writing the q-least-significant bits of C(s) and an internal variable T(s) into respective first and second shift registers; and

ascertaining for each b(i) whether it constitutes a most-probable symbol (MPS); and

deriving an integer k as a coding parameter indicative of an expectation for the least-probable symbol (LPS); characterized in that

the method comprises the further steps of:

concurrently incrementing the first register contents and decrementing the second register contents by 2.sup.-k and left-shift normalizing both register contents if the second register contains a leading zero, if b(i) is an MPS; and

left-shifting the first register contents by k positions and setting the second register contents to unity, if b(i) is an LPS.

a first (41) and second (59) shift register containing the q-least-significant bits of the compressed stream C(s) and an internal variable T(s); means (31, 33) for characterizing each received symbol as either a most-probable symbol (MPS) or a least-probable symbol (LPS); characterized in that

the apparatus further comprises:

means (9, 35, 39, 47) responsive to an LPS symbol characterization and to a parameter k whose values correspond to a predetermined source alphabet probability interval for shifting out the k-most-significant bits in the first register and zero-filling the k-least-significant bit positions therein, said means further including means for setting the second register contents to unity; and

means (49, 63, 53, 55) for concurrently incrementing the first register contents by 2.sup.-k and decrementing the second register contents by 2.sup.-k, left-shift normalizing (67, 53, 55) both register contents if the second register contains a leading zero in response to an MPS symbol characterization and the parameter k.

a first- (41) and second- (59) shift register containing the q-least-significant bits of the compressed stream and an internal variable; characterized in that

the encoder further comprises:

means (9, 47, 39, 35) responsive to each ordered pair MPS, k for shifting out the k-most-significant bits and zero-filling the k-least-significant bits of the first register and setting (CLEAR) the second register contents to unity; and

a first and second computation loop (49, 51, 53, 37; 63, 65, 55, 57) for additively combining 2.sup.-k to the first register contents and subtractively combining 2.sup.-k from the second register contents, said first and second loop including means (67, 53, 55) for left-shift normalizing both register contents if the second register contains a leading zero responsive to each ordered pair of LPS, k.

writing the q-most significant bits of C(s.b) and an internal variable T(s) into respective first and second shift registers;

deriving an integer k(i) as a coding parameter indicative of an expectation that the decodable symbol is a least-probable symbol (LPS); characterized in that

the method comprises the further steps of:

concurrently decrementing the first and second register contents by 2.sup.-k(i) ;

testing the most-significant bit position of the first register;

left-shift normalizing both register contents if the tested bit position is 1 and decoding the symbol as a most-probable symbol; and

left-shifting the first register contents by k positions and setting the second register contents to unity if the tested bit position is a 0, and decoding the symbol as an LPS.