Question for "<<"

Hi

Noone know this ??

why a = 1 << b

when b = 0 , a is not always equal 1

why??

Hi

Noone know this ??

why a = 1 << b

when b = 0 , a is not always equal 1

why??

"Noone know this ??"

I don't think anyone is convinced that b=0.

Try compiling a simple test case in isolation, if it gives the correct result take another look at 'b' to see whether it is actually 1.

The section of your code that does the shifting is this bit:

0024 7401   MOV A,#01H
0026 A807   MOV R0,AR7
0028 08     INC R0
0029 8002   SJMP ?C0181
002B ?C0180:
002B C3     CLR C
002C 33     RLC A
002D ?C0181:
002D D8FC   DJNZ R0,?C0180
002F FF     MOV R7,A

Thanks for replay

I have a ready to this ,Please see it

#define ENABLE 1
uchar volatile xdata *ptr_reg=0x8000;
bug0 =0;
bug1 =0;

uchar b = pre_reg[0];

a = (ENABLE << b);

if ( b != 0 ) bug0++;
if ( a != 1 ) bug1++;

after I run this ,bug0 is zero ,but bug1
is nonzero.

I also have run this code in VC60,and it work fine.

Thanks for your kind help

Thank to Graham

I also think the asm code is fine,
but I realy got a wrong answer ><

maybe I have setting something wrong&#12290;

For now,I just use switch-case to do
this sample work.

uchar volatile xdata *ptr_reg=0x8000;
bug0 =0;
bug1 =0;

uchar b = pre_reg[0];

Thanks for correct my type error^^"""

Sorry,I have already delete the code
so i just type it again.

It is ptr_reg not pre_reg&#12290;

Thanks a lot

Do you call the function from an interrupt service routine. The code that you have posted works correct for registerbank 0, but will fail if you call it from an interrupt service routine that uses a different register bank.

See also: http://www.keil.com/support/docs/2201.htm


Reinhard