6.5.2 Double precision

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+ ( ud1 ud2 – ud ) 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”