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For the rules used by the text interpreter for recognising double-precision integers, see 5.13.2 Number Conversion.
A double precision number is represented by a cell pair, with the most
significant cell at the TOS. It is trivial to convert an unsigned single
to a double: simply push a
0 onto the TOS. Since numbers are
represented by Gforth using 2's complement arithmetic, converting a
signed single to a (signed) double requires sign-extension across the
most significant cell. This can be achieved using
s>d. The moral
of the story is that you cannot convert a number without knowing whether
it represents an unsigned or a signed number.
These words are all defined for signed operands, but some of them also
work for unsigned numbers:
doc-s>d doc-d>s doc-d+ doc-d- doc-dnegate doc-dabs doc-dmin doc-dmax
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