[sv-ec] RE: Enum type as associative array index type (7.8.6)

I could make an argument for either way.

By the way, 7.4.6 says,

If an index expression is out of bounds or if any bit in the index expression is x or z, then the index shall be invalid. Reading from an unpacked array of any kind with an invalid index shall return the value specified in Table 7-1. Writing to an array with an invalid index shall perform no operation, with the exceptions of writing to element [$+1] of a queue (described in 7.10.1) and creating a new element of an associative array (described in 7.8.6). Implementations may issue a warning if an invalid index occurs for a read or write operation on an array.

and 7.8.6 says,

7.8.6 Accessing invalid indices
If a read operation uses an index that is a 4-state expression with one or more x or z bits, or an attempt is made to read a nonexistent entry, then a warning shall be issued and the nonexistent entry value for the array type shall be returned, as shown in Table 7-1 (see 7.4.6). A user-specified default shall not issue a warning and returns the value specified in 7.9.11.
If an invalid index is used during a write operation, the write shall be ignored, and a warning shall be issued.

The two sections seem to be using the term 'invalid' with different meanings. Specifically, in 7.4.6 an index is invalid if it is out of bounds, whereas that is not included in the definition in 7.8.6. The reference in 7.4.6 to creating a new element of an associative array should probably be to 7.8.7 instead of 7.8.6.

Shalom

From: owner-sv-ec@eda.org [mailto:owner-sv-ec@eda.org] On Behalf Of Brad Pierce
Sent: Sunday, March 23, 2014 01:37
To: sv-ec@eda.org
Subject: [sv-ec] Enum type as associative array index type (7.8.6)

As discussed in http://www.eda.org/svdb/view.php?id=4510 , if an enum variable has been assigned a value outside the enumeration set, and it is used as the index when writing to an associative array, is the write ignored as an "invalid index" in 7.8.6? For example,

module test;
typedef enum {A, B, C} ET;
bit assoc[ET];
initial begin
assoc[ET'(100)] = 1'b1;
$display(assoc.exists(ET'(100)));
end
endmodule

-- Brad

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