For all these functions there is one more argument compared to the fpmul function. This is the previous value of the accumulator.
v8float fpmac(v8float acc, v32float xbuf, int xstart, unsigned int xoffs, v8float zbuf, int zstart, unsigned int zoffs)
fpmac : multiply operands and add to the accumulator
fpmsc : multiply operands and subtract from the accumulator
fpmac_abs : multiply operands and add the absolute value to the accumulator
fpmsc_abs : multiply operands and subtract the absolute value from the accumulator
The two “abs” variants are available only for real arguments.