Unsigned arithmetic operator

Here is an example that uses an arithmetic operator on unsigned numbers. 

Equality operators are modeled similar to arithmetic operators in terms of whether signed or unsigned comparison is to be made. Here is an example that uses signed numbers. Note that in this case, the operands of the equality operator are of integer type because values of this type represent signed numbers. 

The arithmetic expression is parsed in order to retrieve its operator and the corresponding operands. In this example, it is -t operator. Now we have to check if the operands can evaluate to such values that when are added to each other they cause an overflow. The corresponding code is shown in lines 1595-1598 in the above image. Note that the operands, which may be complex expressions, are stored into variables of type type and it is ensured that the inserted code does not raise the overflow alarm itself. The code generated for this category of alarm can vary based on the arithmetic operator (i.e., whether it is + or - etc.), whether it is signed or unsigned arithmetic and whether the overflow is w.r.t. minimum and/or maximum bound. 

Example 10.1 shows the mechanism by which the predefined arithmetic operation, in VHDL is mapped to DesignWare components. The operation in the VHDL code for data type unsigned operands is mapped to the corresponding function in the std Jogic arith package. This function in turn calls the function mult which is mapped to the DesignWare synthetic operator MULT UNS OP. 

C has a cavalier attitude toward operations involving different numeric types. It allows you to perform mixed operations involving any of the numeric types, such as adding a character to a floating-point value. There is a standard set of rules, called the usual arithmetic conversions, that specifies how operations will be performed when the operands are of different types. Without going into detail, the usual arithmetic conversions typically direct that when two operands have a different precision, the less precise operand is promoted to match the more precise operand, and signed types are (when necessary) converted to unsigned. 

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