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## Re: [gforth] my vsum function is suspiciously non-local

 From: Carsten Strotmann (private) Subject: Re: [gforth] my vsum function is suspiciously non-local Date: Sun, 07 Mar 2010 19:20:09 +0100 User-agent: Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.6; en-GB; rv:1.9.1.8) Gecko/20100216 Thunderbird/3.0.2

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Hello Terence,

my solution would be:

: vsum ( addr u -- n )
CELLS      ( addr u      ) \ adjust u to size of cell
DO         ( 0            )
I        ( 0 i          ) \ i = index = address
@        ( 0 u          ) \ u = value of cell i
+        ( n            ) \ n = result
1        ( n 1          )
CELLS    ( n <c>        ) \ <c> = size of a cell in byte
\ this is architecture dep.
+LOOP      ( n            )
;            ( n            )

condensed:

: vsum ( addr u -- n ) CELLS OVER + SWAP  0 -ROT  DO  I @ +  1 CELLS +LOOP ;

No local variables needed.

- -- Carsten

On 3/7/10 6:53 PM, Terrence Brannon wrote:
> I used a "global variable" named tally to handle this tutorial
> assignment, but I think there must be a way to avoid the use of such a
> variable in solving this problem. Any help is appreciated:
>
> \    Assignment: Write a definition vsum ( addr u -- n ) that computes
> the sum of u cells, with the first of these cells at addr, the next
> one at addr cell+ etc.
>
> ( Usage:
>      create vx 2 , 2 , 2 , 2 , 2 ,
>      vx 5 vsum
> )
>
> : loop-range ( number-of-cells -- number-of-cells zero )  0 ;
> : get-value-at-address-offset ( address offset -- v ) cells + @ ;
> : increase-value ( n addr -- v+n ) TUCK @ + SWAP ! ;
> VARIABLE tally
> : vsum { address u }
>     u loop-range U+DO
>       tally increase-value
>     LOOP
>     tally @ ;
>
>

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