Re: [PATCH v15 03/12] lib: kstrtox: add kstrtoudec64() and kstrtodec64()

[Andy Shevchenko]

On Sun, May 31, 2026 at 09:30:46AM +0100, Rodrigo Alencar via B4 Relay wrote:
> 
> 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.

...

> +static int _kstrtoudec64(const char *s, unsigned int scale, u64 *res)
> +{
> +	u64 _res = 0;
> +	unsigned int rv_int, rv_frac;
> +
> +	rv_int = _parse_integer(s, 10, &_res);
> +	if (rv_int & KSTRTOX_OVERFLOW)
> +		return -ERANGE;
> +	s += rv_int;
> +
> +	if (*s == '.')
> +		s++; /* skip decimal point */
> +
> +	rv_frac = _parse_integer_limit_init(s, 10, _res, &_res, scale);
> +	if (rv_frac & KSTRTOX_OVERFLOW)
> +		return -ERANGE;
> +	s += rv_frac;

> +	if (!rv_int && !rv_frac && !isdigit(*s))

Do we care about isdigit() here? Why?

> +		return -EINVAL; /* no digits at all */

> +	while (isdigit(*s)) /* truncate digits */
> +		s++;

> +	if (*s == '\n')
> +		s++;
> +	if (*s)
> +		return -EINVAL;
> +
> +	if (_res && (scale > (19 + rv_frac) || /* log10(2^64) = 19.26 */

It's better to make comment closer to the operand

	if (_res && (scale > (19 + rv_frac) /* log10(2^64) = 19.26 */ ||

> +	    check_mul_overflow(_res, int_pow(10, scale - rv_frac), &_res)))

Can we deduplicate the scale - rv_frac?
I mean, would it be possible to do

	if (_res && ((scale - rv_frac) > 19 /* log10(2^64) = 19.26 */ ||

without possible wraparound?

> +		return -ERANGE;
> +
> +	*res = _res;
> +	return 0;
> +}

...

> +/**
> + * kstrtoudec64() - Convert a string to an unsigned 64-bit value that represents
> + *		    a scaled decimal number.
> + * @s: The start of the string. The string must be null-terminated, and may also
> + *  include a single newline before its terminating null. The first character
> + *  may also be a plus sign, but not a minus sign. Digits beyond the specified
> + *  scale are ignored.
> + * @scale: The number of digits to the right of the decimal point. For example,
> + *  a scale of 2 would mean the number is represented with two decimal places,
> + *  so "123.45" would be represented as 12345.
> + * @res: Where to write the result of the conversion on success.

I believe it's better to leave short descriptions short and describe the
examples and other considerations here, in the description section.

All the same for the second one below.

> + * Return: 0 on success, -ERANGE on overflow and -EINVAL on parsing error.
> + */

-- 
With Best Regards,
Andy Shevchenko