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linux/bitfield.h: import <linux/bitfield.h> from Linux 4.13

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Copied from Linux 4.13.

Commit log of 3e9b3112ec74 of Linux explains well why this header
is useful.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
This commit is contained in:
Masahiro Yamada 2017-09-29 10:35:17 +09:00 committed by Tom Rini
parent c898cba41e
commit 6990e91f09
1 changed files with 106 additions and 0 deletions
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106
include/linux/bitfield.h Normal file
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/*
* Copyright (C) 2014 Felix Fietkau <nbd@nbd.name>
* Copyright (C) 2004 - 2009 Ivo van Doorn <IvDoorn@gmail.com>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2
* as published by the Free Software Foundation
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*/
#ifndef _LINUX_BITFIELD_H
#define _LINUX_BITFIELD_H
#include <linux/bug.h>
/*
* Bitfield access macros
*
* FIELD_{GET,PREP} macros take as first parameter shifted mask
* from which they extract the base mask and shift amount.
* Mask must be a compilation time constant.
*
* Example:
*
* #define REG_FIELD_A GENMASK(6, 0)
* #define REG_FIELD_B BIT(7)
* #define REG_FIELD_C GENMASK(15, 8)
* #define REG_FIELD_D GENMASK(31, 16)
*
* Get:
* a = FIELD_GET(REG_FIELD_A, reg);
* b = FIELD_GET(REG_FIELD_B, reg);
*
* Set:
* reg = FIELD_PREP(REG_FIELD_A, 1) |
* FIELD_PREP(REG_FIELD_B, 0) |
* FIELD_PREP(REG_FIELD_C, c) |
* FIELD_PREP(REG_FIELD_D, 0x40);
*
* Modify:
* reg &= ~REG_FIELD_C;
* reg |= FIELD_PREP(REG_FIELD_C, c);
*/
#define __bf_shf(x) (__builtin_ffsll(x) - 1)
#define __BF_FIELD_CHECK(_mask, _reg, _val, _pfx) \
({ \
BUILD_BUG_ON_MSG(!__builtin_constant_p(_mask), \
_pfx "mask is not constant"); \
BUILD_BUG_ON_MSG(!(_mask), _pfx "mask is zero"); \
BUILD_BUG_ON_MSG(__builtin_constant_p(_val) ? \
~((_mask) >> __bf_shf(_mask)) & (_val) : 0, \
_pfx "value too large for the field"); \
BUILD_BUG_ON_MSG((_mask) > (typeof(_reg))~0ull, \
_pfx "type of reg too small for mask"); \
__BUILD_BUG_ON_NOT_POWER_OF_2((_mask) + \
(1ULL << __bf_shf(_mask))); \
})
/**
* FIELD_FIT() - check if value fits in the field
* @_mask: shifted mask defining the field's length and position
* @_val: value to test against the field
*
* Return: true if @_val can fit inside @_mask, false if @_val is too big.
*/
#define FIELD_FIT(_mask, _val) \
({ \
__BF_FIELD_CHECK(_mask, 0ULL, _val, "FIELD_FIT: "); \
!((((typeof(_mask))_val) << __bf_shf(_mask)) & ~(_mask)); \
})
/**
* FIELD_PREP() - prepare a bitfield element
* @_mask: shifted mask defining the field's length and position
* @_val: value to put in the field
*
* FIELD_PREP() masks and shifts up the value. The result should
* be combined with other fields of the bitfield using logical OR.
*/
#define FIELD_PREP(_mask, _val) \
({ \
__BF_FIELD_CHECK(_mask, 0ULL, _val, "FIELD_PREP: "); \
((typeof(_mask))(_val) << __bf_shf(_mask)) & (_mask); \
})
/**
* FIELD_GET() - extract a bitfield element
* @_mask: shifted mask defining the field's length and position
* @_reg: 32bit value of entire bitfield
*
* FIELD_GET() extracts the field specified by @_mask from the
* bitfield passed in as @_reg by masking and shifting it down.
*/
#define FIELD_GET(_mask, _reg) \
({ \
__BF_FIELD_CHECK(_mask, _reg, 0U, "FIELD_GET: "); \
(typeof(_mask))(((_reg) & (_mask)) >> __bf_shf(_mask)); \
})
#endif