sx/issues/0090-int-formatter-extremes.md

0090 — integer formatter can't render i64::MIN or unsigned all-ones

STATUS: RESOLVED (F0.8). Both extremes now render correctly: s64.min → -9223372036854775808, u64.max → 18446744073709551615.

Root cause.

• Symptom 1 (i64::MIN): std.int_to_string computed the magnitude as 0 - n, which overflows for s64::MIN (its magnitude is unrepresentable as a positive s64) — the value stayed negative, the while v > 0 loop ran zero times, and only the - was emitted.
• Symptom 2 (unsigned all-ones): any_to_string's case int: arm formatted every integer as s64 (int_to_string(xx val)); there was no way to tell a u64 from an s64, so an all-ones u64 printed as -1.

Fix per file.

• library/modules/std.sx — int_to_string now extracts digits straight from n (taking |n % 10| per digit, n truncates toward zero) so it never negates s64::MIN. Added uint_to_string (unsigned decimal via long-division-by-10 over four 16-bit limbs) and decompose_u16x4 (the shared 16-bit-limb split, now reused by int_to_hex_string too). any_to_string's case int: routes through the new type_is_unsigned(type) query to pick the unsigned vs signed formatter. Declared type_is_unsigned :: ($T: Type) -> bool #builtin;.
• src/ir/types.zig — TypeTable.isUnsignedInt (canonical signedness predicate; single source of truth).
• src/ir/inst.zig — type_is_unsigned BuiltinId.
• src/ir/calls.zig — register type_is_unsigned as a .bool reflection builtin.
• src/ir/lower.zig — tryLowerReflectionCall arm: static fold + dynamic callBuiltin.
• src/ir/interp.zig — interp arm (reads the boxed TypeId / type_of aggregate shape).
• src/ir/emit_llvm.zig + src/backend/llvm/reflection.zig + src/backend/llvm/ops.zig — lazy [N x i1] __sx_type_is_unsigned table built from isUnsignedInt; runtime arm GEPs in at the TypeId.

Regression test. examples/0046-basic-int-formatter-extremes.sx pins both extremes plus a width spread (s8/s16/s32 + u8/u16/u32/u64, mins/maxes, 0, ordinary values). Unit tests: isUnsignedInt in src/ir/types.test.zig.

STATUS (original): OPEN. Pre-existing + orthogonal; surfaced (not introduced) by NL.1. Manager-verified independent of the numeric-limit accessors. Scheduled separately.

Symptom

print("{}", x) mis-renders the integer extremes the s64-based formatter can't represent:

• i64::MIN (-9223372036854775808) prints a bare - (the minus sign with NO digits).
• An unsigned all-ones value (e.g. u64.max = 18446744073709551615) prints -1 (the i64 bit-reinterpretation), not the unsigned decimal.

Reproduction (no numeric-limit accessor needed — pre-existing)

#import "modules/std.sx";
main :: () {
    x := -9223372036854775807 - 1;   // i64::MIN
    print("min={}\n", x);            // prints "min=-"  (should be -9223372036854775808)
}

u64.max (via the NL.1 accessor, or any all-ones u64) prints -1 for the same root reason.

Root cause (suspected)

The integer-to-string path is s64-based (std.int_to_string / the {} formatter takes s64): it negates the value to print the sign, but -i64::MIN overflows, and it has no unsigned-aware path so an all-ones u64 is read as -1. Needs a width/ signedness-aware integer formatter (format by the value's actual integer TYPE: unsigned types print the unsigned decimal; signed MIN is handled without negating).

Investigation prompt

Make the {} integer formatter type-aware: render an unsigned integer as its unsigned decimal (all 64 bits for u64), and handle signed MIN without the -MIN overflow (e.g. format the magnitude via unsigned arithmetic, or special-case MIN). Verify: i64::MIN prints -9223372036854775808; u64.max prints 18446744073709551615; existing numeric output (incl. the NL.1 examples, which assert via bit-reinterpret) stays green. Likely area: the formatter / int_to_string in the std print path and/or the comptime {} lowering.