From f75ad2edcf3525597137a1c9da35e58ecd279e94 Mon Sep 17 00:00:00 2001
From: Yann Collet <cyan@fb.com>
Date: Fri, 25 Jan 2019 14:22:25 -0800
Subject: [PATCH] added ability to create timedFnState on stack

---
 programs/benchfn.c | 19 ++++++++++++++-----
 programs/benchfn.h | 17 ++++++++++++++++-
 2 files changed, 30 insertions(+), 6 deletions(-)

diff --git a/programs/benchfn.c b/programs/benchfn.c
index f5118d087..a27d91a07 100644
--- a/programs/benchfn.c
+++ b/programs/benchfn.c
@@ -148,7 +148,7 @@ BMK_runOutcome_t BMK_benchFunction(BMK_benchParams_t p,
 
         {   U64 const totalTime = UTIL_clockSpanNano(clockStart);
             BMK_runTime_t rt;
-            rt.nanoSecPerRun = totalTime / nbLoops;
+            rt.nanoSecPerRun = (double)totalTime / nbLoops;
             rt.sumOfReturn = dstSize;
             return BMK_setValid_runTime(rt);
     }   }
@@ -178,6 +178,15 @@ void BMK_freeTimedFnState(BMK_timedFnState_t* state) {
     free(state);
 }
 
+BMK_timedFnState_t* BMK_initStatic_timedFnState(void* buffer, size_t size, unsigned total_ms, unsigned run_ms)
+{
+    BMK_timedFnState_t* const r = (BMK_timedFnState_t*)buffer;
+    if (size < sizeof(struct BMK_timedFnState_s)) return NULL;
+    if ((size_t)buffer % 8) return NULL;  /* must be aligned on 8-bytes boundaries */
+    BMK_resetTimedFnState(r, total_ms, run_ms);
+    return r;
+}
+
 void BMK_resetTimedFnState(BMK_timedFnState_t* timedFnState, unsigned total_ms, unsigned run_ms)
 {
     if (!total_ms) total_ms = 1 ;
@@ -186,7 +195,7 @@ void BMK_resetTimedFnState(BMK_timedFnState_t* timedFnState, unsigned total_ms,
     timedFnState->timeSpent_ns = 0;
     timedFnState->timeBudget_ns = (U64)total_ms * TIMELOOP_NANOSEC / 1000;
     timedFnState->runBudget_ns = (U64)run_ms * TIMELOOP_NANOSEC / 1000;
-    timedFnState->fastestRun.nanoSecPerRun = (U64)(-1LL);
+    timedFnState->fastestRun.nanoSecPerRun = (double)TIMELOOP_NANOSEC * 2000000000;  /* hopefully large enough : must be larger than any potential measurement */
     timedFnState->fastestRun.sumOfReturn = (size_t)(-1LL);
     timedFnState->nbLoops = 1;
     timedFnState->coolTime = UTIL_getTime();
@@ -231,13 +240,13 @@ BMK_runOutcome_t BMK_benchTimedFn(BMK_timedFnState_t* cont,
         }
 
         {   BMK_runTime_t const newRunTime = BMK_extract_runTime(runResult);
-            U64 const loopDuration_ns = newRunTime.nanoSecPerRun * cont->nbLoops;
+            double const loopDuration_ns = newRunTime.nanoSecPerRun * cont->nbLoops;
 
-            cont->timeSpent_ns += loopDuration_ns;
+            cont->timeSpent_ns += (unsigned long long)loopDuration_ns;
 
             /* estimate nbLoops for next run to last approximately 1 second */
             if (loopDuration_ns > (runBudget_ns / 50)) {
-                U64 const fastestRun_ns = MIN(bestRunTime.nanoSecPerRun, newRunTime.nanoSecPerRun);
+                double const fastestRun_ns = MIN(bestRunTime.nanoSecPerRun, newRunTime.nanoSecPerRun);
                 cont->nbLoops = (U32)(runBudget_ns / fastestRun_ns) + 1;
             } else {
                 /* previous run was too short : blindly increase workload by x multiplier */
diff --git a/programs/benchfn.h b/programs/benchfn.h
index aa3c3e939..737dfa995 100644
--- a/programs/benchfn.h
+++ b/programs/benchfn.h
@@ -31,7 +31,7 @@ extern "C" {
 /* BMK_runTime_t: valid result return type */
 
 typedef struct {
-    unsigned long long nanoSecPerRun;  /* time per iteration (over all blocks) */
+    double nanoSecPerRun;  /* time per iteration (over all blocks) */
     size_t sumOfReturn;         /* sum of return values */
 } BMK_runTime_t;
 
@@ -160,6 +160,21 @@ void BMK_resetTimedFnState(BMK_timedFnState_t* timedFnState, unsigned total_ms,
 void BMK_freeTimedFnState(BMK_timedFnState_t* state);
 
 
+/* BMK_timedFnState_shell and BMK_initStatic_timedFnState() :
+ * Makes it possible to statically allocate a BMK_timedFnState_t on stack.
+ * BMK_timedFnState_shell is only there to allocate space,
+ * never ever access its members.
+ * BMK_timedFnState_t() actually accepts any buffer.
+ * It will check if provided buffer is large enough and is correctly aligned,
+ * and will return NULL if conditions are not respected.
+ */
+#define BMK_TIMEDFNSTATE_SIZE 56
+typedef union {
+    char never_access_space[BMK_TIMEDFNSTATE_SIZE];
+    long long alignment_enforcer;  /* must be aligned on 8-bytes boundaries */
+} BMK_timedFnState_shell;
+BMK_timedFnState_t* BMK_initStatic_timedFnState(void* buffer, size_t size, unsigned total_ms, unsigned run_ms);
+
 
 #endif   /* BENCH_FN_H_23876 */