Convert from lowercase to uppercase

Question

I am trying to convert from lowercase to uppercase. I know it's easy to do

SUB AL, 20H

But I was given another solution, which is

AND AL, 0DFH

Please help me figure this out. Thanks

+3

Foo May 01 '12 at 6:50

2 answers

SUB AL, 20H subtracts 0x20 from AL

AND AL,0DFH 5 ( "0" ). 0x20 00100000, , , 5.

+2

Gil.I 01 '12 7:02

Anders lindahl · Accepted Answer · 2012-05-01T07:02:17+0000

Look at the bit patterns:

A (0x41): 0100 0001
a (0x61): 0110 0001
M (0x4d): 0100 1101
m (0x6d): 0110 1101
Z (0x5a): 0101 1010
z (0x7a): 0111 1010

The lowercase ASCII is the uppercase ASCII + 0x20 ( 0010 0000) - that is, the same bit pattern with the sixth bit set.

0xdf 1101 1111in binary format. And: using AL, which sets the sixth bit to zero, but saves other bit values.