Freescale Semiconductor StarCore SC140 - Manual (Page 55)

DALU
SC140 DSP Core Reference Manual 2-23
2.2.2.6.2 Two’s Complement Rounding
When two’s complement rounding is selected by setting the rounding mode (RM) bit in the SR, all values
greater than or equal to one-half are rounded up, and all values less than one-half are rounded down.
Therefore, a small positive bias is introduced.
For no scaling, the higher portion (HP) of the register is bits 39:16; the low portion (LP) is bits 15:0. The
HP is incremented by one bit if the LP was
≥ 1/2. The HP is left alone if the LP was <1/2. After rounding,
the LP is cleared. If scaling down is selected, the HP is bits 39:17 and the LP is bits 16:0. If scaling up is
selected, the HP is bits 39:15 and LP is bits 14:0.