On 14/01/2013 15:52, Jonas Maebe wrote:
On 14 Jan 2013, at 16:44, Martin wrote:
This is casting a "set of bits" (neither signed, nor unsigned - a set
is not a number at all) into a number. This only needs to have a
definition, if it should cast to signed or unsigned type.
It has to be signed, because otherwise any negative number in the
operation would trigger a range check error when it gets converted to
a (larger) unsigned type. The nature of the operation that is used
afterwards is irrelevant, range checking always operates in exactly
the same way when performing a type conversion from one type to
another. This is required to have predictable behaviour in a
programming language.
not sure if I follow. If "or" performs on a "set of bits" (rather than a
number), and a set (not being a number) is neither signed or unsigned,
then before the "OR" both operands (independent of being signed or not)
will be cast to a set. The result is a set. The set can be converted to
either signed or unsigned. The set has no range checking.
result := bit_set32(a) or bit_set32(b)
If result has also 32 (or more) bits, then no range check error can
occur. In the set, the high-bit has no meaning. It is neither part of
the (unsigned positive) numer, nor is it sign indicator. This meaning is
only applied by casting it to a numeric type.
Same as
var i: set of (b0, b1, b2 .... b31);
signed := integer(i);
unsigned := cardinal(i);
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