CODEWITHSUNDEEP
assemblybinaryhexasciibit-manipulation
Zzz
Zzz

Reputation: 3025

Converting numbers to ASCII in assembly

Can someone explain why doing an OR operation on a binary number with 0x0030 as the operand produces the ASCII character of that number?

Upvotes: 1

Views: 30678

Answers (3)

Chimera
Chimera

Reputation: 6018

Because looking at the ASCII chart, the digits 0 through nine start at 0x30. So you want the ASCII value for character 1? 0x30 or 0x01 = 0x31 = ASCII value for the number 1.

In binary it's easy to see:

(0x30)   110000
or
(0x01)   000001
=        110001

Which is 0x31 - ASCII value of 1.

enter image description here

Upvotes: 6

Andreas Fester
Andreas Fester

Reputation: 36630

Look at the binary representation of a single digit: e.g. 2d = 00000010b. Apply an OR-operation with 0x30 (00110000b) to it. This results in 00110010b which is 0x32 or 50d which is the ASCII-code for '2'. Effectively, in this case (since there are no carries to consider) the OR-operation is equal to adding 0x30.

Upvotes: 1

sinelaw
sinelaw

Reputation: 16553

If you're referring to numbers 0 through 9, the reason is that 0x30 (or 48) is the ASCII code of the number 0. Since 48 requires only bits in the higher (left hand) side of a byte, ORing it with any number below 16 (lower bits) is the same as mathematically adding the numbers.

So 0x30 OR 0x01 will give 0x31, the ASCII code of the character '1', and so on.

Upvotes: 2

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