Explanation on preprocessor directive

[seforo]

Can someone explain for me what this guy is doing here. N.B homer_uint64 is a defined data type

#define CLUSTERS_DATAID ((homer_uint64) 'CLUS' << 32 | (homer_uint64)' TERS')

[Savage]

[QUOTE]

Can someone explain for me what this guy is doing here. N.B homer_uint64 is a defined data type

#define CLUSTERS_DATAID ((homer_uint64) 'CLUS' << 32 | (homer_uint64)' TERS')

This macro would only produce compiler errors when used.
Are you sure that he didn't use quotes to wrap CLUS and TERS instead of apostrophes?

In the rest of this post I will assume he had used quotes.So lets break down this macro.

First part of macro:

(homer_uint64)" CLUS"<<32 does the following:
1.It converts a const string "CLUS" to homer_uint64
2.It shifts its bits for 32 places to the left.

C=0x43
L=0x4C
U=0x55
S=0x53

Before shifting:
0x000000434C555 3.

After shifting:
0x434C555300000 000


Second part of macro ( (homer_uint64)" TERS") also converts const string to homer_uint64 but it doesn't shift it for 32 places.

So second part is:

T=0x54
E=0x45
R=0x52
S=0x53

0x0000000054455 253

And finally bitwise operator OR(|) merges these two and creates:

0x434C555300000 000 |
0x0000000054455 253
//----------------------------------
0x434C553544552 53

[\CODE]

which the author of this macro uses as symbolic constant for cluster data.

[seforo]

He used apostrophes, I just did copy and paste. Thanks for the explanation, it highlighted me a lot.