# Step: stdlib — Strings additions, SysClock, more Math

Tag `v3-stdlib-more`. Suite **151/151**; fixpoint **OK**
(image **2,337,882 bytes**).

## `Strings`

- **`Slice(s, start, stop, dst)`** — Python-style `s[start:stop]`:
  0-based, negative indices count from the end (`-1` = last),
  `stop` is exclusive, both clamp to `[0, Length]`; the result is
  truncated to `dst`'s capacity.  (`"Hello, World"[0:5]` → `Hello`,
  `[-5:12]` → `World`, `[0:-8]` → `Hell`, `[3:3]` → `""`.)
- **`Insert(src, dst, pos)`** — inserts `src` at 0-based `pos`
  (clamped), truncated to `dst`'s capacity.
- **`Replace(src, dst, pos)`** — overwrites `dst` from `pos` with
  `src`, extending (and re-terminating) if it runs past the old end.
- **`Capitalize(s)`** — first character upper, the rest lower (ASCII).

## `SysClock` (new)

- `Time() : LONGINT` — seconds since the Unix epoch.
- `Clock() : LONGINT` — processor time in ticks,
  `ClocksPerSec = 1000000`.
- Bound to shim `m2time`/`m2clock` (libc `time`/`clock`); the shim
  gained `#include <time.h>` and the two functions.

## `Math`

Added: `log10`, `atan2`, `sinh`, `cosh`, `tanh`, `hypot`, `floor`,
`ceil`, `trunc`, `round`, `fmod` (all bound to libm).

## Tests

- `strings_slice_prog.mod` (255): `Slice` (incl. negatives and empty),
  `Insert`, `Replace`, `Capitalize`.
- `math2_prog.mod` (31): `hypot`/`floor`/`ceil`/`trunc`/`log10`.
- `sysclock_prog.mod` (3): `Time` after 2020, `Clock` >= 0.

## Files

`stdlib/strings.def`/`.mod`, `stdlib/sysclock.def`/`.mod`,
`stdlib/math.def`/`.mod`, `runtime/syslib/shim.c`,
`compiler/tests/{strings_slice_prog,math2_prog,sysclock_prog}.mod`,
`compiler/run_tests.sh`, `docs/features.md`.