1 /*
2  * Copyright (C) 2014 Felix Fietkau <nbd@nbd.name>
3  * Copyright (C) 2004 - 2009 Ivo van Doorn <IvDoorn@gmail.com>
4  *
5  * This program is free software; you can redistribute it and/or modify
6  * it under the terms of the GNU General Public License version 2
7  * as published by the Free Software Foundation
8  *
9  * This program is distributed in the hope that it will be useful,
10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
12  * GNU General Public License for more details.
13  */
14 
15 #ifndef _LINUX_BITFIELD_H
16 #define _LINUX_BITFIELD_H
17 
18 #include <linux/build_bug.h>
19 #include <asm/byteorder.h>
20 
21 /*
22  * Bitfield access macros
23  *
24  * FIELD_{GET,PREP} macros take as first parameter shifted mask
25  * from which they extract the base mask and shift amount.
26  * Mask must be a compilation time constant.
27  *
28  * Example:
29  *
30  *  #define REG_FIELD_A  GENMASK(6, 0)
31  *  #define REG_FIELD_B  BIT(7)
32  *  #define REG_FIELD_C  GENMASK(15, 8)
33  *  #define REG_FIELD_D  GENMASK(31, 16)
34  *
35  * Get:
36  *  a = FIELD_GET(REG_FIELD_A, reg);
37  *  b = FIELD_GET(REG_FIELD_B, reg);
38  *
39  * Set:
40  *  reg = FIELD_PREP(REG_FIELD_A, 1) |
41  *	  FIELD_PREP(REG_FIELD_B, 0) |
42  *	  FIELD_PREP(REG_FIELD_C, c) |
43  *	  FIELD_PREP(REG_FIELD_D, 0x40);
44  *
45  * Modify:
46  *  reg &= ~REG_FIELD_C;
47  *  reg |= FIELD_PREP(REG_FIELD_C, c);
48  */
49 
50 #define __bf_shf(x) (__builtin_ffsll(x) - 1)
51 
52 #define __BF_FIELD_CHECK(_mask, _reg, _val, _pfx)			\
53 	({								\
54 		BUILD_BUG_ON_MSG(!__builtin_constant_p(_mask),		\
55 				 _pfx "mask is not constant");		\
56 		BUILD_BUG_ON_MSG((_mask) == 0, _pfx "mask is zero");	\
57 		BUILD_BUG_ON_MSG(__builtin_constant_p(_val) ?		\
58 				 ~((_mask) >> __bf_shf(_mask)) & (_val) : 0, \
59 				 _pfx "value too large for the field"); \
60 		BUILD_BUG_ON_MSG((_mask) > (typeof(_reg))~0ull,		\
61 				 _pfx "type of reg too small for mask"); \
62 		__BUILD_BUG_ON_NOT_POWER_OF_2((_mask) +			\
63 					      (1ULL << __bf_shf(_mask))); \
64 	})
65 
66 /**
67  * FIELD_FIT() - check if value fits in the field
68  * @_mask: shifted mask defining the field's length and position
69  * @_val:  value to test against the field
70  *
71  * Return: true if @_val can fit inside @_mask, false if @_val is too big.
72  */
73 #define FIELD_FIT(_mask, _val)						\
74 	({								\
75 		__BF_FIELD_CHECK(_mask, 0ULL, 0ULL, "FIELD_FIT: ");	\
76 		!((((typeof(_mask))_val) << __bf_shf(_mask)) & ~(_mask)); \
77 	})
78 
79 /**
80  * FIELD_PREP() - prepare a bitfield element
81  * @_mask: shifted mask defining the field's length and position
82  * @_val:  value to put in the field
83  *
84  * FIELD_PREP() masks and shifts up the value.  The result should
85  * be combined with other fields of the bitfield using logical OR.
86  */
87 #define FIELD_PREP(_mask, _val)						\
88 	({								\
89 		__BF_FIELD_CHECK(_mask, 0ULL, _val, "FIELD_PREP: ");	\
90 		((typeof(_mask))(_val) << __bf_shf(_mask)) & (_mask);	\
91 	})
92 
93 /**
94  * FIELD_GET() - extract a bitfield element
95  * @_mask: shifted mask defining the field's length and position
96  * @_reg:  value of entire bitfield
97  *
98  * FIELD_GET() extracts the field specified by @_mask from the
99  * bitfield passed in as @_reg by masking and shifting it down.
100  */
101 #define FIELD_GET(_mask, _reg)						\
102 	({								\
103 		__BF_FIELD_CHECK(_mask, _reg, 0U, "FIELD_GET: ");	\
104 		(typeof(_mask))(((_reg) & (_mask)) >> __bf_shf(_mask));	\
105 	})
106 
107 extern void __compiletime_error("value doesn't fit into mask")
108 __field_overflow(void);
109 extern void __compiletime_error("bad bitfield mask")
110 __bad_mask(void);
field_multiplier(u64 field)111 static __always_inline u64 field_multiplier(u64 field)
112 {
113 	if ((field | (field - 1)) & ((field | (field - 1)) + 1))
114 		__bad_mask();
115 	return field & -field;
116 }
field_mask(u64 field)117 static __always_inline u64 field_mask(u64 field)
118 {
119 	return field / field_multiplier(field);
120 }
121 #define ____MAKE_OP(type,base,to,from)					\
122 static __always_inline __##type type##_encode_bits(base v, base field)	\
123 {									\
124 	if (__builtin_constant_p(v) && (v & ~field_mask(field)))	\
125 		__field_overflow();					\
126 	return to((v & field_mask(field)) * field_multiplier(field));	\
127 }									\
128 static __always_inline __##type type##_replace_bits(__##type old,	\
129 					base val, base field)		\
130 {									\
131 	return (old & ~to(field)) | type##_encode_bits(val, field);	\
132 }									\
133 static __always_inline void type##p_replace_bits(__##type *p,		\
134 					base val, base field)		\
135 {									\
136 	*p = (*p & ~to(field)) | type##_encode_bits(val, field);	\
137 }									\
138 static __always_inline base type##_get_bits(__##type v, base field)	\
139 {									\
140 	return (from(v) & field)/field_multiplier(field);		\
141 }
142 #define __MAKE_OP(size)							\
143 	____MAKE_OP(le##size,u##size,cpu_to_le##size,le##size##_to_cpu)	\
144 	____MAKE_OP(be##size,u##size,cpu_to_be##size,be##size##_to_cpu)	\
145 	____MAKE_OP(u##size,u##size,,)
146 ____MAKE_OP(u8,u8,,)
147 __MAKE_OP(16)
148 __MAKE_OP(32)
149 __MAKE_OP(64)
150 #undef __MAKE_OP
151 #undef ____MAKE_OP
152 
153 #endif
154