.. _STRENGTH_REDUCTION_ADDERS_ALLOWED_PER_MULTIPLIER:

STRENGTH_REDUCTION_ADDERS_ALLOWED_PER_MULTIPLIER
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Strength reduction is an optimization that
converts multiply-by-constant into shifts and additions::

    Info: StrengthReduction: Replacing multiply by constant (i26 33038) with 3 adders:
            - (1 << 1) + (1 << 4) + (1 << 8) + (1 << 15)

The STRENGTH_REDUCTION_ADDERS_ALLOWED_PER_MULTIPLIER constraint allows you to
tune the number of adders allowed per multiplier (default is 3).
Strength reduction for multiply-by-constants will not be performed if this requires
more adders than allowed::

    i26 16828 is composed of 4 adders:
    - (1 << 2) + (1 << 6) + (1 << 7) + (1 << 8) + (1 << 14)
    Skipping conversion otherwise would need too many additions.

In this example, we would need 4 adders which is more than the default of 3,
meaning strength reduction will not occur and LegUp will keep the multiplier.

**Category**

HLS Constraints

**Value Type**

Integer

**Valid Values**

Positive Integer

**Default Value**

3

**Location Where Default is Specified**

``examples/legup.tcl``

**Dependencies**

:ref:`STRENGTH_REDUCTION` must be on

**Applicable Flows**

All devices and flows

**Test Status**

Actively in-use

**Examples**

    ``set_parameter STRENGTH_REDUCTION_ADDERS_ALLOWED_PER_MULTIPLIER 3``

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