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