The MASS libraries consist of a library of scalar functions, described in Using the scalar library; and a set of vector libraries tuned for specific architectures, described in Using the vector libraries. The functions contained in both scalar and vector libraries are automatically called at certain levels of optimization, but you can also call them explicitly in your programs. Note that the accuracy and exception handling might not be identical in MASS functions and system library functions.
Compiling and linking a program with MASS describes how to compile and link a program that uses the MASS libraries, and how to selectively use the MASS scalar library functions in concert with the regular libm.a scalar functions.