Re: Signed vs Unsigned Operators (Stavros Macrakis)
Thu, 2 Jul 1992 19:43:44 GMT

          From comp.compilers

Related articles
Signed vs Unsigned Operators (Elliot H. Mednick) (1992-07-02)
Re: Signed vs Unsigned Operators (1992-07-02)
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Newsgroups: comp.compilers
From: (Stavros Macrakis)
Organization: OSF Research Institute
Date: Thu, 2 Jul 1992 19:43:44 GMT
Keywords: types, syntax
References: 92-07-010

Mednick says:
      I am looking for references to languages where the operator, not the
      operands, determines if the operation should be signed or unsigned....

      In Verilog, there is a data type, called REG, that is unsigned (since it
      maps to real hardware registers). Therefore, arithmetic operations on
      that type are unsigned as well (i.e. multiplication, division, right
      shift, etc.).

Rather than adding signed/unsigned operators, why not think in terms of
type conversion? REG should probably be considered as of type
vector-of-bits, not as either signed or unsigned integer.

Common uses of REG might be signed integer (in one of a number of formats)
and unsigned integer, but there are others as well, such as floating-point
number (in one of a number of formats), vector of bytes, vector of BCD
digits, etc. Some bitwise operations (and, or, xor, ...) actually do
operate on vectors of bits.

So rather than have n(types) x n(operations) kinds of operator, why not
just have n(types) converter functions and n(operations) operations?

In your example, you'd say (for instance)

X = (sm) Y + (sm) Z.

This also permits expression format conversions and mixed-mode arithmetic
simply and consistently, e.g.

(tc) X = (sm) Y + (un) Z

where tc = two's complement, sm = sign-magnitude, un = unsigned


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