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| Number | 83
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| Category | errata
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| Synopsis | 4.5: Expression type/evaluation issues with real operands
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| State | open
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| Class | errata-discuss
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| Arrival-Date | Jul 30 2002
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| Originator | Dennis Marsa
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| Release | 2001b: 4.5
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| Description |
1) Section 4.5.1 includes the following text in the rules for determining the result type of an expression: "Reals converted to integers by type coercion are signed" Does the above statement belong here? According to Section 3.9.2, a real is converted to integer only when a real result is assigned to an integer variable. But an assignment is not an expression, and the type of the LHS of an assignment does not effect how the RHS expression is processed. Reals can be explicitly converted to an integer value by using either the $rtoi or $realtobits system functions. However, the result type of those functions are defined to be "integer" and "[63:0]", respectively, and the rules for handling operands of those types ar already defined by the other statements in section 4.5.1. 2) Section 4.5.1 also includes the following statement: "For non-self-determined operands the following rules apply: if any operand is real the result is real;" Taking this statement together with the rules for evaluating an expression from section 4.5.2 would seem to indicate that the expression: (1 / 2) + 0.0 should evaluate to 0.5, because one operand (0.0) being real, would force all non-self-determined operands to be converted to real before the expression is evaluated. Thus, after type conversion, we would have: (1.0 / 2.0) + 0.0 which would yield a result of 0.5. Is this the correct interpretation of how real operands should be handled? Verilog-XL, NC-Verilog and MTI all currently evaluate the above expression to 0.0. 3) Section 4.5.2 contains the statement: "Determine the sign of the expression using the rules outlined in 4.5.1." It be better for the word "sign" to be changed to "type", so that the statement reads: "Determine the type of the expression usiing the rules outlined in 4.5.1." 4) The title of section 4.5 is "Signed Expressions" though it really discusses how to determine the type of, and evaluate, an expression. Perhaps a better title would be something like: "Expression Type Determination and Evaluation" or maybe just: "Expression Evaluation" |
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