arch/x86/include/asm/div64.h

   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
  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
  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 #else
  75 # include <asm-generic/div64.h>
  76 #endif /* CONFIG_X86_32 */
  77
  78 #endif /* _ASM_X86_DIV64_H */