6.5.2 Double precision

For the rules used by the text interpreter for recognising double-precision integers, see Literals.

A double precision number is represented by a cell pair, with the most significant cell at the top-of-stack (TOS). It is trivial to convert an unsigned single to a double: simply push a 0 onto the TOS. Numbers are represented by Gforth using 2’s complement arithmetic, so converting a signed single to a (signed) double requires sign-extension across the most significant cell. This can be achieved using s>d. You cannot convert a number from single-cell to double-cell without knowing whether it represents an unsigned or a signed number. By contrast, in 2’s complement arithmetic the conversion from double to single just drops the most significant cell, and d>s just documents the intent.

D+ and d- are defined for signed operands, but also work for unsigned numbers.

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”