This indicates that random() generates fewer random bits than rand(). Right ??

I don't think so. Looking at the produced values was a surprise.

Took the threads loop and ran it with 16 pids and 1024 random() calls. Used "%.64f" "%.72f" as format for the generated numbers. In most cases, different runs produce identical results.

<Update>
For completeness, here is the script.

#!/usr/bin/perl
use v5.030;
use threads;
use threads::shared;
use PDL;

BEGIN { $PDL::no_clone_skip_warning = 1; }

my $lock : shared = 0;

PDL::srand(3);  # PDL 2.087

for my $tid (1..16) {
    threads->create(sub {
        my $output = "";
        for (1..1024) {

            my $r = random();
            $output .= sprintf "%.72f\n", $r;
        }
        lock $lock;
        print $output;
    });
}

$_->join for threads->list;
[download]

</Update>

When a run produces a different result, I see two scenarios:

• One or two numbers are missing and are replaced by an already produced value. See examples 2 and 3 below.
• The generated numbers are significantly different. See example 4.

$ ./pdl-rand.pl | sort >sort.16384.1
$ ./pdl-rand.pl | sort >sort.16384.2
$ ./pdl-rand.pl | sort >sort.16384.3
$ ./pdl-rand.pl | sort >sort.16384.4

$ sort -u sort.16384.1 |wc -l
16384
$ sort -u sort.16384.2 |wc -l
16383
$ sort -u sort.16384.3 |wc -l
16382
$ sort -u sort.16384.4 |wc -l
16383

$ diff -U 1 sort.16384.1 sort.16384.2
--- sort.16384.1    2024-06-08 09:45:09.466739327 +0200
+++ sort.16384.2    2024-06-08 09:50:24.203356598 +0200
@@ -12562,2 +12562,3 @@
 0.7698795891537290048134423159353900700807571411132812500000000000000
+00000
+0.7698795891537290048134423159353900700807571411132812500000000000000
+00000
 0.7699350058887169945265327442029956728219985961914062500000000000000
+00000
@@ -14417,3 +14418,2 @@
 0.8818249357757870221519169717794284224510192871093750000000000000000
+00000
-0.8818467386417550013533173114410601556301116943359375000000000000000
+00000
 0.8818802323789649566521120505058206617832183837890625000000000000000
+00000

$ diff -U 1 sort.16384.1 sort.16384.3
--- sort.16384.1    2024-06-08 09:45:09.466739327 +0200
+++ sort.16384.3    2024-06-08 09:52:32.837243809 +0200
@@ -13113,2 +13113,3 @@
 0.8005079965106629558135864499490708112716674804687500000000000000000
+00000
+0.8005079965106629558135864499490708112716674804687500000000000000000
+00000
 0.8007896602698270083209308722871355712413787841796875000000000000000
+00000
@@ -13686,3 +13687,2 @@
 0.8361851909041919661547126452205702662467956542968750000000000000000
+00000
-0.8361968170640460273901339860458392649888992309570312500000000000000
+00000
 0.8364519442006479454931877626222558319568634033203125000000000000000
+00000
@@ -14417,3 +14417,2 @@
 0.8818249357757870221519169717794284224510192871093750000000000000000
+00000
-0.8818467386417550013533173114410601556301116943359375000000000000000
+00000
 0.8818802323789649566521120505058206617832183837890625000000000000000
+00000
@@ -16095,2 +16094,3 @@
 0.9834468387403769717991508514387533068656921386718750000000000000000
+00000
+0.9834468387403769717991508514387533068656921386718750000000000000000
+00000
 0.9837232694387190168328061190550215542316436767578125000000000000000
+00000

$ diff -U 1 sort.16384.1 sort.16384.4|head -12
--- sort.16384.1    2024-06-08 09:45:09.466739327 +0200
+++ sort.16384.4    2024-06-08 09:58:27.630459409 +0200
@@ -1,154 +1,161 @@
-0.0000798345195128779969639606917120033813262125477194786071777343750
+00000
+0.0000273717076871849010000561919220274376129964366555213928222656250
+00000
+0.0000550196742872266023331902229376311197484028525650501251220703125
+00000
 0.0001113510803039119965475445273028753945254720747470855712890625000
+00000
-0.0001282989599132870110840404231922207145544234663248062133789062500
+00000
 0.0002144808569095600127036443938166598854877520352602005004882812500
+00000
-0.0003265905868672370191731213484587215134524740278720855712890625000
+00000
 0.0003745585362475710206227319520877472314168699085712432861328125000
+00000
-0.0004606498956905009760365299342765865731053054332733154296875000000
+00000

$ diff -U 0 sort.16384.1 sort.16384.4|grep -v '@@'|wc -l
19698
[download]

I have no idea what's going on here but maybe someone else has.

Update: Fixed manually modified file names in diff output.

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