Add `nstime_ms_since` to get time since in ms

Milliseconds are used a lot in hpa, so it is convenient to have
`nstime_ms_since` function instead of dividing to `MILLION` constantly.

For consistency renamed `nstime_msec` to `nstime_ms` as `ms` abbreviation
is used much more commonly across codebase than `msec`.

```
$ grep -Rn '_msec' include src | wc -l
2

$ grep -RPn '_ms( |,|:)' include src | wc -l
72
```

Function `nstime_msec` wasn't used anywhere in the code yet.

include/jemalloc/internal/nstime.h

@@ -26,8 +26,8 @@ static const nstime_t nstime_zero = NSTIME_ZERO_INITIALIZER;
 void nstime_init(nstime_t *time, uint64_t ns);
 void nstime_init2(nstime_t *time, uint64_t sec, uint64_t nsec);
 uint64_t nstime_ns(const nstime_t *time);
+uint64_t nstime_ms(const nstime_t *time);
 uint64_t nstime_sec(const nstime_t *time);
-uint64_t nstime_msec(const nstime_t *time);
 uint64_t nstime_nsec(const nstime_t *time);
 void nstime_copy(nstime_t *time, const nstime_t *source);
 int nstime_compare(const nstime_t *a, const nstime_t *b);
@@ -39,6 +39,7 @@ void nstime_imultiply(nstime_t *time, uint64_t multiplier);
 void nstime_idivide(nstime_t *time, uint64_t divisor);
 uint64_t nstime_divide(const nstime_t *time, const nstime_t *divisor);
 uint64_t nstime_ns_since(const nstime_t *past);
+uint64_t nstime_ms_since(const nstime_t *past);
 
 typedef bool (nstime_monotonic_t)(void);
 extern nstime_monotonic_t *JET_MUTABLE nstime_monotonic;

src/hpa_hooks.c

@@ -59,5 +59,5 @@ hpa_hooks_curtime(nstime_t *r_nstime, bool first_reading) {
 
 static uint64_t
 hpa_hooks_ms_since(nstime_t *past_nstime) {
-	return nstime_ns_since(past_nstime) / 1000 / 1000;
+	return nstime_ms_since(past_nstime);
 }

src/nstime.c

@@ -63,7 +63,7 @@ nstime_ns(const nstime_t *time) {
 }
 
 uint64_t
-nstime_msec(const nstime_t *time) {
+nstime_ms(const nstime_t *time) {
 	nstime_assert_initialized(time);
 	return time->ns / MILLION;
 }
@@ -158,7 +158,7 @@ nstime_divide(const nstime_t *time, const nstime_t *divisor) {
 	return time->ns / divisor->ns;
 }
 
-/* Returns time since *past, w/o updating *past. */
+/* Returns time since *past in nanoseconds, w/o updating *past. */
 uint64_t
 nstime_ns_since(const nstime_t *past) {
 	nstime_assert_initialized(past);
@@ -171,6 +171,12 @@ nstime_ns_since(const nstime_t *past) {
 	return now.ns - past->ns;
 }
 
+/* Returns time since *past in milliseconds, w/o updating *past. */
+uint64_t
+nstime_ms_since(const nstime_t *past) {
+	return nstime_ns_since(past) / MILLION;
+}
+
 #ifdef _WIN32
 #  define NSTIME_MONOTONIC false
 static void

test/unit/nstime.c

@@ -228,6 +228,24 @@ TEST_BEGIN(test_nstime_ns_since) {
 }
 TEST_END
 
+TEST_BEGIN(test_nstime_ms_since) {
+	nstime_t delta;
+
+	nstime_init2(&delta, /* sec */ 1, /* nsec */ 0);
+	for (uint64_t i = 0; i < 10000; i++) {
+		nstime_t now;
+		nstime_init_update(&now);
+
+		nstime_t past;
+		nstime_copy(&past, &now);
+		nstime_subtract(&past, &delta);
+
+		expect_u64_ge(nstime_ms_since(&past), nstime_ms(&delta),
+		    "Incorrect time since result");
+	}
+}
+TEST_END
+
 TEST_BEGIN(test_nstime_monotonic) {
 	nstime_monotonic();
 }
@@ -248,5 +266,6 @@ main(void) {
 	    test_nstime_idivide,
 	    test_nstime_divide,
 	    test_nstime_ns_since,
+	    test_nstime_ms_since,
 	    test_nstime_monotonic);
 }