BSV by Example - Computation Structures Group

Since a UInt#(n) is an unsigned int, you cannot initialize it with a negative number. The first line
in rule step0 is commented out in the code; uncomment it and you will get the error message:
Error: "Tb.bsv", line 40, column 19: (T0051)
Literal ‘-1’ is not a valid UInt#(16).
UInt#(n) does not allow access to individual bits, as such [ ] is not a legal construct for UInt#(n)
as it is for Bit#(n).
foo = foo & 5;
$display("foo[0] = %x", foo[0]); //invalid statement
foo = ’hffff;
$display("foo = %x", foo); //valid statement
// and it wraps just like you would expect it to
foo = foo + 1;
$display("foo = %x", foo);
Because this is an unsigned number, the value can never be less than zero. This display:
$display("fooneg = %x", foo < 0);
is displayed the same as:
$display("fooneg = %x", 1’d0 ) ;
One way to get min and max values from UInts is to use unpack:
UInt#(16) maxUInt16 = unpack(’1); // all ones
UInt#(16) minUInt16 = unpack(0);
The next rule, step1, examines the Int#(n) data type. Int#(n) has similar restrictions as UInt#(n),
but it does include negative numbers. Again, the quick way to get min and max values is use unpack:
Int#(16) maxInt16 = unpack({1’b0,’1}); // ’h011111
Int#(16) minInt16 = unpack({1’b1,’0}); // ’h100000
As with UInt#(n), you cannot perform bit manipulation directly. The following statement will give
an error:
$display("error1 = %x", minInt16[4]);
Because the type Int#(n) (as well as the type UInt#(n) is in the Arith type class, you can perform
the operations +, -, /, *, %. But be careful when using multiplication and division functions as
they may create long timing paths.
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