这几天要在ABAP中实现 3DES 标准对称加密算法，与其他外部系统进行加密/解密操作。由于ABAP语言中没有 左移 <<、无符号右移 >>> 操作，只能自己实现
思路：
如果移动的位数bit是字节（8位）的整数倍，则直接使用 SHIFT <i> BY p PLACES RIGHT IN BYTE MODE.这样的语句搞定（这样效率会更高），如果非字节整数倍，则需要借助于SET BIT来完成，实现时，要注意整型的字节序格式，本人开发环境是低字节序（低位在前，高位在后），与人的阅读习惯是反的（但要注意的字节里面的是还是高位在前，低位在后），左右位移规则如下（同一种颜色为移动后所在位置）：
DATA: BEGIN OF index_map OCCURS 0,
index_inner TYPE i,
index TYPE i,
END OF index_map .
index_inner TYPE i,
index TYPE i,
END OF index_map .
FORM init .
CLEAR: index_map[].
index_map-index_inner = 1.
index_map-index = 8.
APPEND index_map.
index_map-index_inner = 2.
index_map-index = 7.
APPEND index_map.
index_map-index_inner = 3.
index_map-index = 6.
APPEND index_map.
index_map-index_inner = 4.
index_map-index = 5.
APPEND index_map.
index_map-index_inner = 5.
index_map-index = 4.
APPEND index_map.
index_map-index_inner = 6.
index_map-index = 3.
APPEND index_map.
index_map-index_inner = 7.
index_map-index = 2.
APPEND index_map.
index_map-index_inner = 8.
index_map-index = 1.
APPEND index_map.
index_map-index_inner = 9.
index_map-index = 16.
APPEND index_map.
index_map-index_inner = 10.
index_map-index = 15.
APPEND index_map.
index_map-index_inner = 11.
index_map-index = 14.
APPEND index_map.
index_map-index_inner = 12.
index_map-index = 13.
APPEND index_map.
index_map-index_inner = 13.
index_map-index = 12.
APPEND index_map.
index_map-index_inner = 14.
index_map-index = 11.
APPEND index_map.
index_map-index_inner = 15.
index_map-index = 10.
APPEND index_map.
index_map-index_inner = 16.
index_map-index = 9.
APPEND index_map.
index_map-index_inner = 17.
index_map-index = 24.
APPEND index_map.
index_map-index_inner = 18.
index_map-index = 23.
APPEND index_map.
index_map-index_inner = 19.
index_map-index = 22.
APPEND index_map.
index_map-index_inner = 20.
index_map-index = 21.
APPEND index_map.
index_map-index_inner = 21.
index_map-index = 20.
APPEND index_map.
index_map-index_inner = 22.
index_map-index = 19.
APPEND index_map.
index_map-index_inner = 23.
index_map-index = 18.
APPEND index_map.
index_map-index_inner = 24.
index_map-index = 17.
APPEND index_map.
index_map-index_inner = 25.
index_map-index = 32.
APPEND index_map.
index_map-index_inner = 26.
index_map-index = 31.
APPEND index_map.
index_map-index_inner = 27.
index_map-index = 30.
APPEND index_map.
index_map-index_inner = 28.
index_map-index = 29.
APPEND index_map.
index_map-index_inner = 29.
index_map-index = 28.
APPEND index_map.
index_map-index_inner = 30.
index_map-index = 27.
APPEND index_map.
index_map-index_inner = 31.
index_map-index = 26.
APPEND index_map.
index_map-index_inner = 32.
index_map-index = 25.
APPEND index_map.
ENDFORM.
CLEAR: index_map[].
index_map-index_inner = 1.
index_map-index = 8.
APPEND index_map.
index_map-index_inner = 2.
index_map-index = 7.
APPEND index_map.
index_map-index_inner = 3.
index_map-index = 6.
APPEND index_map.
index_map-index_inner = 4.
index_map-index = 5.
APPEND index_map.
index_map-index_inner = 5.
index_map-index = 4.
APPEND index_map.
index_map-index_inner = 6.
index_map-index = 3.
APPEND index_map.
index_map-index_inner = 7.
index_map-index = 2.
APPEND index_map.
index_map-index_inner = 8.
index_map-index = 1.
