linux-kernel - Re: [PATCH 11/16] byteorder: provide a linux/byteorder.h with {be,le}_to_cpu() and cpu_to

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Date:	Tue, 27 May 2014 17:44:29 -0700
From:	Joe Perches <joe@...ches.com>
To:	Cody P Schafer <dev@...yps.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Linux PPC <linuxppc-dev@...ts.ozlabs.org>,
	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
Subject: Re: [PATCH 11/16] byteorder: provide a linux/byteorder.h with
 {be,le}_to_cpu() and cpu_to_{be,le}() macros

On Tue, 2014-05-27 at 17:22 -0700, Cody P Schafer wrote:
> Rather manually specifying the size of the integer to be converted, key
> off of the type size. Reduces duplicate size info and the occurance of
> certain types of bugs (using the wrong sized conversion).
[]
> diff --git a/include/linux/byteorder.h b/include/linux/byteorder.h
[]
> @@ -0,0 +1,34 @@
> +#ifndef LINUX_BYTEORDER_H_
> +#define LINUX_BYTEORDER_H_
> +
> +#include <asm/byteorder.h>
> +
> +#define be_to_cpu(v) \
> +	__builtin_choose_expr(sizeof(v) == sizeof(uint8_t) , v,	\
> +	__builtin_choose_expr(sizeof(v) == sizeof(uint16_t), be16_to_cpu(v), \
> +	__builtin_choose_expr(sizeof(v) == sizeof(uint32_t), be32_to_cpu(v), \
> +	__builtin_choose_expr(sizeof(v) == sizeof(uint64_t), be64_to_cpu(v), \
> +		(void)0))))

probably better to use BUILD_BUG instead of these 0 returns

> +
> +#define le_to_cpu(v) \
> +	__builtin_choose_expr(sizeof(v) == sizeof(uint8_t) , v,	\
> +	__builtin_choose_expr(sizeof(v) == sizeof(uint16_t), le16_to_cpu(v), \
> +	__builtin_choose_expr(sizeof(v) == sizeof(uint32_t), le32_to_cpu(v), \
> +	__builtin_choose_expr(sizeof(v) == sizeof(uint64_t), le64_to_cpu(v), \
> +		(void)0))))
> +
> +#define cpu_to_le(v) \
> +	__builtin_choose_expr(sizeof(v) == sizeof(uint8_t) , v,	\
> +	__builtin_choose_expr(sizeof(v) == sizeof(uint16_t), cpu_to_le16(v), \
> +	__builtin_choose_expr(sizeof(v) == sizeof(uint32_t), cpu_to_le32(v), \
> +	__builtin_choose_expr(sizeof(v) == sizeof(uint64_t), cpu_to_le64(v), \
> +		(void)0))))
> +
> +#define cpu_to_be(v) \
> +	__builtin_choose_expr(sizeof(v) == sizeof(uint8_t) , v,	\
> +	__builtin_choose_expr(sizeof(v) == sizeof(uint16_t), cpu_to_be16(v), \
> +	__builtin_choose_expr(sizeof(v) == sizeof(uint32_t), cpu_to_be32(v), \
> +	__builtin_choose_expr(sizeof(v) == sizeof(uint64_t), cpu_to_be64(v), \
> +		(void)0))))
> +
> +#endif



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