crtl: asctime / ctime / timegm

• Type: feature (gap) — Track B (lib/crtl/src/time.c, include/time.h)
• Status: done
• Opened / closed: 2026-08-05
• Found by: tools/gcc_diff_probe.sh, third case batch ([[feature-c-gcc-oracle-differential-probe]]).

Five functions were missing outright — asctime, asctime_r, ctime, ctime_r, timegm. ctime(&t) is the shortest way to print a time in C, so this is a gap real code hits immediately; it failed at compile time ("call to undeclared function"), which is the good failure mode, but it failed.

Implementation notes

• asctime's layout is fixed by the standard (C99 7.23.3.1): "Www Mmm dd hh:mm:ss yyyy\n", 26 bytes with the NUL, mday space-padded and the time fields zero-padded. Written out literally rather than through strftime, which has no "%e inside a fixed layout" form that would give the space padding. Verified byte-identical to gcc for t = 1000000000: Sun Sep 9 01:46:40 2001 — note the two spaces before the 9, which is exactly the part a %d-based version gets wrong.
• timegm is mktime — crtl's mktime is already UTC (there is no local-time offset in the PAL, and its own comment says "best-effort, UTC"). It exists under its own name because code that means UTC should not have to depend on mktime happening to be; if a real local-time offset ever lands, timegm is the one that must not follow it.
• asctime/ctime use one static buffer, as specified; the _r forms take the caller's.

Gate

gcc_diff_probe cases ctime-asctime-shape and timegm-roundtrip byte-match gcc; clean on native/i386/arm32/aarch64. gate.sh lib green, c-testsuite 219/0/1.