APPEND index_map.
index_map-index_inner = 9.
index_map-index = 16.
APPEND index_map.
index_map-index_inner = 10.
index_map-index = 15.
APPEND index_map.
index_map-index_inner = 11.
index_map-index = 14.
APPEND index_map.
index_map-index_inner = 12.
index_map-index = 13.
APPEND index_map.
index_map-index_inner = 13.
index_map-index = 12.
APPEND index_map.
index_map-index_inner = 14.
index_map-index = 11.
APPEND index_map.
index_map-index_inner = 15.
index_map-index = 10.
APPEND index_map.
index_map-index_inner = 16.
index_map-index = 9.
APPEND index_map.
index_map-index_inner = 17.
index_map-index = 24.
APPEND index_map.
index_map-index_inner = 18.
index_map-index = 23.
APPEND index_map.
index_map-index_inner = 19.
index_map-index = 22.
APPEND index_map.
index_map-index_inner = 20.
index_map-index = 21.
APPEND index_map.
index_map-index_inner = 21.
index_map-index = 20.
APPEND index_map.
index_map-index_inner = 22.
index_map-index = 19.
APPEND index_map.
index_map-index_inner = 23.
index_map-index = 18.
APPEND index_map.
index_map-index_inner = 24.
index_map-index = 17.
APPEND index_map.
index_map-index_inner = 25.
index_map-index = 32.
APPEND index_map.
index_map-index_inner = 26.
index_map-index = 31.
APPEND index_map.
index_map-index_inner = 27.
index_map-index = 30.
APPEND index_map.
index_map-index_inner = 28.
index_map-index = 29.
APPEND index_map.
index_map-index_inner = 29.
index_map-index = 28.
APPEND index_map.
index_map-index_inner = 30.
index_map-index = 27.
APPEND index_map.
index_map-index_inner = 31.
index_map-index = 26.
APPEND index_map.
index_map-index_inner = 32.
index_map-index = 25.
APPEND index_map.
ENDFORM.
*&---------------------------------------------------------------------*
*& Form lshfit_i
*&---------------------------------------------------------------------*
* 整型左移
*----------------------------------------------------------------------*
* -->I 待位移的数
* -->PLACES 移几位
* -->I2 位移后的数
*----------------------------------------------------------------------*
FORM lshfit_i USING i TYPE i places TYPE i i2 TYPE i.
DATA: start1 TYPE i ,start2 TYPE i.
DATA: b TYPE n.
DATA: i3 TYPE i.
FIELD-SYMBOLS: <i3> TYPE x.
FIELD-SYMBOLS: <i> TYPE x.
FIELD-SYMBOLS: <p> TYPE x.
DATA: _31(4) TYPE x,p TYPE i.
p = places.
IF places < 0.
_31 = '1F000000'.
ASSIGN p TO <p> CASTING.
<p> = <p> BIT-AND _31.
ENDIF.
i2 = i.
ASSIGN i2 TO <i> CASTING.
IF p = 24 OR p = 16 OR p = 8.
p = p / 8.
SHIFT <i> BY p PLACES RIGHT IN BYTE MODE.
ELSE.
ASSIGN i3 TO <i3> CASTING.
start1 = 32 - p.
WHILE start1 >= 1.
READ TABLE index_map INDEX start1.
GET BIT index_map-index OF <i> INTO b.
IF b = 1.
start2 = start1 + p.
READ TABLE index_map INDEX start2.
SET BIT index_map-index OF <i3> TO b.
ENDIF.
start1 = start1 - 1.
ENDWHILE.
<i> = <i3>.
ENDIF.
ENDFORM. "lshfit_i
*&---------------------------------------------------------------------*
*& Form rshfit_i
*&---------------------------------------------------------------------*
* 整型右移
*----------------------------------------------------------------------*
* -->I 待位移的数
* -->PLACES 移几位
* -->I2 位移后的数
*----------------------------------------------------------------------*
FORM rshfit_i USING i TYPE i places TYPE i i2 TYPE i.
DATA: start1 TYPE i ,start2 TYPE i.
DATA: b TYPE n.
DATA: i3 TYPE i.
FIELD-SYMBOLS: <i3> TYPE x.
FIELD-SYMBOLS: <i> TYPE x.
