newlib/libc/string/swab.c

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