concrete/docs/dev/api/concrete.fhe.mlir.processors.process_rounding.md

module concrete.fhe.mlir.processors.process_rounding

Declaration of ProcessRounding graph processor.

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class ProcessRounding

ProcessRounding graph processor, to analyze rounding and support regular operations on it.

method __init__

__init__(rounding_exactness: Exactness)

---

method apply

apply(graph: Graph)

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method process_predecessors

process_predecessors(graph: Graph, node: Node)

Process predecessors of the rounding.

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method process_successors

process_successors(graph: Graph, node: Node)

Process successors of the rounding.

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method replace_with_tlu

replace_with_tlu(graph: Graph, node: Node)

Replace rounding node with a TLU node that simulates rounding.

This is a special case where:

• user wanted to remove 1-bits
• there was an overflow
• overflow protection was on

Let's say user wanted to remove 1-bit from 3-bits, but there was an overflow:

• [0, 1, 2, 3, 4, 5, 6, 7] would be mapped to [0, 2, 2, 4, 4, 6, 6, 8]
• or in the actual implementation [(0)00, (0)01, (0)01, (0)10, (0)10, (0)11, (0)11, (1)00]
• (first bit is the padding bit, which is overwritten on overflows)
• so the input is 3-bits and the output needs to be 3-bits to store the result
• which can't be achieved with rounding
• so we just replace the rounding with a TLU
• using the table [0, 2, 2, 4, 4, 6, 6, 8]