Altera Nios II C2H Compiler - Manual (Page 44)

3–4 9.1 Altera Corporation
Nios II C2H Compiler User Guide November 2009
One-to-One C-to-Hardware Mapping
Pipelined Operations and Assignments
The C2H Compiler always registers the results of the operators listed in
Table 3–3 . Some arithmetic operations, such as multiplication, use a large
amount of logic, which creates a significant propagation delay through
the circuit. Calculating these operations in series with other operations in
a single clock cycle would incur unacceptable propagation delays and
significantly reduce the maximum achievable clock frequency (f
MAX
) for
the system. The C2H Compiler pipelines these operations by giving each
its own registered assignment. There are exceptions for cases in which an
operation reduces to trivial logic, as listed in
Table 3–3
The general rule "one registered assignment for every = operator" can be
amended to read, "one registered assignment for every = operator or
complex arithmetic operator".
Table 3–3. Complex Arithmetic Operations Pipelined by the C2H Compiler
Operator Description Exceptions
* Multiplication Either operand is a constant power of
2, which reduces to left-shift operation
/ Division Right-hand operand is a constant
power of 2, which reduces to a right-
shift operation
% Modulus Right-hand operand is a constant
power of 2, which reduces to a
masking operation
>> Right bit-wise shift Right-hand side is constant
<< Left bit-wise shift Right-hand side is constant