Re: [PATCH v9 2/9] lib: vsprintf: export simple_strntoull() in a safe prototype

[David Laight]

On Fri, 27 Mar 2026 12:57:56 +0200
Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx> wrote:

> On Fri, Mar 27, 2026 at 10:44:40AM +0000, David Laight wrote:
,,,
> > > but also wants to have the fraction part be limited in some cases to s32
> > > or so:
> > > 
> > > 	struct float
> > > 	{
> > > 		s64 integer;
> > > 		s32 fraction; // precision may be lost if input is longer
> > > 	}  
> > 
> > Are those 'fraction' counts of (say) 10^-6 (like times in seconds+usecs)
> > or true binary values where the value could be treated as a u64 (or u128)
> > for addition and subtraction.  
> 
> It depends. IIO has scale on top of that, so the fraction part can be 10⁻³,
> 10⁻⁶, 10⁻⁹. I don't remember by heart if the ABI requires all digits to be
> placed, I think we don't require that.

Seems like you want this function (untested):
u64 strtofrac(const char *buf, const char **end, unsigned int len)
{
	u64 val = 0;
	unsigned int digit;

	while (len--) {
		digit = *buf - '0';
		if (digit <= 9) {
			buf++;
			val += digit;
		}
		val *= 10;
	}
	while (*buf - '0' <= 9u)
		buf++;
	*end = buf;
	return val;
}

	David