source: buchla-68k/libsm/strrevi.c@ c3aee8a

/*
   =============================================================================
        strrevi.c -- reverse a string in place
        Version 1 -- 1988-02-03 -- D.N. Lynx Crowe

        char *
        strrevi(s)
        char *s;

                Reverses string 's1' in place.  Returns 's1'.
   =============================================================================
*/

int8_t *strrevi(int8_t *s)
{
        register int8_t *p1, *p2;
        register int32_t i;
        register int8_t c;

        p1 = s;                 /* initialize left end pointer */
        p2 = s;                 /* initialize right end pointer */
        i = 0L;                 /* initialize character count */

        while (*p2) {           /* find the right end of the string */

                ++i;
                ++p2;
        }

        --p2;                   /* adjust right end pointer */
        i >>= 1;                /* calculate swap count */

        while (i--) {           /* for each pair of characters ... */

                c = *p2;        /* ... swap right and left characters */
                *p2-- = *p1;
                *p1++ = c;
        }

        return(s);              /* return pointer to reversed string */
}