Messages in this thread | | | From | David Laight <> | Subject | RE: [PATCH v4 1/3] math.h: add DIV_ROUND_UP_NO_OVERFLOW | Date | Tue, 24 Oct 2023 16:26:55 +0000 |
| |
From: Sebastian Reichel > Sent: 24 October 2023 17:18 > > Add a new DIV_ROUND_UP helper, which cannot overflow when > big numbers are being used.
For non-zero you can use (n - 1)/d + 1 instead of (n + d - 1)/d So maybe add: #define DIV_ROUND_UP_NON_ZERO(n, d) (((n) - 1)/(d) + 1)
Saves the compiler having to get the remainder (if not generated by a divide instruction.
David
> > Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com> > --- > include/linux/math.h | 11 +++++++++++ > 1 file changed, 11 insertions(+) > > diff --git a/include/linux/math.h b/include/linux/math.h > index dd4152711de7..f80bfb375ab9 100644 > --- a/include/linux/math.h > +++ b/include/linux/math.h > @@ -36,6 +36,17 @@ > > #define DIV_ROUND_UP __KERNEL_DIV_ROUND_UP > > +/** > + * DIV_ROUND_UP_NO_OVERFLOW - divide two numbers and always round up > + * @n: numerator / dividend > + * @d: denominator / divisor > + * > + * This functions does the same as DIV_ROUND_UP, but internally uses a > + * division and a modulo operation instead of math tricks. This way it > + * avoids overflowing when handling big numbers. > + */ > +#define DIV_ROUND_UP_NO_OVERFLOW(n, d) (((n) / (d)) + !!((n) % (d))) > + > #define DIV_ROUND_DOWN_ULL(ll, d) \ > ({ unsigned long long _tmp = (ll); do_div(_tmp, d); _tmp; }) > > -- > 2.42.0
- Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
| |