linux-kernel - Re: [RFC PATCH v4 2/8] math64: add rem

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Date: Fri, 31 May 2024 07:04:42 -0700
From: "Darrick J. Wong" <djwong@...nel.org>
To: Zhang Yi <yi.zhang@...weicloud.com>
Cc: linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, hch@...radead.org, brauner@...nel.org,
	david@...morbit.com, chandanbabu@...nel.org, jack@...e.cz,
	willy@...radead.org, yi.zhang@...wei.com, chengzhihao1@...wei.com,
	yukuai3@...wei.com
Subject: Re: [RFC PATCH v4 2/8] math64: add rem_u64() to just return the
 remainder

On Wed, May 29, 2024 at 05:52:00PM +0800, Zhang Yi wrote:
> From: Zhang Yi <yi.zhang@...wei.com>
> 
> Add a new helper rem_u64() to only get the remainder of unsigned 64bit
> divide with 32bit divisor.
> 
> Signed-off-by: Zhang Yi <yi.zhang@...wei.com>

Modulo hch's comments,
Reviewed-by: Darrick J. Wong <djwong@...nel.org>

--D

> ---
>  include/linux/math64.h | 24 ++++++++++++++++++++++++
>  1 file changed, 24 insertions(+)
> 
> diff --git a/include/linux/math64.h b/include/linux/math64.h
> index d34def7f9a8c..618df4862091 100644
> --- a/include/linux/math64.h
> +++ b/include/linux/math64.h
> @@ -3,6 +3,7 @@
>  #define _LINUX_MATH64_H
>  
>  #include <linux/types.h>
> +#include <linux/log2.h>
>  #include <linux/math.h>
>  #include <asm/div64.h>
>  #include <vdso/math64.h>
> @@ -12,6 +13,20 @@
>  #define div64_long(x, y) div64_s64((x), (y))
>  #define div64_ul(x, y)   div64_u64((x), (y))
>  
> +/**
> + * rem_u64 - remainder of unsigned 64bit divide with 32bit divisor
> + * @dividend: unsigned 64bit dividend
> + * @divisor: unsigned 32bit divisor
> + *
> + * Return: dividend % divisor
> + */
> +static inline u32 rem_u64(u64 dividend, u32 divisor)
> +{
> +	if (is_power_of_2(divisor))
> +		return dividend & (divisor - 1);
> +	return dividend % divisor;
> +}
> +
>  /**
>   * div_u64_rem - unsigned 64bit divide with 32bit divisor with remainder
>   * @dividend: unsigned 64bit dividend
> @@ -86,6 +101,15 @@ static inline s64 div64_s64(s64 dividend, s64 divisor)
>  #define div64_long(x, y) div_s64((x), (y))
>  #define div64_ul(x, y)   div_u64((x), (y))
>  
> +#ifndef rem_u64
> +static inline u32 rem_u64(u64 dividend, u32 divisor)
> +{
> +	if (is_power_of_2(divisor))
> +		return dividend & (divisor - 1);
> +	return do_div(dividend, divisor);
> +}
> +#endif
> +
>  #ifndef div_u64_rem
>  static inline u64 div_u64_rem(u64 dividend, u32 divisor, u32 *remainder)
>  {
> -- 
> 2.39.2
> 
>