Re: [PATCH v12 02/11] lib: kstrtox: add kstrtoudec64() and kstrtodec64()

[Rodrigo Alencar]

On 26/05/15 08:21PM, David Laight wrote:
> On Fri, 15 May 2026 17:05:06 +0100
> Rodrigo Alencar <455.rodrigo.alencar@xxxxxxxxx> wrote:
> 
> > On 26/05/13 10:41AM, Rodrigo Alencar wrote:
> > > On 26/05/10 01:42PM, Rodrigo Alencar via B4 Relay wrote:  
> > > > From: Rodrigo Alencar <rodrigo.alencar@xxxxxxxxxx>
> > > > 
> > > > Add helpers that parses decimal numbers into 64-bit number, i.e., decimal
> > > > point numbers with pre-defined scale are parsed into a 64-bit value (fixed
> > > > precision). After the decimal point, digits beyond the specified scale
> > > > are ignored.  
> > > 
> > > Hi Andy,
> > > 
> > > I am starting over here, the other conversation is getting hard to follow.
> > > This is my new proposal...  
> > 
> > +cc David
> 
> I just wouldn't do it this way :-)
> 
> You end up with more code than you would get if you just converted the digits.

I am not sure about having more code, most of it is reused. The rest is input
validation and scaling.

...

> > > This function now becomes:
> > > 
> > > 	static int _kstrtoudec64(const char *s, unsigned int scale, u64 *res)
> > > 	{
> > > 		u64 _res = 0;
> > > 		unsigned int rv_int, rv_frac;
> > > 

integer part is parsed here:

> > > 		rv_int = _parse_integer(s, 10, &_res);
> > > 		if (rv_int & KSTRTOX_OVERFLOW)
> > > 			return -ERANGE;
> > > 		s += rv_int;
> > > 
> > > 		if (*s == '.')
> > > 			s++; /* skip decimal point */
> > > 

fractional part is parsed here:
(combined into the result so we can just skip the decimal point)

> > > 		rv_frac = _parse_integer_limit_init(s, 10, _res, &_res, scale);
> > > 		if (rv_frac & KSTRTOX_OVERFLOW)
> > > 			return -ERANGE;
> > > 		s += rv_frac;
> > > 

input validation on the presence of digits:
(similar to checking rv in _kstrtoull())

> > > 		if (!rv_int && !rv_frac && !isdigit(*s))
> > > 			return -EINVAL; /* no digits at all */
> > > 
> > > 		while (isdigit(*s)) /* truncate digits */
> > > 			s++;
> > > 

termination requirement:

> > > 		if (*s == '\n')
> > > 			s++;
> > > 		if (*s)
> > > 			return -EINVAL;
> > > 

result is scaled according to (scale - rv_frac):

> > > 		if (_res && (scale > (19 + rv_frac) || /* log10(2^64) = 19.26 */
> > > 		    check_mul_overflow(_res, int_pow(10, scale - rv_frac), &_res)))
> > > 			return -ERANGE;
> > > 
> > > 		*res = _res;
> > > 		return 0;
> > > 	}
> > > 

That above looks straightforward to me and the tests in the next patch are thorough.

...

> > I have a v13 ready with this. I'll give it a go soon...
> > 
> 

-- 
Kind regards,

Rodrigo Alencar