Subj : Re: Class width SpiderMonkey
To   : Jan Herling <JanHerling@t-online.de>
From : Brendan Eich <brendan@meer.net>
Date : Thu Nov 06 2003 10:15 am

Jan Herling wrote:

>Here is the important part of my Spidermonkey-Class:
>
>JSBool ClassASetValue(JSContext *cx, JSObject *obj, double value)
>{
>    jsval val;
>    JS_NewDoubleValue(cx, (jsdouble) value, &val);
>    JS_SetProperty(cx, obj, "a", &val);
>    ....
>}
>
>
>JSBool ClassAGetValue(JSContext *cx, JSObject *obj, float *value)
>{
>    jsval val;
>    jsdouble jsd;
>    .......
>    JS_GetProperty(cx, obj, "a", &val);
>    jsd = *JSVAL_TO_DOUBLE(val);                             ("or")
>JS_ValueToNumber(cx, val, &jsd);        (makes no differents - allways
>breaks down here if : "ca.a = 1" )
>    *value = (float) jsd;
>    .......
>}
>
>I think this is a problem with the conversion from JSVAL to DOUBLE.
>Is this a well known problem or bug?
>Or did I make a big mistake?
>  
>

You made a mistake.  Two, actually:

1.  In ClassASetValue, use JS_NewNumberValue, not JS_NewDoubleValue.  
Let the engine optimize 0 and 1 storage.

2.  You cannot assume that JSVAL_IS_DOUBLE(val) before calling 
JSVAL_TO_DOUBLE.  Use JS_ValueToNumber.

If you still have problems after fixing these, please send or post 
complete code and say exactly how it fails.

/be

.