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David
David

Reputation: 2190

Irregularities in Gforth's conversion to doubles

I'm fairly confused about how the s>d and d>s functions work in Forth.

From what I've read, typing 16.0 will put 160 0 on the stack (since it takes up two cells) and d. will show 160.

Now, if I enter 16 s>d I would expect the stack to be 160 0 and d. to show 160 like in the previous example. However, the stack is 16 0 and d. is 16.

Am I entering doubles incorrectly? Is s>d not as simple as "convert a single celled value into a double celled value? Is there any reason for this irregularity? Any clues would be much appreciated.

Upvotes: 0

Views: 101

Answers (1)

Lars Brinkhoff
Lars Brinkhoff

Reputation: 14325

Gforth interpets all of these the same: 1.60, 16.0, and 160., i.e. 160 converted to a double number. Whereas 16 s>d converts 16 to a double number.

ANS Forth only mandates that when the text interpreter processes a number that is immediately followed by a decimal point and is not found as a definition name, the text interpreter shall convert it to a double-cell number. But Gforth goes beoynd that: http://www.complang.tuwien.ac.at/forth/gforth/Docs-html/Number-Conversion.html#Number-Conversion

Upvotes: 2

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