Node:Double precision, Next:Bitwise operations, Previous:Single precision, Up:Arithmetic
For the rules used by the text interpreter for recognising double-precision integers, see 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: d+, d-.
s>d n -- d core ``s-to-d''
d>s d -- n double ``d-to-s''
d+ d1 d2 -- d double ``d-plus''
d- d1 d2 -- d double ``d-minus''
dnegate d1 -- d2 double ``d-negate''
dabs d -- ud double ``d-abs''
dmin d1 d2 -- d double ``d-min''
dmax d1 d2 -- d double ``d-max''