Based on the output below, I think j, t, z are not what I would expect as per their C printf definition (assuming that is the goal). They should truncate values that do not fit in intmax_t, ptrdiff_t, size_t to the appropriate size (32 or 64-bit depending on architecture). I would certainly find that useful in FFI type extensions.

```
% set int64 0x8000000000000001
0x8000000000000001
% set int65 0x10000000000000000
0x10000000000000000
% foreach t {d u} {foreach s {{} j l ll t z I I32 I64} {puts "$s$t\t[format %$s$t $::int64] [format %$s$t $::int65]"}}
d       1 0
jd      9223372036854775809 18446744073709551616
ld      -9223372036854775807 0
lld     9223372036854775809 18446744073709551616
td      9223372036854775809 18446744073709551616
zd      9223372036854775809 18446744073709551616
Id      1 0
I32d    1 0
I64d    -9223372036854775807 0
u       1 0
ju      9223372036854775809 18446744073709551616
lu      9223372036854775809 0
llu     9223372036854775809 18446744073709551616
tu      9223372036854775809 18446744073709551616
zu      9223372036854775809 18446744073709551616
Iu      1 0
I32u    1 0
I64u    9223372036854775809 0
```