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To do this, the algorithm treats each integer as an ordered collection of ALU-size fragments, arranged from most-significant (MS) to least-significant (LS) or vice versa. For example, in the case of an 8-bit ALU, the 24-bit integer 0x123456 would be treated as a collection of three 8-bit fragments: 0x12 (MS), 0x34, and 0x56 (LS). Since the size ...
(With 16-bit unsigned saturation, adding any positive amount to 65535 would yield 65535.) Some processors can generate an exception if an arithmetic result exceeds the available precision. Where necessary, the exception can be caught and recovered from—for instance, the operation could be restarted in software using arbitrary-precision ...
For 8-bit integers the table of quarter squares will have 2 9 −1=511 entries (one entry for the full range 0..510 of possible sums, the differences using only the first 256 entries in range 0..255) or 2 9 −1=511 entries (using for negative differences the technique of 2-complements and 9-bit masking, which avoids testing the sign of ...
An 8-bit register can store 2 8 different values. The range of integer values that can be stored in 8 bits depends on the integer representation used. With the two most common representations, the range is 0 through 255 (2 8 − 1) for representation as an binary number, and −128 (−1 × 2 7) through 127 (2 7 − 1) for representation as two's complement.
When the data word is divided into 8-bit blocks, as in the example above, two 8-bit sums result and are combined into a 16-bit Fletcher checksum. Usually, the second sum will be multiplied by 256 and added to the simple checksum, effectively stacking the sums side-by-side in a 16-bit word with the simple checksum at the least significant end.
For example, two 4-bit ALU chips could be arranged side by side, with control lines between them, to form an 8-bit ALU (result need not be power of two, e.g. three 1-bit units can make a 3-bit ALU, [2] thus 3-bit (or n-bit) CPU, while 3-bit, or any CPU with higher odd number of bits, hasn't been manufactured and sold in volume). Four 4-bit ALU ...
The very fastest shifters are implemented as full crossbars, in a manner similar to the 4-bit shifter depicted above, only larger. These incur the least delay, with the output always a single gate delay behind the input to be shifted (after allowing the small time needed for the shift count decoder to settle; this penalty, however, is only incurred when the shift count changes).
The result should be 510 which is the 9-bit value 111111110 in binary. The 8 least significant bits always stored in the register would be 11111110 binary (254 decimal) but since there is carry out of bit 7 (the eight bit), the carry is set, indicating that the result needs 9 bits. The valid 9-bit result is the concatenation of the carry flag ...