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
43static 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
63/*
64 * gcc tends to zero extend 32bit values and do full 64bit maths.
65 * Define asm functions that avoid this.
66 * (clang generates better code for the C versions.)
67 */
68#ifndef __clang__
69static inline u64 mul_u32_u32(u32 a, u32 b)
70{
71 u32 high, low;
72
73 asm ("mull %[b]" : "=a" (low), "=d" (high)
74 : [a] "a" (a), [b] "rm" (b) );
75
76 return low | ((u64)high) << 32;
77}
78#define mul_u32_u32 mul_u32_u32
79
80static inline u64 add_u64_u32(u64 a, u32 b)
81{
82 u32 high = a >> 32, low = a;
83
84 asm ("addl %[b], %[low]; adcl $0, %[high]"
85 : [low] "+r" (low), [high] "+r" (high)
86 : [b] "rm" (b) );
87
88 return low | (u64)high << 32;
89}
90#define add_u64_u32 add_u64_u32
91#endif
92
93/*
94 * __div64_32() is never called on x86, so prevent the
95 * generic definition from getting built.
96 */
97#define __div64_32
98
99#else
100# include <asm-generic/div64.h>
101
102/*
103 * Will generate an #DE when the result doesn't fit u64, could fix with an
104 * __ex_table[] entry when it becomes an issue.
105 */
106static inline u64 mul_u64_add_u64_div_u64(u64 rax, u64 mul, u64 add, u64 div)
107{
108 u64 rdx;
109
110 asm ("mulq %[mul]" : "+a" (rax), "=d" (rdx) : [mul] "rm" (mul));
111
112 if (!statically_true(!add))
113 asm ("addq %[add], %[lo]; adcq $0, %[hi]" :
114 [lo] "+r" (rax), [hi] "+r" (rdx) : [add] "irm" (add));
115
116 asm ("divq %[div]" : "+a" (rax), "+d" (rdx) : [div] "rm" (div));
117
118 return rax;
119}
120#define mul_u64_add_u64_div_u64 mul_u64_add_u64_div_u64
121
122static inline u64 mul_u64_u32_div(u64 a, u32 mul, u32 div)
123{
124 return mul_u64_add_u64_div_u64(rax: a, mul, add: 0, div);
125}
126#define mul_u64_u32_div mul_u64_u32_div
127
128#endif /* CONFIG_X86_32 */
129
130#endif /* _ASM_X86_DIV64_H */
131

source code of linux/arch/x86/include/asm/div64.h