Make SANDGLASS_REALTICKS accurate to 1 clock cycle.

2 files changed, 15 insertions, 5 deletions

diff --git a/src/sandglass.c b/src/sandglass.c
index c3435d0..b9316e5 100644
--- a/src/sandglass.c
+++ b/src/sandglass.c
@@ -179,15 +179,25 @@ int
 sandglass_elapse(sandglass_t *sandglass)
 {
   long oldgrains = sandglass->grains;
+  sandglass_t baseline;
 
   if (sandglass_real_gettime(sandglass) != 0)
     return -1;
 
   sandglass->grains -= oldgrains;
-  /* Magical correction for timespec-based grains */
   if (sandglass->grains < 0)
+    /* Magical correction for timespec-based grains */
     sandglass->grains += sandglass->adjustment;
-  sandglass->grains /= sandglass->loops;
+
+  if (sandglass->attributes.resolution == SANDGLASS_REALTICKS) {
+    baseline.attributes.incrementation = SANDGLASS_MONOTONIC;
+    baseline.attributes.resolution     = SANDGLASS_CPUTIME;
+    baseline.loops = sandglass->loops;
+
+    sandglass_bench(&baseline, { });
+    sandglass->grains -= baseline.grains;
+    sandglass->grains /= sandglass->loops;
+  }
 
   return 0;
 }
diff --git a/tests/monotonic-realticks.c b/tests/monotonic-realticks.c
index 119b3bb..eb9e9f6 100644
--- a/tests/monotonic-realticks.c
+++ b/tests/monotonic-realticks.c
@@ -30,16 +30,16 @@ main()
 {
   sandglass_t sandglass;
   sandglass_attributes_t attr = { SANDGLASS_MONOTONIC, SANDGLASS_REALTICKS };
-  struct timespec tosleep = { .tv_sec = 0, .tv_nsec = 111111111L };
+  unsigned int i = 0;
 
   if (sandglass_create(&sandglass, &attr, &attr) != 0) {
     perror("sandglass_create()");
     return EXIT_FAILURE;
   }
 
-  sandglass_bench(&sandglass, sandglass_spin(&tosleep));
+  sandglass_bench(&sandglass, ++i);
 
-  printf("%g\n", sandglass.grains/sandglass.resolution);
+  printf("%ld\n", sandglass.grains);
 
   return EXIT_SUCCESS;
 }