) of two numbers (A, B).
<??>A parity bit (PA, PB, PS) is associated with each group of m bits (ai, bi, si) which is extracted from the numbers (A, B) and from the sum (S). For each group, a device is produced for calculating the parity bit (PC) associated with the corresponding group extracted from the carry word formed during the addition. This device comprises:
- a first stage (11) for calculating, for all i lying between 1 and m - 1, the values:
pi = ai (+) bi
gi = ai.bi
(+) designating the operation ''EXCLUSIVE OR'',
- a first operator (41a) for calculating, for all i lying between 1 and m - 1, the values Pi and the values Gi satisfying the following recurrence logic equations:
Pi = pi . Pi-1 with P1 = p1
Gi = gi + pi.Gi-1 with G1 = g1
- a second operator (41b) for calculating:
Y = G1 (+) G2 (+) ... (+) Gi (+) ... (+) Gm-1
X = P1 (+) P2 + ... + Pi + ... + Pm-1
- and a third operator (51) for calculating: PC = Y (+) cin . X<*> where cin is the lowest-order carry of the group and where X<*> is the complement of X.
<??>Use in particular in the arithmetic and logic units of computers.
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