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/*----------------------------------------------------------------------------
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;
}
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