Common Synthesis Errors - 2021.2 English

Vitis High-Level Synthesis User Guide (UG1399)

Document ID
UG1399
ft:locale
English (United States)
Release Date
2021-12-15
Version
2021.2 English

The following are common use errors when synthesizing math functions. These are often (but not exclusively) caused by converting C functions to C++ to take advantage of synthesis for math functions.

C++ cmath.h

If the C++ cmath.h header file is used, the floating point functions (for example, sinf and cosf) can be used. These result in 32-bit operations in hardware. The cmath.h header file also overloads the standard functions (for example, sin and cos) so they can be used for float and double types.

C math.h

If the C math.h library is used, the single-precision functions (for example, sinf and cosf) are required to synthesize 32-bit floating point operations. All standard function calls (for example, sin and cos) result in doubles and 64-bit double-precision operations being synthesized.

Cautions

When converting C functions to C++ to take advantage of math.h support, be sure that the new C++ code compiles correctly before synthesizing with Vitis HLS. For example, if sqrtf() is used in the code with math.h, it requires the following code extern added to the C++ code to support it:


#include <math.h>
extern ā€œCā€ float sqrtf(float);

To avoid unnecessary hardware caused by type conversion, follow the warnings on mixing double and float types discussed in Floats and Doubles.