Intel® FPGA SDK for OpenCL™ Standard Edition: Best Practices Guide

ID 683176
Date 9/24/2018
Public
Document Table of Contents

8.4. Arithmetic Operation Considerations

Select the appropriate arithmetic operation for your OpenCL™ application to avoid excessive FPGA area usage.
  1. Introduce floating-point arithmetic operations only when necessary.
  2. The defaults floating-point constants to double data type. Add an f designation to the constant to make it a single precision floating-point operation.

    For example, the arithmetic operation sin(1.0) represents a double precision floating-point sine function. The arithmetic operation sin(1.0f) represents a single precision floating-point sine function.

  3. If you do not require full precision result for a complex function, compute simpler arithmetic operations to approximate the result. Consider the following example scenarios:
    1. Instead of computing the function pow(x,n) where n is a small value, approximate the result by performing repeated squaring operations because they require much less hardware resources and area.
    2. Ensure you are aware of the original and approximated area usages because in some cases, computing a result via approximation might result in excess area usage. For example, the sqrt function is not resource-intensive. Other than a rough approximation, replacing the sqrt function with arithmetic operations that the host has to compute at runtime might result in larger area usage.
    3. If you work with a small set of input values, consider using a LUT instead.

  4. If your kernel performs a complex arithmetic operation with a constant that the offline compiler computes at compilation time (for example, log(PI/2.0)), perform the arithmetic operation on the host instead and pass the result as an argument to the kernel at runtime.

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