Subj : sm: JS_ValueToInt unexpected results
To   : netscape.public.mozilla.jseng
From : Jens Thiele
Date : Sat Jan 08 2005 12:46 pm

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Hi,

JS_ValueToInt32 gives unexpected results (wrap around => negative) for
Number values:
[2147483647.5, 2147483648[

This is since the rounding is done after the range check:
js_ValueToInt32(JSContext *cx, jsval v, int32 *ip)
{
    jsdouble d;
    JSString *str;

    if (JSVAL_IS_INT(v)) {
        *ip = JSVAL_TO_INT(v);
        return JS_TRUE;
    }
    if (!js_ValueToNumber(cx, v, &d))
        return JS_FALSE;
    if (JSDOUBLE_IS_NaN(d) || d <= -2147483649.0 || 2147483648.0 <= d) {
        str = js_DecompileValueGenerator(cx, JSDVG_SEARCH_STACK, v, NULL);
        if (str) {
            JS_ReportErrorNumber(cx, js_GetErrorMessage, NULL,
                                 JSMSG_CANT_CONVERT,
JS_GetStringBytes(str));

        }
        return JS_FALSE;
    }
    *ip = (int32)floor(d + 0.5);     /* Round to nearest */
    return JS_TRUE;
}

Jens

attached a test case

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Content-Type: text/x-csrc;
 name="test.c"
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Content-Disposition: inline;
 filename="test.c"

/* get SpiderMonkey API declarations */
#include <jsapi.h>
/* EXIT_FAILURE and EXIT_SUCCESS */
#include <stdlib.h>  
/* strlen */
#include <string.h>

int
main(int argc, char** argv)
{
  /* pointer to our runtime object */
  JSRuntime *runtime=NULL;
  /* pointer to our context */
  JSContext *context=NULL;
  /* pointer to our global JavaScript object */
  JSObject  *global=NULL;

  /* script to run (should preduce an error) */
  char *script="2147483647.5";
  /* JavaScript value to store the result of the script */
  jsval rval;
  
  /* create new runtime, new context, global object */
  if (    (!(runtime = JS_NewRuntime (1024L*1024L)))
       || (!(context = JS_NewContext (runtime, 8192)))
       || (!(global  = JS_NewObject  (context, NULL, NULL, NULL)))
     ) return EXIT_FAILURE;
  /* set global object of context and initialize standard ECMAScript
     objects (Math, Date, ...) within this global object scope */
  if (!JS_InitStandardClasses(context, global)) return EXIT_FAILURE;

  /* now we are ready to run our script */
  if (JS_EvaluateScript(context, global,script, strlen(script),
			 "script", 1, &rval))
    return EXIT_FAILURE;
  /* clean up */
  JS_DestroyContext(context);
  JS_DestroyRuntime(runtime);
  JS_ShutDown();
  return EXIT_SUCCESS;
}

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