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Sign Extension of SystemC Data Types
====================================
This document describes how sign extension is done for SystemC data types. This
includes implicit use of those data types, as well as methods like to_int()
The Proof Of Concept simulator is configured to use the following rules:
* Values that are smaller than a required width will be sign extended to the proper width.
* Signed values will "sign extend" the upper bit of the value to extend to the proper width.
* Unsigned values will "zero extend" a zero bit to extend to the proper width.
These values are signed:
sc_bigint
sc_signed
sc_int
sc_int_base
C++ signed integer types, e.g., int, long long
These values are unsigned (includes all the SystemC bit vector types):
sc_biguint
sc_unsigned
sc_uint
sc_uint_base
sc_bv
sc_bv_base
sc_lv
sc_lv_base
sc_signed_subref
sc_signed_subref_r
sc_unsigned_subref
sc_unsigned_subref_r
sc_int_subref
sc_int_subref_r
sc_uint_subref
sc_uint_subref_r
C++ unsigned integer types, e.g., unsigned int, unsigned long
These types are bool:
sc_signed_bitref
sc_signed_bitref_r
sc_unsigned_bitref
sc_unsigned_bitref_r
sc_int_bitref
sc_int_bitref_r
sc_uint_bitref
sc_uint_bitref_r
C++ bool type
The sign extension rules are enforced for the to_XXXX methods associated with
the various SystemC types:
to_int()
to_uint()
to_long()
to_ulong()
to_int64()
to_uint64()
Signed SystemC datatypes will sign extend their values when creating the return
type for these methods, For instance, given:
sc_int<10> x;
unsigned int j;
. . .
j = x.to_uint();
x will be sign extended using its upper bit to a width of 32 bits, and that
value assigned to j.
Similarly, to_long for an unsigned type like sc_biguint<12> will be zero
extended to the width of a C++ long, and that value returned.
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