toolchain/gcc/newlib/libc/string/swab.c

   1 /*
   2 FUNCTION
   3         <<swab>>---swap adjacent bytes
   4
   5 ANSI_SYNOPSIS
   6         #include <unistd.h>
   7         void swab(const void *<[in]>, void *<[out]>, ssize_t <[n]>);
   8
   9 TRAD_SYNOPSIS
  10         void swab(<[in]>, <[out]>, <[n]>
  11         void *<[in]>;
  12         void *<[out]>;
  13         ssize_t <[n]>;
  14
  15 DESCRIPTION
  16         This function copies <[n]> bytes from the memory region
  17         pointed to by <[in]> to the memory region pointed to by
  18         <[out]>, exchanging adjacent even and odd bytes.
  19
  20 PORTABILITY
  21 <<swab>> requires no supporting OS subroutines.
  22 */
  23
  24 #include <unistd.h>
  25
  26 void
  27 _DEFUN (swab, (b1, b2, length),
  28         _CONST void *b1 _AND
  29         void *b2 _AND
  30         ssize_t length)
  31 {
  32   const char *from = b1;
  33   char *to = b2;
  34   ssize_t ptr;
  35   for (ptr = 1; ptr < length; ptr += 2)
  36     {
  37       char p = from[ptr];
  38       char q = from[ptr-1];
  39       to[ptr-1] = p;
  40       to[ptr  ] = q;
  41     }
  42   if (ptr == length) /* I.e., if length is odd, */
  43     to[ptr-1] = 0;   /* then pad with a NUL. */
  44 }