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 “C” 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.