| Add Proposal | Add Analysis | Edit Class, Environment, or Release |
| Number | 638
|
| Category | pending
|
| Synopsis | erratum/282: PROPOSAL - 4.5 sign and size rules
|
| State | open
|
| Class | errata-simple
|
| Arrival-Date | Nov 28 2004
|
| Originator | Steven Sharp <sharp@cadence.com>
|
| Release |
|
| Description |
Proposal for expression signedness and sizing issues Commentary: This is a stab at clarifying the description of how context-determined signedness and expression sizing works (a variety of errata). It also covers how reals work (erratum 83), and the special behavior of compares. It may not be adequate to resolve the issues, but it is an attempt. It was done in a hurry, so there may be problems with it. Insert more disclaimers here. The new text refers to a "primary" from the grammar. For some reason, "primary" does not include a string. Instead, strings are listed separately as expressions. This is apparently an error in the grammar, since it prevents the use of unary operators on strings, which should be legal. The new text assumes that this will be fixed; otherwise it needs to say "primary or string". Changes: In 4.5.2, CHANGE: -- Coerce the type of each operand of the expression (excepting those which are self-determined) to the type of the expression. -- Extend the size of each operand (excepting those which are self-determined) to the size of the expression. Perform sign extension if and only if the operand type (after type coercion) is signed. TO: -- Propagate the type and size of the expression (or self-determined sub- expression) back down to the context-determined operands of the expression. In general, any context-determined operand of an operator is the same type and size as the result of the operator. However, there are two exceptions: - If the result type of the operator is real, and it has a context- determined operand that is not real, that operand is treated as if it were self-determined and then converted to real just before the operator is applied. - The relational and equality operators have operands that are neither fully self-determined or context-determined. The operands affect each other as if they were context-determined operands with a result type and size (maximum of the two operand sizes) determined from them. However, the actual result type is always 1 bit unsigned. The type and size of the operands is independent of the rest of the expression and vice-versa. -- When propagation reaches a simple operand as defined in 4.2 (a primary as defined in A.8.4), then that operand is converted to the propagated type and size. If the operand must be extended, then it is sign-extended only if the propagated type is signed. |
| Fix |
Unknown |
Hosted by Boyd Technology