Since a few years no System z offers hardware support for decimal floating point operations as defined by IEEE 754-2008. This allows for exact and very fast calculations in the decimal (and not the normal binary) system in the processor.
You can check if your system does support this by
cat /proc/cpuinfo | grep features
features : esan3 zarch stfle msa ldisp eimm dfp edat etf3eh highgprs
If you see a "dfp" in included in the feature list, your system is enabled for decimal floating point.
The new instructions can be used from Java and C/C++. For Java use the java.math.BigDecimal class in a recent JVM. Other languages need compiler and library support and language extensions. ISO/IEC TR 24732 defines this for C and ISO/IEC TR 24733 for C++.
This updated whitepaper describes the details for what's needed to exploit this feature. It includes some performance results as well and all the necessary references