Make improvements

- Clean up sigaction() code
- Add a port scanner example
- Introduce a ParseCidr() API
- Clean up our futex abstraction code
- Fix a harmless integer overflow in ParseIp()
- Use kernel semaphores on NetBSD to make threads much faster

libc/calls/timeval_tomillis.c

@@ -0,0 +1,56 @@
+/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
+│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :vi│
+╞══════════════════════════════════════════════════════════════════════════════╡
+│ Copyright 2022 Justine Alexandra Roberts Tunney                              │
+│                                                                              │
+│ Permission to use, copy, modify, and/or distribute this software for         │
+│ any purpose with or without fee is hereby granted, provided that the         │
+│ above copyright notice and this permission notice appear in all copies.      │
+│                                                                              │
+│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
+│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
+│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
+│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
+│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
+│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
+│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
+│ PERFORMANCE OF THIS SOFTWARE.                                                │
+╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/calls/struct/timeval.h"
+#include "libc/limits.h"
+
+/**
+ * Reduces `ts` from 1e-6 to 1e-3 granularity w/ ceil rounding.
+ *
+ * This function returns the absolute number of milliseconds in a
+ * timeval. Ceiling rounding is used. For example, if `ts` is one
+ * nanosecond, then one millisecond will be returned. Ceil rounding is
+ * needed by many interfaces, e.g. setitimer(), because the zero
+ * timestamp has a valial meaning.
+ *
+ * This function also detects overflow in which case `INT64_MAX` or
+ * `INT64_MIN` may be returned. The `errno` variable isn't changed.
+ *
+ * @return 64-bit scalar milliseconds since epoch
+ */
+int64_t timeval_tomillis(struct timeval ts) {
+  int64_t ms;
+  // reduce precision from micros to millis
+  if (ts.tv_usec <= 999000) {
+    ts.tv_usec = (ts.tv_usec + 999) / 1000;
+  } else {
+    ts.tv_usec = 0;
+    if (ts.tv_sec < INT64_MAX) {
+      ts.tv_sec += 1;
+    }
+  }
+  // convert to scalar result
+  if (!__builtin_mul_overflow(ts.tv_sec, 1000ul, &ms) &&
+      !__builtin_add_overflow(ms, ts.tv_usec, &ms)) {
+    return ms;
+  } else if (ts.tv_sec < 0) {
+    return INT64_MIN;
+  } else {
+    return INT64_MAX;
+  }
+}