This is the in-place version: 
                Rate        split1       substr1         subst subst_i
+nplace
split1        2.93/s            --          -72%         -100%        
+ -100%
substr1       10.3/s          253%            --          -99%        
+  -99%
subst          901/s        30682%         8623%            --        
+  -24%
subst_inplace 1179/s        40176%        11313%           31%        
+    --
ok 1
ok 2
ok 3
1..3

[download]
code: 
sub subst_inplace
{
    my ($s1, $s2) = @_;

    use bytes;
    $$s1 =~ s/(\0)/substr $s2, $+[0]-1, 1/eg;
}

[download]

In reply to Re^2: Challenge: CPU-optimized byte-wise or-equals (for a meter of beer) by avar
in thread Challenge: CPU-optimized byte-wise or-equals (for a meter of beer) by dragonchild

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