xref: /linux/arch/x86/include/asm/div64.h (revision a1c613ae4c322ddd58d5a8539dbfba2a0380a8c0)
1 /* SPDX-License-Identifier: GPL-2.0 */
2 #ifndef _ASM_X86_DIV64_H
3 #define _ASM_X86_DIV64_H
4 
5 #ifdef CONFIG_X86_32
6 
7 #include <linux/types.h>
8 #include <linux/log2.h>
9 
10 /*
11  * do_div() is NOT a C function. It wants to return
12  * two values (the quotient and the remainder), but
13  * since that doesn't work very well in C, what it
14  * does is:
15  *
16  * - modifies the 64-bit dividend _in_place_
17  * - returns the 32-bit remainder
18  *
19  * This ends up being the most efficient "calling
20  * convention" on x86.
21  */
22 #define do_div(n, base)						\
23 ({								\
24 	unsigned long __upper, __low, __high, __mod, __base;	\
25 	__base = (base);					\
26 	if (__builtin_constant_p(__base) && is_power_of_2(__base)) { \
27 		__mod = n & (__base - 1);			\
28 		n >>= ilog2(__base);				\
29 	} else {						\
30 		asm("" : "=a" (__low), "=d" (__high) : "A" (n));\
31 		__upper = __high;				\
32 		if (__high) {					\
33 			__upper = __high % (__base);		\
34 			__high = __high / (__base);		\
35 		}						\
36 		asm("divl %2" : "=a" (__low), "=d" (__mod)	\
37 			: "rm" (__base), "0" (__low), "1" (__upper));	\
38 		asm("" : "=A" (n) : "a" (__low), "d" (__high));	\
39 	}							\
40 	__mod;							\
41 })
42 
div_u64_rem(u64 dividend,u32 divisor,u32 * remainder)43 static inline u64 div_u64_rem(u64 dividend, u32 divisor, u32 *remainder)
44 {
45 	union {
46 		u64 v64;
47 		u32 v32[2];
48 	} d = { dividend };
49 	u32 upper;
50 
51 	upper = d.v32[1];
52 	d.v32[1] = 0;
53 	if (upper >= divisor) {
54 		d.v32[1] = upper / divisor;
55 		upper %= divisor;
56 	}
57 	asm ("divl %2" : "=a" (d.v32[0]), "=d" (*remainder) :
58 		"rm" (divisor), "0" (d.v32[0]), "1" (upper));
59 	return d.v64;
60 }
61 #define div_u64_rem	div_u64_rem
62 
mul_u32_u32(u32 a,u32 b)63 static inline u64 mul_u32_u32(u32 a, u32 b)
64 {
65 	u32 high, low;
66 
67 	asm ("mull %[b]" : "=a" (low), "=d" (high)
68 			 : [a] "a" (a), [b] "rm" (b) );
69 
70 	return low | ((u64)high) << 32;
71 }
72 #define mul_u32_u32 mul_u32_u32
73 
74 /*
75  * __div64_32() is never called on x86, so prevent the
76  * generic definition from getting built.
77  */
78 #define __div64_32
79 
80 #else
81 # include <asm-generic/div64.h>
82 
83 /*
84  * Will generate an #DE when the result doesn't fit u64, could fix with an
85  * __ex_table[] entry when it becomes an issue.
86  */
mul_u64_u64_div_u64(u64 a,u64 mul,u64 div)87 static inline u64 mul_u64_u64_div_u64(u64 a, u64 mul, u64 div)
88 {
89 	u64 q;
90 
91 	asm ("mulq %2; divq %3" : "=a" (q)
92 				: "a" (a), "rm" (mul), "rm" (div)
93 				: "rdx");
94 
95 	return q;
96 }
97 #define mul_u64_u64_div_u64 mul_u64_u64_div_u64
98 
mul_u64_u32_div(u64 a,u32 mul,u32 div)99 static inline u64 mul_u64_u32_div(u64 a, u32 mul, u32 div)
100 {
101 	return mul_u64_u64_div_u64(a, mul, div);
102 }
103 #define mul_u64_u32_div	mul_u64_u32_div
104 
105 #endif /* CONFIG_X86_32 */
106 
107 #endif /* _ASM_X86_DIV64_H */
108