memtrans.c

来自「Many C samples. It is a good sample for 」· C语言 代码 · 共 46 行

/*  File   : memtrans.c
    Author : Richard A. O'Keefe.
    Updated: 2 June 1984
    Defines: memtrans()

    memtrans(dst, src, from, to, len)
    copies exactly len characters from src[] to dst[], translating chars
    in from[] to corresponding characters in to[].   From[] and to[] are
    handled by _str2map. BEWARE: _str2map normally expects characters in
    the range 0..127.  The Vax MOVTC instruction thinks its table is 256
    bytes long; if you want to translate arbitrary bytes you'd better be
    sure that the _map_vec array is 256 bytes long.  As distributed, the
    memtrans function is only for translating ASCII (to 8-bit codes).

    The VaxAsm code can only handle 0 <= len < 2^16, and is presented as
    usual for your interest and amusement.  Why *do* designers of 32-bit
    machines put 16-bit limits on strings?  (Dec aren't the only ones.)
*/

#include "strings.h"
#include "_str2map.h"

#if	VaxAsm

void memtrans(dst, src, from, to, len)
    _char_ *dst, *src, *from, *to;
    int len;
    {
	_str2map(0, from, to);
	asm("movtc 20(ap),*8(ap),$0,__map_vec,20(ap),*4(ap)");
    }

#else  ~VaxAsm

void memtrans(dst, src, from, to, len)
    register _char_ *dst, *src;
    _char_ *from, *to;
    register int len;
    {
	_str2map(0, from, to);
	while (--len >= 0) *dst++ = _map_vec[*src++];
    }

#endif	VaxAsm