compat/bswap.h

   1 /*
   2  * Let's make sure we always have a sane definition for ntohl()/htonl().
   3  * Some libraries define those as a function call, just to perform byte
   4  * shifting, bringing significant overhead to what should be a simple
   5  * operation.
   6  */
   7
   8 /*
   9  * Default version that the compiler ought to optimize properly with
  10  * constant values.
  11  */
  12 static inline uint32_t default_swab32(uint32_t val)
  13 {
  14         return (((val & 0xff000000) >> 24) |
  15                 ((val & 0x00ff0000) >>  8) |
  16                 ((val & 0x0000ff00) <<  8) |
  17                 ((val & 0x000000ff) << 24));
  18 }
  19
  20 static inline uint64_t default_bswap64(uint64_t val)
  21 {
  22         return (((val & (uint64_t)0x00000000000000ffULL) << 56) |
  23                 ((val & (uint64_t)0x000000000000ff00ULL) << 40) |
  24                 ((val & (uint64_t)0x0000000000ff0000ULL) << 24) |
  25                 ((val & (uint64_t)0x00000000ff000000ULL) <<  8) |
  26                 ((val & (uint64_t)0x000000ff00000000ULL) >>  8) |
  27                 ((val & (uint64_t)0x0000ff0000000000ULL) >> 24) |
  28                 ((val & (uint64_t)0x00ff000000000000ULL) >> 40) |
  29                 ((val & (uint64_t)0xff00000000000000ULL) >> 56));
  30 }
  31
  32 #undef bswap32
  33 #undef bswap64
  34
  35 #if defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__))
  36
  37 #define bswap32 git_bswap32
  38 static inline uint32_t git_bswap32(uint32_t x)
  39 {
  40         uint32_t result;
  41         if (__builtin_constant_p(x))
  42                 result = default_swab32(x);
  43         else
  44                 __asm__("bswap %0" : "=r" (result) : "0" (x));
  45         return result;
  46 }
  47
  48 #define bswap64 git_bswap64
  49 #if defined(__x86_64__)
  50 static inline uint64_t git_bswap64(uint64_t x)
  51 {
  52         uint64_t result;
  53         if (__builtin_constant_p(x))
  54                 result = default_bswap64(x);
  55         else
  56                 __asm__("bswap %q0" : "=r" (result) : "0" (x));
  57         return result;
  58 }
  59 #else
  60 static inline uint64_t git_bswap64(uint64_t x)
  61 {
  62         union { uint64_t i64; uint32_t i32[2]; } tmp, result;
  63         if (__builtin_constant_p(x))
  64                 result.i64 = default_bswap64(x);
  65         else {
  66                 tmp.i64 = x;
  67                 result.i32[0] = git_bswap32(tmp.i32[1]);
  68                 result.i32[1] = git_bswap32(tmp.i32[0]);
  69         }
  70         return result.i64;
  71 }
  72 #endif
  73
  74 #elif defined(_MSC_VER) && (defined(_M_IX86) || defined(_M_X64))
  75
  76 #include <stdlib.h>
  77
  78 #define bswap32(x) _byteswap_ulong(x)
  79 #define bswap64(x) _byteswap_uint64(x)
  80
  81 #endif
  82
  83 #if defined(bswap32)
  84
  85 #undef ntohl
  86 #undef htonl
  87 #define ntohl(x) bswap32(x)
  88 #define htonl(x) bswap32(x)
  89
  90 #endif
  91
  92 #if defined(bswap64)
  93
  94 #undef ntohll
  95 #undef htonll
  96 #define ntohll(x) bswap64(x)
  97 #define htonll(x) bswap64(x)
  98
  99 #else
 100
 101 #undef ntohll
 102 #undef htonll
 103
 104 #if defined(__BYTE_ORDER) && defined(__LITTLE_ENDIAN) && defined(__BIG_ENDIAN)
 105
 106 # define GIT_BYTE_ORDER __BYTE_ORDER
 107 # define GIT_LITTLE_ENDIAN __LITTLE_ENDIAN
 108 # define GIT_BIG_ENDIAN __BIG_ENDIAN
 109
 110 #elif defined(BYTE_ORDER) && defined(LITTLE_ENDIAN) && defined(BIG_ENDIAN)
 111
 112 # define GIT_BYTE_ORDER BYTE_ORDER
 113 # define GIT_LITTLE_ENDIAN LITTLE_ENDIAN
 114 # define GIT_BIG_ENDIAN BIG_ENDIAN
 115
 116 #else
 117
 118 # define GIT_BIG_ENDIAN 4321
 119 # define GIT_LITTLE_ENDIAN 1234
 120
 121 # if defined(_BIG_ENDIAN) && !defined(_LITTLE_ENDIAN)
 122 #  define GIT_BYTE_ORDER GIT_BIG_ENDIAN
 123 # elif defined(_LITTLE_ENDIAN) && !defined(_BIG_ENDIAN)
 124 #  define GIT_BYTE_ORDER GIT_LITTLE_ENDIAN
 125 # else
 126 #  error "Cannot determine endianness"
 127 # endif
 128
 129 #endif
 130
 131 #if GIT_BYTE_ORDER == GIT_BIG_ENDIAN
 132 # define ntohll(n) (n)
 133 # define htonll(n) (n)
 134 #else
 135 # define ntohll(n) default_bswap64(n)
 136 # define htonll(n) default_bswap64(n)
 137 #endif
 138
 139 #endif
 140
 141 /*
 142  * Performance might be improved if the CPU architecture is OK with
 143  * unaligned 32-bit loads and a fast ntohl() is available.
 144  * Otherwise fall back to byte loads and shifts which is portable,
 145  * and is faster on architectures with memory alignment issues.
 146  */
 147
 148 #if defined(__i386__) || defined(__x86_64__) || \
 149     defined(_M_IX86) || defined(_M_X64) || \
 150     defined(__ppc__) || defined(__ppc64__) || \
 151     defined(__powerpc__) || defined(__powerpc64__) || \
 152     defined(__s390__) || defined(__s390x__)
 153
 154 #define get_be16(p)     ntohs(*(unsigned short *)(p))
 155 #define get_be32(p)     ntohl(*(unsigned int *)(p))
 156 #define put_be32(p, v)  do { *(unsigned int *)(p) = htonl(v); } while (0)
 157
 158 #else
 159
 160 #define get_be16(p)     ( \
 161         (*((unsigned char *)(p) + 0) << 8) | \
 162         (*((unsigned char *)(p) + 1) << 0) )
 163 #define get_be32(p)     ( \
 164         (*((unsigned char *)(p) + 0) << 24) | \
 165         (*((unsigned char *)(p) + 1) << 16) | \
 166         (*((unsigned char *)(p) + 2) <<  8) | \
 167         (*((unsigned char *)(p) + 3) <<  0) )
 168 #define put_be32(p, v)  do { \
 169         unsigned int __v = (v); \
 170         *((unsigned char *)(p) + 0) = __v >> 24; \
 171         *((unsigned char *)(p) + 1) = __v >> 16; \
 172         *((unsigned char *)(p) + 2) = __v >>  8; \
 173         *((unsigned char *)(p) + 3) = __v >>  0; } while (0)
 174
 175 #endif