This port of the MicroC RTOS for the PIC18 processor is an extension of an existing port by Nathan Brown and can be found here.
The extension of Nathan Brown's port is to save and restore the tmpdata and MATH_DATA sections during a context switch. The tmpdata and MATH_DATA sections are important for floating point and even some integer operations. According to the MPLAB C18 users guide, the tmpdata section contains compiler temporary variables for the non-interrupt service routine source and the MATH_DATA section contains arguments, return values, and temporary locations used by math library functions.
Download MicroC port for PIC18
Documentation of changes