Libzita-alsa-pcmi is a C++ library for using ALSA audio devices with
minimal latency and using ALSA's memory-mapped mode (as used by Jack).
It hides most of the complexity of configuring and using ALSA devices
in this way.

Input and output audio streams are converted to / from 32-bit float-
ing point format, regardless of the hardware sample format. By cal-
ling the read and write functions from a real-time thread, it is ea-
sy to provide a callback interface, and to write applications that
work with both ALSA and Jack using the same processing code.

See jaaa or japa for examples.