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Though the multiply instruction became common with the 16-bit generation, [4] at least two 8-bit processors have a multiply instruction: the Motorola 6809, introduced in 1978, [5] and Intel MCS-51 family, developed in 1980, and later the modern Atmel AVR 8-bit microprocessors present in the ATMega, ATTiny and ATXMega microcontrollers.
Brickell [3] has published a similar algorithm that requires greater complexity in the electronics for each digit of the accumulator.. Montgomery multiplication is an alternative algorithm which processes the multiplier "backwards" (least significant digit first) and uses the least significant digit of the accumulator to control whether or not the modulus should be added.
Booth's algorithm examines adjacent pairs of bits of the 'N'-bit multiplier Y in signed two's complement representation, including an implicit bit below the least significant bit, y −1 = 0. For each bit y i, for i running from 0 to N − 1, the bits y i and y i−1 are considered. Where these two bits are equal, the product accumulator P is ...
A Wallace multiplier is a hardware implementation of a binary multiplier, a digital circuit that multiplies two integers. It uses a selection of full and half adders (the Wallace tree or Wallace reduction ) to sum partial products in stages until two numbers are left.
The advantage over 8-bit or 16-bit integers is that the increased dynamic range allows for more detail to be preserved in highlights and shadows for images, and avoids gamma correction. The advantage over 32-bit single-precision floating point is that it requires half the storage and bandwidth (at the expense of precision and range). [5]
Third, m is in [0, R − 1], and therefore T + mN is between 0 and (RN − 1) + (R − 1)N < 2RN. Hence t is less than 2 N , and because it's an integer, this puts t in the range [0, 2 N − 1] . Therefore, reducing t into the desired range requires at most a single subtraction, so the algorithm's output lies in the correct range.
A common example is the Data General Nova, which was a 16-bit design that performed 16-bit math as a series of four 4-bit operations. 4-bits was the word size of a widely available single-chip ALU and thus allowed for inexpensive implementation. Using the definition being applied to the 68000, the Nova would be a 4-bit computer, or 4/16.
In a computer with a full 32-bit by 32-bit multiplier, for example, one could choose B = 2 31 and store each digit as a separate 32-bit binary word. Then the sums x 1 + x 0 and y 1 + y 0 will not need an extra binary word for storing the carry-over digit (as in carry-save adder ), and the Karatsuba recursion can be applied until the numbers to ...