ref_time_ticks: normalize to nanoseconds on every platform

doc/source/stdlib/handmade/function-builtin-ref_time_ticks-0xc4aeadf4dce1cb3f.rst

@@ -1 +1 @@
-Captures the current high-resolution time in ticks, suitable for measuring elapsed intervals with `get_time_usec`.
+Returns a monotonic timestamp in nanoseconds since an unspecified epoch (the same epoch within a process; not comparable across processes or reboots). Use with `get_time_usec(ref)` / `get_time_nsec(ref)` for elapsed-interval math; raw subtraction `now - then` is also valid since the unit is always nanoseconds on every platform.

src/hal/performance_time.cpp

@@ -15,36 +15,71 @@ namespace das {
 
 #endif
 
+// ref_time_ticks() returns CLOCK_MONOTONIC-style nanoseconds on every platform.
+// Prior to this normalization, Windows returned raw QueryPerformanceCounter
+// ticks (~10 MHz typical) while Linux/macOS already returned ns — so callers
+// that did `ref_time_ticks() + int64(timeout_sec * 1_000_000)` got 30 s on
+// Windows (lucky math at 10 MHz) but 30 ms on POSIX. The footgun is gone: raw
+// subtraction `now - then` always yields nanoseconds elapsed.
+//
+// Prefer `get_time_usec(start)` / `get_time_nsec(start)` for elapsed-time
+// comparisons — those wrap the subtraction and continue to work portably.
+
 #ifdef _MSC_VER
 
 #define WIN32_LEAN_AND_MEAN
 #include <windows.h>
 
+// QueryPerformanceFrequency is invariant after boot — cache once per process
+// to avoid a syscall on every ref_time_ticks() call. Race-tolerant: parallel
+// initialisers all compute the same value, and int64 stores are atomic on
+// x64/arm64.
+//
+// We also precompute `qpc_ns_per_tick = 1e9 / freq` when it divides cleanly
+// (the universal Win 7+ case where QPF = 10 MHz → 100 ns/tick). The fast path
+// is one multiply per call, so ref_time_ticks() stays within ~1 ns of the
+// bare QueryPerformanceCounter cost — critical for the function profiler,
+// which brackets every call. Fallback split path handles non-divisible
+// frequencies (theoretical; not observed on modern Windows).
+static int64_t qpc_ns_per_tick = 0;     // 0 -> use the fallback split path
+
+static int64_t qpc_freq() {
+    static int64_t cached = 0;
+    if ( cached == 0 ) {
+        LARGE_INTEGER f;
+        QueryPerformanceFrequency(&f);
+        cached = f.QuadPart;
+        qpc_ns_per_tick = (1000000000LL % cached == 0) ? (1000000000LL / cached) : 0;
+    }
+    return cached;
+}
+
 extern "C" int64_t ref_time_ticks () {
-    LARGE_INTEGER  t0;
+    LARGE_INTEGER t0;
     QueryPerformanceCounter(&t0);
-    return t0.QuadPart;
+    const int64_t freq = qpc_freq();
+    if ( qpc_ns_per_tick ) {
+        return t0.QuadPart * qpc_ns_per_tick;
+    }
+    // Fallback: convert QPC counter to nanoseconds without overflowing int64:
+    //   ns = (ticks / freq) * 1e9 + (ticks % freq) * 1e9 / freq
+    // freq is typically 10 MHz, so (ticks / freq) fits comfortably and the
+    // remainder * 1e9 also fits (max ~1e16, well under 2^63).
+    const int64_t whole = t0.QuadPart / freq;
+    const int64_t rem   = t0.QuadPart % freq;
+    return whole * 1000000000LL + (rem * 1000000000LL) / freq;
 }
 
 extern "C" int get_time_usec ( int64_t reft ) {
-    int64_t t0 = ref_time_ticks();
-    LARGE_INTEGER freq;
-    QueryPerformanceFrequency(&freq);
-    return int((t0-reft)*1000000LL/freq.QuadPart);
+    return int((ref_time_ticks() - reft) / 1000LL);
 }
 
 extern "C" int64_t get_time_nsec ( int64_t reft ) {
-    int64_t t0 = ref_time_ticks();
-    LARGE_INTEGER freq;
-    QueryPerformanceFrequency(&freq);
-    return  int64_t((t0-reft)*1000000000LL/freq.QuadPart);
+    return ref_time_ticks() - reft;
 }
 
-extern "C" int64_t ref_time_delta_to_usec(int64_t ref)
-{
-    LARGE_INTEGER freq;
-    QueryPerformanceCounter(&freq);
-    return ref * 1000000LL/freq.QuadPart;
+extern "C" int64_t ref_time_delta_to_usec ( int64_t ref ) {
+    return ref / 1000LL;
 }
 
 #elif __linux__ || defined(_EMSCRIPTEN_VER) || defined __HAIKU__
@@ -59,37 +94,36 @@ extern "C" int64_t ref_time_ticks () {
         DAS_ASSERT(false);
         return -1;
     }
-
     return ts.tv_sec * NSEC_IN_SEC + ts.tv_nsec;
 }
 
 extern "C" int get_time_usec ( int64_t reft ) {
-    return int((ref_time_ticks() - reft) / (NSEC_IN_SEC/1000000LL));
+    return int((ref_time_ticks() - reft) / 1000LL);
 }
 
 extern "C" int64_t get_time_nsec ( int64_t reft ) {
-    return  ref_time_ticks() - reft;
+    return ref_time_ticks() - reft;
 }
 
-extern "C" int64_t ref_time_delta_to_usec(int64_t ref) { return ref / (NSEC_IN_SEC/1000000LL); }
+extern "C" int64_t ref_time_delta_to_usec ( int64_t ref ) { return ref / 1000LL; }
 
 
 #else // osx
 
 #include <time.h>
 
-extern "C" int64_t ref_time_ticks() {
+extern "C" int64_t ref_time_ticks () {
     return clock_gettime_nsec_np(CLOCK_MONOTONIC_RAW);
 }
 
 extern "C" int get_time_usec ( int64_t reft ) {
-    return (clock_gettime_nsec_np(CLOCK_MONOTONIC_RAW) - reft)/1000LL;
+    return int((ref_time_ticks() - reft) / 1000LL);
 }
 
 extern "C" int64_t get_time_nsec ( int64_t reft ) {
-    return clock_gettime_nsec_np(CLOCK_MONOTONIC_RAW) - reft;
+    return ref_time_ticks() - reft;
 }
 
-extern "C" int64_t ref_time_delta_to_usec(int64_t ref) { return ref / 1000LL; }
+extern "C" int64_t ref_time_delta_to_usec ( int64_t ref ) { return ref / 1000LL; }
 
 #endif