##
<#> gv[*b] s # $b[$i]
<1> rv2av sKR/1
<0> padsv[$i:2,3] s
<2> aelem sK/2
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<0> padsv[$b:3,4] s # $b
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my $b = $b[$i]; ... $b ... $b ... $b # 6 + 1*3 = 9 ops
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$b[$i] ... $b[$i] ... $b[$i]; # 0 + 4*3 = 12 ops