Category : C Source Code
Archive   : TIFTOOL.ZIP
Filename : SWAP.C

/* swap.c - routines to swap (reverse) words and double words
*/
#include "aldtypes.h"
#include "swap.h"

/* swap bytes within words -- overlapping arrays are handled properly
*/
void swab (lpSrc, lpDst, nbytes)
register LPSTR lpSrc, lpDst; /* assumed to be word-aligned */
WORD nbytes; /* assumed to be even */
{
register WORD words;
union {
char c[2];
WORD w;
} wrd;

words = nbytes/2;

if (lpDst <= lpSrc || lpDst >= lpSrc + nbytes) {
for (; words--; lpSrc += 2) {
wrd.w = *(WORD FAR *)lpSrc;
*lpDst++ = *(LPSTR)(wrd.c + 1); /* W2 doesn't like wrd.c[1] */
*lpDst++ = *(LPSTR)(wrd.c);
}
}
else { /* we'll have to go backward */
lpSrc += nbytes - sizeof(WORD);
lpDst += nbytes - 1;
for (; words--; lpSrc -= 2) {
wrd.w = *(WORD FAR *)lpSrc;
*lpDst-- = *(LPSTR)(wrd.c);
*lpDst-- = *(LPSTR)(wrd.c + 1);
}
}
}

/* swap words -- overlapping ranges are handled properly
*
* actually, does a 4-byte reversal
*/
void swaw (lpSrc, lpDst, nbytes)
register LPSTR lpSrc, lpDst; /* assumed to be word-aligned */
WORD nbytes; /* assumed to be multiple of 4 */
{
register WORD dwords;
union {
char c[4];
DWORD dw;
} dwrd;

dwords = nbytes/4;

if (lpDst <= lpSrc || lpDst >= lpSrc + nbytes) {
for (; dwords--; lpSrc += 4) {
dwrd.dw = *(DWORD FAR *)lpSrc;
*lpDst++ = *(LPSTR)(dwrd.c + 3);
*lpDst++ = *(LPSTR)(dwrd.c + 2);
*lpDst++ = *(LPSTR)(dwrd.c + 1);
*lpDst++ = *(LPSTR)(dwrd.c);
}
}
else { /* we'll have to go backward */
lpSrc += nbytes - sizeof(DWORD);
lpDst += nbytes - 1;
for (; dwords--; lpSrc -= 4) {
dwrd.dw = *(DWORD FAR *)lpSrc;
*lpDst-- = *(LPSTR)(dwrd.c);
*lpDst-- = *(LPSTR)(dwrd.c + 1);
*lpDst-- = *(LPSTR)(dwrd.c + 2);
*lpDst-- = *(LPSTR)(dwrd.c + 3);
}
}
}