LXR linux/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 <linux/types.h>
  20
  21#if !defined(__STRICT_ANSI__) || defined(__KERNEL__)
  22#  define __SWAB_64_THRU_32__
  23#endif
  24
  25#if defined(__KERNEL__) && __LINUX_ARM_ARCH__ >= 6
  26
  27static inline __attribute_const__ __u16 __arch_swab16(__u16 x)
  28{
  29        __asm__ ("rev16 %0, %1" : "=r" (x) : "r" (x));
  30        return x;
  31}
  32#define __arch_swab16 __arch_swab16
  33
  34static inline __attribute_const__ __u32 __arch_swab32(__u32 x)
  35{
  36        __asm__ ("rev %0, %1" : "=r" (x) : "r" (x));
  37        return x;
  38}
  39#define __arch_swab32 __arch_swab32
  40
  41#else
  42
  43static inline __attribute_const__ __u32 __arch_swab32(__u32 x)
  44{
  45        __u32 t;
  46
  47#ifndef __thumb__
  48        if (!__builtin_constant_p(x)) {
  49                /*
  50                 * The compiler needs a bit of a hint here to always do the
  51                 * right thing and not screw it up to different degrees
  52                 * depending on the gcc version.
  53                 */
  54                asm ("eor\t%0, %1, %1, ror #16" : "=r" (t) : "r" (x));
  55        } else
  56#endif
  57                t = x ^ ((x << 16) | (x >> 16)); /* eor r1,r0,r0,ror #16 */
  58
  59        x = (x << 24) | (x >> 8);               /* mov r0,r0,ror #8      */
  60        t &= ~0x00FF0000;                       /* bic r1,r1,#0x00FF0000 */
  61        x ^= (t >> 8);                          /* eor r0,r0,r1,lsr #8   */
  62
  63        return x;
  64}
  65#define __arch_swab32 __arch_swab32
  66
  67#endif
  68
  69#endif
  70