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Re: Generating pseudo-random integers


From: Jim Meyering
Subject: Re: Generating pseudo-random integers
Date: Sat, 14 May 2011 08:49:45 +0200

Pádraig Brady wrote:

> I've attached an updated version where I
> abstracted a sparse_map ADT so we may more
> easily change in future if required.
> I've also added a test and a NEWS entry.
...
> Subject: [PATCH] shuf: use memory more efficiently when returning a subset
>
> * gl/lib/randperm.c (randperm_new): When the number of items
> to return H, is much smaller than the total number of items N,
> use a hash to represent the sparse permutations of the set N.
> This is currently enabled for N > 128K and N/H > 32.
> * tests/misc/shuf: Ensure shuf can quickly return 2 numbers
> from a large range.
> * gl/modules/randperm: Depend on hash.
> * NEWS: Mention the change.

Thanks for doing that.
It looks perfect, though "Improvement" is more descriptive
than mere "Change" ;-)

It sounds a little better to avoid "will" in the NEWS entry.

diff --git a/NEWS b/NEWS
index 8b4c707..7a7f761 100644
--- a/NEWS
+++ b/NEWS
@@ -12,10 +12,10 @@ GNU coreutils NEWS                                    -*- 
outline -*-
   Note the use of single quotes, not double quotes.
   That creates files named xaa.xz, xab.xz and xac.xz.

-** Changes in behavior
+** Improvements

-  shuf will more efficiently output small subsets of large permutations.
-  For example `shuf -i1-$((2**32-1)) -n2` will no longer exhaust memory.
+  shuf outputs small subsets of large permutations much more efficiently.
+  For example `shuf -i1-$((2**32-1)) -n2` no longer exhausts memory.


 * Noteworthy changes in release 8.12 (2011-04-26) [stable]



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