Sudoku verifier using bit fields

char VerifySudoku(char grid[81])
{
unsigned int bitFlags = 0;
unsigned short buffer; // to speed up things
char r, c;

for (r = 0; r < bitflags =" 0,">
{
for (c = 0; c <>
{
buffer = r/3*3+c/3;

// check horizontally
bitFlags |= 1 << (27-grid[(r<<3)+r+c])>
// check vertically
| 1 << (18-grid[(c<<3)+c+r])
// check subgrids
| 1 << (9-grid[(buffer<<3)+buffer+r%3*3+c%3]);
}
if (bitFlags != 0x7ffffff)
return 0;
}
return 1;
}