9.4. Arithmetic Operation Considerations
- Introduce floating-point arithmetic operations only when necessary.
- The Intel® FPGA SDK for OpenCL™ Offline Compiler 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.
- 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:
- 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.
- 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.
- If you work with a small set of input values, consider using a LUT instead.
- 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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