Adder-rounder circuitry for specialized processing block in programmable logic device
First Claim
1. Combined adding and rounding circuitry for a programmable logic device, for adding two multi-bit input numbers and rounding a resulting sum to a user-programmable bit position selectable from among a subset of available bit positions, said combined rounding and adding circuitry comprising:
- multi-bit addition circuitry; and
input circuitry for (a) accepting, in each bit position, bits of said two multi-bit input numbers and (b) accepting, for each respective bit position in said subset, an additional input of a rounding bit indicative of whether said respective bit position is said user-programmable bit position, said input circuitry outputting data to said multi-bit addition circuitry in a format common to each bit position regardless of the number of inputs to said input circuitry at said bit position.
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Abstract
Adder/rounder circuitry for use in a programmable logic device computes a rounded sum quickly, and ideally within one clock cycle. The rounding position is selectable within a range of bit positions. In an input stage, for each bit position in that range, bits from both addends and a rounding bit are processed, while for each bit position outside that range only bits from both addends are processed. The input stage processing aligns its output in a common format for bits within and outside the range. The input processing may include 3:2 compression for bit positions within the range and 2:2 compression for bit positions outside the range, so that further processing is performed for all bit positions on a sum vector and a carry vector. Computation of the sum proceeds substantially simultaneously with and without the rounding input, and rounding logic makes a selection later in the computation.
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Citations
29 Claims
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1. Combined adding and rounding circuitry for a programmable logic device, for adding two multi-bit input numbers and rounding a resulting sum to a user-programmable bit position selectable from among a subset of available bit positions, said combined rounding and adding circuitry comprising:
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multi-bit addition circuitry; and input circuitry for (a) accepting, in each bit position, bits of said two multi-bit input numbers and (b) accepting, for each respective bit position in said subset, an additional input of a rounding bit indicative of whether said respective bit position is said user-programmable bit position, said input circuitry outputting data to said multi-bit addition circuitry in a format common to each bit position regardless of the number of inputs to said input circuitry at said bit position. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26)
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27. A method of rounding a sum, computed by circuitry for adding two multi-bit input numbers in a programmable logic device, to a user-programmable bit position selectable from among a subset of available bit positions, said method comprising:
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for each bit position outside said subset, processing a bit from each of said multi-bit numbers using a first circuit that inputs two bits and produces a first output having a first number of output bits; for each respective bit position in said subset, processing a bit from each of said multi-bit numbers with a rounding input indicative of whether said respective bit position is said user-programmable bit position, using a second circuit that inputs three bits and produces a second output having said first number of output bits; and combining said first and second outputs to produce a rounded sum. - View Dependent Claims (28, 29)
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Specification