arch/x86/include/asm/div64.h

   1 #ifndef _ASM_X86_DIV64_H
   2 #define _ASM_X86_DIV64_H
   3
   4 #ifdef CONFIG_X86_32
   5
   6 #include <linux/types.h>
   7 #include <linux/log2.h>
   8
   9 /*
  10  * do_div() is NOT a C function. It wants to return
  11  * two values (the quotient and the remainder), but
  12  * since that doesn't work very well in C, what it
  13  * does is:
  14  *
  15  * - modifies the 64-bit dividend _in_place_
  16  * - returns the 32-bit remainder
  17  *
  18  * This ends up being the most efficient "calling
  19  * convention" on x86.
  20  */
  21 #define do_div(n, base)                                         \
  22 ({                                                              \
  23         unsigned long __upper, __low, __high, __mod, __base;    \
  24         __base = (base);                                        \
  25         if (__builtin_constant_p(__base) && is_power_of_2(__base)) { \
  26                 __mod = n & (__base - 1);                       \
  27                 n >>= ilog2(__base);                            \
  28         } else {                                                \
  29                 asm("" : "=a" (__low), "=d" (__high) : "A" (n));\
  30                 __upper = __high;                               \
  31                 if (__high) {                                   \
  32                         __upper = __high % (__base);            \
  33                         __high = __high / (__base);             \
  34                 }                                               \
  35                 asm("divl %2" : "=a" (__low), "=d" (__mod)      \
  36                         : "rm" (__base), "0" (__low), "1" (__upper));   \
  37                 asm("" : "=A" (n) : "a" (__low), "d" (__high)); \
  38         }                                                       \
  39         __mod;                                                  \
  40 })
  41
  42 static inline u64 div_u64_rem(u64 dividend, u32 divisor, u32 *remainder)
  43 {
  44         union {
  45                 u64 v64;
  46                 u32 v32[2];
  47         } d = { dividend };
  48         u32 upper;
  49
  50         upper = d.v32[1];
  51         d.v32[1] = 0;
  52         if (upper >= divisor) {
  53                 d.v32[1] = upper / divisor;
  54                 upper %= divisor;
  55         }
  56         asm ("divl %2" : "=a" (d.v32[0]), "=d" (*remainder) :
  57                 "rm" (divisor), "0" (d.v32[0]), "1" (upper));
  58         return d.v64;
  59 }
  60 #define div_u64_rem     div_u64_rem
  61
  62 #else
  63 # include <asm-generic/div64.h>
  64 #endif /* CONFIG_X86_32 */
  65
  66 #endif /* _ASM_X86_DIV64_H */