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Diffstat (limited to 'buildtools/endiangen.c')
-rw-r--r-- | buildtools/endiangen.c | 97 |
1 files changed, 97 insertions, 0 deletions
diff --git a/buildtools/endiangen.c b/buildtools/endiangen.c new file mode 100644 index 00000000..07560c10 --- /dev/null +++ b/buildtools/endiangen.c @@ -0,0 +1,97 @@ +/*---------------------------------------------------------------------------- + endiangen +------------------------------------------------------------------------------ + This is a program to create C code that declares the endianness of the + machine on which it is run. + + It generates something like this: + + #ifndef LITTLE_ENDIAN + #define LITTLE_ENDIAN 1234 + #endif + + #ifndef BIG_ENDIAN + #define BIG_ENDIAN 4321 + #endif + + #ifndef BYTE_ORDER + #define BYTE_ORDER LITTLE_ENDIAN + #endif + + #define BITS_PER_WORD 32 + #endif + + + Really good code usually is not sensitive to endianness. But fast, + not-so-good code often is. The best way for code to determine + endianness is for it to do a runtime cast of an integer to an array + of characters and see where the bytes land. But if speed requires + even sleazier code than that, use these macros. + +-----------------------------------------------------------------------------*/ +#include <stdio.h> +#include <unistd.h> + +#define MAX(a,b) ((a) > (b) ? (a) : (b)) + +enum endianness {ENDIAN_LITTLE, ENDIAN_BIG}; + +static enum endianness +byteOrder(void) { + + enum endianness retval; + + union { + unsigned char arrayval[2]; + unsigned short numval; + } testunion; + + testunion.numval = 3; + + if (testunion.arrayval[0] == 3) + retval = ENDIAN_LITTLE; + else + retval = ENDIAN_BIG; + + return retval; +} + + + +static unsigned int +bitsPerWord(void) { + + return MAX(sizeof(long), sizeof(int)) * 8; +} + + + +int +main(int argc, char **argv) { + + printf("/* This was generated by the program 'endiangen' */\n"); + printf("\n"); + printf("/* LITTLE_ENDIAN, BIG_ENDIAN, and BYTE_ORDER " + "may come from the C library\n"); + printf("via ctype.h. */\n"); + printf("#include <ctype.h>\n"); + printf("#ifndef LITTLE_ENDIAN\n"); + printf("#define LITTLE_ENDIAN 1234\n"); + printf("#endif\n"); + printf("#ifndef BIG_ENDIAN\n"); + printf("#define BIG_ENDIAN 4321\n"); + printf("#endif\n"); + printf("\n"); + printf("#ifndef BYTE_ORDER\n"); + printf("#define BYTE_ORDER %s\n", + byteOrder() == ENDIAN_LITTLE ? "LITTLE_ENDIAN" : "BIG_ENDIAN"); + printf("#endif\n"); + printf("\n"); + printf("#define BITS_PER_WORD %u\n", bitsPerWord()); + + return 0; +} + + + + |