From: Tels <nospam-abuse@bloodgate.com>
Date: Sat, 23 Oct 2004 16:56:31 +0000 (+0200)
Subject: Re: Devel::Peek: hash quality 125%?
X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=commitdiff_plain;h=d58892206344925510820a73d2d509d20abee418;p=p5sagit%2Fp5-mst-13.2.git

Re: Devel::Peek: hash quality 125%?
Message-Id: <200410231656.40995@bloodgate.com>

p4raw-id: //depot/perl@23419
---

diff --git a/ext/Devel/Peek/Changes b/ext/Devel/Peek/Changes
index e143f87..e87a7ca 100644
--- a/ext/Devel/Peek/Changes
+++ b/ext/Devel/Peek/Changes
@@ -62,3 +62,7 @@
 	Had problems with HEf_SVKEY magic.
 0.95:
 	Added "hash quality" output to estimate Perl's hash functions.
+
+1.02:
+	2004-10-22: Document "hash quality" output and update examples.
+
diff --git a/ext/Devel/Peek/Peek.pm b/ext/Devel/Peek/Peek.pm
index 4bd2dd9..4559a0d 100644
--- a/ext/Devel/Peek/Peek.pm
+++ b/ext/Devel/Peek/Peek.pm
@@ -3,7 +3,7 @@
 
 package Devel::Peek;
 
-$VERSION = '1.01';
+$VERSION = '1.02';
 $XS_VERSION = $VERSION;
 $VERSION = eval $VERSION;
 
@@ -391,29 +391,41 @@ The following shows the raw form of a reference to a hash.
 
 The output:
 
-        SV = RV(0xf041c)
-          REFCNT = 1
-          FLAGS = (ROK)
-          RV = 0xb2850
-        SV = PVHV(0xbd448)
-          REFCNT = 1
-          FLAGS = ()
-          NV = 0
-          ARRAY = 0xbd748
-          KEYS = 1
-          FILL = 1
-          MAX = 7
-          RITER = -1
-          EITER = 0x0
-        Elt "hello" => 0xbaaf0
-        SV = IV(0xbe860)
-          REFCNT = 1
-          FLAGS = (IOK,pIOK)
-          IV = 42
+	SV = RV(0x8177858) at 0x816a618
+	  REFCNT = 1
+	  FLAGS = (ROK)
+	  RV = 0x814fc10
+	  SV = PVHV(0x8167768) at 0x814fc10
+	    REFCNT = 1
+	    FLAGS = (SHAREKEYS)
+	    IV = 1
+	    NV = 0
+	    ARRAY = 0x816c5b8  (0:7, 1:1)
+	    hash quality = 100.0%
+	    KEYS = 1
+	    FILL = 1
+	    MAX = 7
+	    RITER = -1
+	    EITER = 0x0
+	    Elt "hello" HASH = 0xc8fd181b
+	    SV = IV(0x816c030) at 0x814fcf4
+	      REFCNT = 1
+	      FLAGS = (IOK,pIOK)
+	      IV = 42
 
 This shows C<$a> is a reference pointing to an SV.  That SV is a PVHV, a
 hash. Fields RITER and EITER are used by C<L<each>>.
 
+The "quality" of a hash is defined as the total number of comparisons needed
+to access every element once, relative to the expected number needed for a
+random hash. The value can go over 100%.
+
+The total number of comparisons is equal to the sum of the squares of the
+number of entries in each bucket.  For a random hash of C<<n>> keys into
+C<<k>> buckets, the expected value is:
+
+		n + n(n-1)/2k
+
 =head2 Dumping a large array or hash
 
 The C<Dump()> function, by default, dumps up to 4 elements from a