Weird truncation with printf %g

[stephane-chazelas]

$ ksh -c 'printf "%.30g\n" 1e{10..31}'
10000000000
100000000000
1000000000000
10000000000000
100000000000000
1000000000000000
10000000000000000
100000000000000000
100000000000000000
100000000000000000
100000000000000000
100000000000000000
100000000000000000
100000000000000000
100000000000000000
100000000000000000
100000000000000000
100000000000000000
100000000000000000
100000000000000000
1e+30
1e+31

Same with typeset -E:

$ ksh -c 'typeset -E30 i; for i in 1e{10..31}; do print "$i"; done'
10000000000
100000000000
1000000000000
10000000000000
100000000000000
100000000000000
100000000000000
100000000000000
100000000000000
100000000000000
100000000000000
100000000000000
100000000000000
100000000000000
100000000000000
100000000000000
100000000000000
100000000000000
100000000000000
100000000000000
1e+30
1e+31

With both:

$ ksh --version
  version         sh (AT&T Research) 93u+m/1.0.10 2024-08-01

on Debian testing amd64 and current git head:

$ ksh --version
  version         sh (AT&T Research) 93u+m/1.1.0-alpha+de24bb01 2026-03-23

[hyenias]

aarch64 GNU/Linux with 128bit long doubles:

$ ksh -c 'printf "%.30g\n" 1e{10..31}'
10000000000
100000000000
1000000000000
10000000000000
100000000000000
1000000000000000
10000000000000000
100000000000000000
1000000000000000000
10000000000000000000
100000000000000000000
1000000000000000000000
10000000000000000000000
100000000000000000000000
1000000000000000000000000
10000000000000000000000000
100000000000000000000000000
1000000000000000000000000000
10000000000000000000000000000
100000000000000000000000000000
1e+30
1e+31

Here I go from my 128bit long double to a 64bit double:

$ ksh -c 'typeset -E30 i; for i in 1e{10..31}; do print "$i"; done'
10000000000
100000000000
1000000000000
10000000000000
100000000000000
100000000000000
100000000000000
100000000000000
100000000000000
100000000000000
100000000000000
100000000000000
100000000000000
100000000000000
100000000000000
100000000000000
100000000000000
100000000000000
100000000000000
100000000000000
1e+30
1e+31

Food for thought:

$ ksh -c 'typeset -E i; for i in 1e{10..31}; do echo $i: $((i)); done'
1e+10: 10000000000
1e+11: 100000000000
1e+12: 1000000000000
1e+13: 10000000000000
1e+14: 100000000000000
1e+15: 1000000000000000
1e+16: 10000000000000000
1e+17: 100000000000000000
1e+18: 1000000000000000000
1e+19: 10000000000000000000
1e+20: 100000000000000000000
1e+21: 1000000000000000000000
1e+22: 10000000000000000000000
1e+23: 99999999999999991611392
1e+24: 999999999999999983222784
1e+25: 10000000000000000905969664
1e+26: 100000000000000004764729344
1e+27: 1000000000000000013287555072
1e+28: 9999999999999999583119736832
1e+29: 99999999999999991433150857216
1e+30: 1000000000000000019884624838656
1e+31: 9999999999999999635896294965248

$ ksh -c 'typeset -lE i; for i in 1e{10..31}; do echo $i: $((i)); done'
1e+10: 10000000000
1e+11: 100000000000
1e+12: 1000000000000
1e+13: 10000000000000
1e+14: 100000000000000
1e+15: 1000000000000000
1e+16: 10000000000000000
1e+17: 100000000000000000
1e+18: 1000000000000000000
1e+19: 10000000000000000000
1e+20: 100000000000000000000
1e+21: 1000000000000000000000
1e+22: 10000000000000000000000
1e+23: 100000000000000000000000
1e+24: 1000000000000000000000000
1e+25: 10000000000000000000000000
1e+26: 100000000000000000000000000
1e+27: 1000000000000000000000000000
1e+28: 10000000000000000000000000000
1e+29: 100000000000000000000000000000
1e+30: 1000000000000000000000000000000
1e+31: 10000000000000000000000000000000