>>> operator with c langage

[diep]

Hi,

i'm trying to code the bishopAttack and rookAttack.
to compute index with rotated bitboard i use this with java

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int idx_down = (int) (pieces_45 >>> DIA_DOWN_SHIFT[sq]) & 63;
int idx_up = (int) (pieces_315 >>> DIA_UP_SHIFT[sq]) & 63;

but in c, it is different.
i think i must divide by 2 my integer the number return by DIA_DOWN_SHIFT[sq].

Thanks for any help.
Best regards
Yves

While all scalar data types (char, short, int, long) in Java are signed, C distinguish signed and unsigned data types. In order to shift right with zeros from left, like Java >>>, you need to declare (or cast) the data to shift unsigned and use the same operator >> as for signed shifts, where the most significant bit (sign bit) is shifted from left.
Typically one uses a typedefinition:

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typedef unsigned long long  BitBoard;

or

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typedef unsigned long long  U64;

Heh Gerd, is Ansi-C nowadays garantueeing that in 64 bits integers right shifting of more than 32 bits is garantueed 100% ok, instead of undefined?

It's not interesting what compilers practical do, but what the language defines as being defined.

Vincent

[Gerd Isenberg]

Heh Gerd, is Ansi-C nowadays garantueeing that in 64 bits integers right shifting of more than 32 bits is garantueed 100% ok, instead of undefined?

It's not interesting what compilers practical do, but what the language defines as being defined.

Vincent

No idea exactly, but I guess shifts between 32 and 63 are guaranteed to be correct, even with ancient VC6 compiler. Where things are undefined are shifts > 63. X86-64 compiler usually emit shr instruction with implicit modulo 64, thus shift right 64 is a nop. In 32 bit mode a 64-bit shift right might result in null with certain compilers.

Gerd