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Equivalent code?

Walt Conley

Hello Everyone:

In the following example seq_address is an unsigned long and obj->cmd_reg[] is an unsigned char array.

seq_address = (ulong)obj->cmd_reg[3] << 24
            + (ulong)obj->cmd_reg[2] << 16
            + (ulong)obj->cmd_reg[1] <<  8
            + (ulong)obj->cmd_reg[0];

seq_address = (ulong)obj->cmd_reg[3] * 16777216
            + (ulong)obj->cmd_reg[2] * 65536
            + (ulong)obj->cmd_reg[1] * 256
            + (ulong)obj->cmd_reg[0];
I want to combine the four bytes of data from the array and store it as an unsigned long in seq_address. I first tried the code in the first example but it does not work (seq_address is always 0). The code in the second example works. Does anyone see a reason both examples should not do the exact same thing.

-Walt

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    Extra parentheses seem to have fixed it:

    seq_address = ((ulong)obj->cmd_reg[3] << 24)
            + ((ulong)obj->cmd_reg[2] << 16)
            + ((ulong)obj->cmd_reg[1] <<  8)
            + (ulong)obj->cmd_reg[0];
    I could never memorize all those priorities. I try to use parentheses whenever I'm in doubt :-))

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  • 0

    Extra parentheses seem to have fixed it:

    seq_address = ((ulong)obj->cmd_reg[3] << 24)
            + ((ulong)obj->cmd_reg[2] << 16)
            + ((ulong)obj->cmd_reg[1] <<  8)
            + (ulong)obj->cmd_reg[0];
    I could never memorize all those priorities. I try to use parentheses whenever I'm in doubt :-))

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