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<p class="MsoNormal"><b><span style="font-size:12.0pt;color:black">From: </span></b><span style="font-size:12.0pt;color:black">Prentice Bisbal <pbisbal@pppl.gov><br>
<b>Date: </b>Tuesday, October 20, 2020 at 9:40 AM<br>
<b>To: </b>John Hearns <hearnsj@gmail.com>, Jim Lux <james.p.lux@jpl.nasa.gov><br>
<b>Cc: </b>"Renfro, Michael" <Renfro@tntech.edu>, "beowulf@beowulf.org" <beowulf@beowulf.org><br>
<b>Subject: </b>Re: [Beowulf] ***UNCHECKED*** Re: Re: [EXTERNAL] Re: Re: Spark, Julia, OpenMPI etc. - all in one place<o:p></o:p></span></p>
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<p class="MsoNormal">Indexing from zero - who ever heard of zero of a thing. Damn quiche eaters.<o:p></o:p></p>
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<p>I've heard it explained this way: Index zero requires zero offset from the start of the array's memory address, so the index presents how many offsets the item is away from the start of the array.<o:p></o:p></p>
<p>Makes more sense when you think of it that way. But again, it makes more sense in lower languages like C than it does in "higher" languages like Fortran and Python where memory addressing details aren't exposed to the programmer.
<o:p></o:p></p>
<p>Prentice<o:p></o:p></p>
<p>Exactly – it’s a nice thing in C, because C isn’t really implementing arrays per se, the Array variable is a pointer, and the a[i] notation is basically a shorthand for pointer arithmetic. And it’s close to the target executable. I think, when C was first
developed, folks weren’t worrying about optimizers, for instance. <br>
<br>
You can do horrible things like <o:p></o:p></p>
<p>int a[100];<o:p></o:p></p>
<p>/* some code */<o:p></o:p></p>
<p>a[i] = *(a+j); /* someone using both array style and pointer style references, just because they can */<o:p></o:p></p>
<p>and<o:p></o:p></p>
<p>a = &somehexconstant;<o:p></o:p></p>
<p>Handy for mapping to a buffer of characters at some address, but full of traps for the unwary<o:p></o:p></p>
<p><o:p> </o:p></p>
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