Unbreak microbench, add os.now() (#93)

The removal of the high-precision but non-standard clock source in
commit 5af98ca broke microbench because Date.now() is not granular
enough for the benchmark runner to make forward progress.

This commit adds a new method to the os module that returns time
with microsecond precision.

quickjs-libc.c

@@ -1948,22 +1948,33 @@ static JSValue js_os_signal(JSContext *ctx, JSValueConst this_val,
 }
 
 #if defined(__linux__) || defined(__APPLE__)
-static int64_t get_time_ms(void)
+static int64_t get_time_us(void)
 {
     struct timespec ts;
     clock_gettime(CLOCK_MONOTONIC, &ts);
-    return (uint64_t)ts.tv_sec * 1000 + (ts.tv_nsec / 1000000);
+    return (int64_t)ts.tv_sec * 1000000 + (ts.tv_nsec / 1000);
 }
 #else
 /* more portable, but does not work if the date is updated */
-static int64_t get_time_ms(void)
+static int64_t get_time_us(void)
 {
     struct timeval tv;
     gettimeofday(&tv, NULL);
-    return (int64_t)tv.tv_sec * 1000 + (tv.tv_usec / 1000);
+    return (int64_t)tv.tv_sec * 1000000 + tv.tv_usec;
 }
 #endif
 
+static int64_t get_time_ms(void)
+{
+    return get_time_us() / 1000;
+}
+
+static JSValue js_os_now(JSContext *ctx, JSValueConst this_val,
+                         int argc, JSValueConst *argv)
+{
+    return JS_NewInt64(ctx, get_time_us());
+}
+
 static void unlink_timer(JSRuntime *rt, JSOSTimer *th)
 {
     if (th->link.prev) {
@@ -3606,6 +3617,7 @@ static const JSCFunctionListEntry js_os_funcs[] = {
     OS_FLAG(SIGTTIN),
     OS_FLAG(SIGTTOU),
 #endif
+    JS_CFUNC_DEF("now", 0, js_os_now ),
     JS_CFUNC_DEF("setTimeout", 2, js_os_setTimeout ),
     JS_CFUNC_DEF("clearTimeout", 1, js_os_clearTimeout ),
     JS_PROP_STRING_DEF("platform", OS_PLATFORM, 0 ),

tests/microbench.js

@@ -23,6 +23,7 @@
  * THE SOFTWARE.
  */
 import * as std from "std";
+import * as os from "os";
 
 function pad(str, n) {
     str += "";
@@ -97,7 +98,7 @@ var clocks_per_sec = 1000000;
 var max_iterations = 100;
 var clock_threshold = 2000;  /* favoring short measuring spans */
 var min_n_argument = 1;
-var get_clock = Date.now;
+var get_clock = os.now;
 
 function log_one(text, n, ti) {
     var ref;