FIELD-SYMBOLS: <p> TYPE x.
DATA: _31(4) TYPE x,p TYPE i.
DATA multiplier TYPE i.
p = places.
IF p < 0.
_31 = '1F000000'.
ASSIGN p TO <p> CASTING.
<p> = <p> BIT-AND _31.
ENDIF.
i2 = i.
ASSIGN i2 TO <i> CASTING.
IF p = 24 OR p = 16 OR p = 8.
p = p / 8.
SHIFT <i> BY p PLACES LEFT IN BYTE MODE.
ELSE.
IF i >= 0 AND p < 31 .
multiplier = 2 ** p.
i2 = i DIV multiplier.
ELSE.
ASSIGN i3 TO <i3> CASTING.
start1 = p + 1.
WHILE start1 <= 32.
READ TABLE index_map INDEX start1.
GET BIT index_map-index OF <i> INTO b.
IF b = 1.
start2 = start1 - p.
READ TABLE index_map INDEX start2.
SET BIT index_map-index OF <i3> TO b.
ENDIF.
start1 = start1 + 1.
ENDWHILE.
<i> = <i3>.
ENDIF.
ENDIF.
ENDFORM. "rshfit_i
*&---------------------------------------------------------------------*
*& Form c2int
*&---------------------------------------------------------------------*
* 字符转整型
*----------------------------------------------------------------------*
* -->C1 text
* -->I text
*----------------------------------------------------------------------*
FORM c2int USING c1 TYPE c i TYPE i.
FIELD-SYMBOLS <c1> TYPE x.
FIELD-SYMBOLS: <i> TYPE x.
ASSIGN c1 TO <c1> CASTING.
ASSIGN i TO <i> CASTING.
<i> = <c1>.
ENDFORM.
*& Form c2int
*&---------------------------------------------------------------------*
* 字符转整型
*----------------------------------------------------------------------*
* -->C1 text
* -->I text
*----------------------------------------------------------------------*
FORM c2int USING c1 TYPE c i TYPE i.
FIELD-SYMBOLS <c1> TYPE x.
FIELD-SYMBOLS: <i> TYPE x.
ASSIGN c1 TO <c1> CASTING.
ASSIGN i TO <i> CASTING.
<i> = <c1>.
ENDFORM.
*&---------------------------------------------------------------------*
*& Form lshfit_c
*&---------------------------------------------------------------------*
* 字符左移
*----------------------------------------------------------------------*
* -->C1 待位移的字符
* -->PLACES 移几位
* -->I 位移后的结果
*----------------------------------------------------------------------*
FORM lshfit_c USING c1 TYPE c places TYPE i i TYPE i.
PERFORM c2int USING c1 i.
PERFORM lshfit_i USING i places i.
ENDFORM. "lshfit
*&---------------------------------------------------------------------*
*& Form rshfit_c
*&---------------------------------------------------------------------*
* 字符右移
*----------------------------------------------------------------------*
* -->C1 待位移的字符
* -->PLACES 移几位
* -->I 位移后的结果
*----------------------------------------------------------------------*
FORM rshfit_c USING c1 TYPE c places TYPE i i TYPE i.
PERFORM c2int USING c1 i.
PERFORM rshfit_i USING i places i.
ENDFORM. "rshfit_c
*& Form lshfit_c
*&---------------------------------------------------------------------*
* 字符左移
*----------------------------------------------------------------------*
* -->C1 待位移的字符
* -->PLACES 移几位
* -->I 位移后的结果
*----------------------------------------------------------------------*
FORM lshfit_c USING c1 TYPE c places TYPE i i TYPE i.
PERFORM c2int USING c1 i.
PERFORM lshfit_i USING i places i.
ENDFORM. "lshfit
*&---------------------------------------------------------------------*
*& Form rshfit_c
*&---------------------------------------------------------------------*
* 字符右移
*----------------------------------------------------------------------*
* -->C1 待位移的字符
* -->PLACES 移几位
* -->I 位移后的结果
*----------------------------------------------------------------------*
FORM rshfit_c USING c1 TYPE c places TYPE i i TYPE i.
PERFORM c2int USING c1 i.
PERFORM rshfit_i USING i places i.
ENDFORM. "rshfit_c