arch/arm/include/asm/swab.h

   1 /*
   2  *  arch/arm/include/asm/byteorder.h
   3  *
   4  * ARM Endian-ness.  In little endian mode, the data bus is connected such
   5  * that byte accesses appear as:
   6  *  0 = d0...d7, 1 = d8...d15, 2 = d16...d23, 3 = d24...d31
   7  * and word accesses (data or instruction) appear as:
   8  *  d0...d31
   9  *
  10  * When in big endian mode, byte accesses appear as:
  11  *  0 = d24...d31, 1 = d16...d23, 2 = d8...d15, 3 = d0...d7
  12  * and word accesses (data or instruction) appear as:
  13  *  d0...d31
  14  */
  15 #ifndef __ASM_ARM_SWAB_H
  16 #define __ASM_ARM_SWAB_H
  17
  18 #include <linux/compiler.h>
  19 #include <asm/types.h>
  20
  21 #if !defined(__STRICT_ANSI__) || defined(__KERNEL__)
  22 #  define __SWAB_64_THRU_32__
  23 #endif
  24
  25 static inline __attribute_const__ __u32 __arch_swab32(__u32 x)
  26 {
  27         __u32 t;
  28
  29 #ifndef __thumb__
  30         if (!__builtin_constant_p(x)) {
  31                 /*
  32                  * The compiler needs a bit of a hint here to always do the
  33                  * right thing and not screw it up to different degrees
  34                  * depending on the gcc version.
  35                  */
  36                 asm ("eor\t%0, %1, %1, ror #16" : "=r" (t) : "r" (x));
  37         } else
  38 #endif
  39                 t = x ^ ((x << 16) | (x >> 16)); /* eor r1,r0,r0,ror #16 */
  40
  41         x = (x << 24) | (x >> 8);               /* mov r0,r0,ror #8      */
  42         t &= ~0x00FF0000;                       /* bic r1,r1,#0x00FF0000 */
  43         x ^= (t >> 8);                          /* eor r0,r0,r1,lsr #8   */
  44
  45         return x;
  46 }
  47 #define __arch_swab32 __arch_swab32
  48
  49 #endif
  50