On Mon, 12 Jan 2004 20:01:17 +0100 (MET) [EMAIL PROTECTED] wrote: | From: Alan Stern <[EMAIL PROTECTED]> | | > > - ptr[4] = MSB_of(info->pagesize>>16); | > > - ptr[5] = LSB_of(info->pagesize>>16); | > > - ptr[6] = MSB_of(info->pagesize&0xFFFF); | > > - ptr[7] = LSB_of(info->pagesize&0xFFFF); | > > + ((u32 *) ptr)[1] = cpu_to_be32(info->pagesize); | > > | > > A good compiler generates the same code, and for a human | > > like me the above four statements show much more clearly | > > that values are assigned to ptr[4..7] than the ugly cast below. | | My opinion is slightly mixed. I definitely think the old way is too | repetitive, unclear, and error-prone. On the other hand, I also dislike | the ugly cast. A possible alternative, also ugly ...
First, let's agree that it's ugly and not needed. There are better (more readable and understandable) ways to do it, so choose and use one. | Let me tell you - I have programmed for twenty years without | knowing the meaning of little-endian and big-endian. Yes, | they had something to do with the order of bytes in an integer, | but there are many strange architectures and mixed versions, | and there is no need at all to know such things. | Yes, knowing such things is directly harmful. I can only see this if you don't do hardware interface programming or if you do but it's all on one $ARCH. There are places (like USB host controller drivers) that using endian swapping is necessary. | Seeing such a cast must raise an alarm. Caution! Bug ahead! | And indeed, I glanced over these patches and saw two casts, | one of them buggy. 50%. | | If one has a char * then only use it to read or write chars. | If one has an int * then only use it to read or write ints. | Never use a cast. | | There are even architectures where the size of a char * differs | from that of an int *. One never knows whether the compiler is going | to change the bit pattern upon such a cast or not. | | And then there are alignment restrictions. | If you really want to write one line of obscure code that | replaces 4 byte assignments, then the reader gets an additional | obligation, namely to check that this char * is suitably aligned | to be abused as int *. | | Altogether ugliness. Forgivable in case efficiency matters, | and it really does make a difference. Not elsewhere. -- ~Randy ------------------------------------------------------- This SF.net email is sponsored by: Perforce Software. Perforce is the Fast Software Configuration Management System offering advanced branching capabilities and atomic changes on 50+ platforms. Free Eval! http://www.perforce.com/perforce/loadprog.html _______________________________________________ [EMAIL PROTECTED] To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
