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#### 5.5.2 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+`       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”
```

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