4.4 Rounding Modes

A complex rounding mode is of the form MPC_RNDxy where x and y are one of N (to nearest), Z (towards zero), U (towards plus infinity), D (towards minus infinity). The first letter refers to the rounding mode for the real part, and the second one for the imaginary part. For example MPC_RNDZU indicates to round the real part towards zero, and the imaginary part towards plus infinity.

The ‘round to nearest’ mode works as in the IEEE P754 standard: in case the number to be rounded lies exactly in the middle of two representable numbers, it is rounded to the one with the least significant bit set to zero. For example, the number 5, which is represented by (101) in binary, is rounded to (100)=4 with a precision of two bits, and not to (110)=6.

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