1 files changed, 72 insertions, 0 deletions
diff --git a/test/nxt_exp_approximation.c b/test/nxt_exp_approximation.c
new file mode 100644
index 00000000..1f79c068
--- /dev/null
+++ b/test/nxt_exp_approximation.c
@@ -0,0 +1,72 @@
+
+/*
+ * Copyright (C) Igor Sysoev
+ * Copyright (C) NGINX, Inc.
+ */
+
+#include <nxt_main.h>
+#include <math.h>
+
+
+nxt_int_t
+nxt_exp_approximation(nxt_thread_t *thr)
+{
+    double      n, e0, e1, diff;
+    nxt_nsec_t  start, end;
+
+    nxt_thread_time_update(thr);
+    nxt_log_error(NXT_LOG_NOTICE, thr->log,
+                  "exp approximation unit test started");
+
+    for (n = 0.0; n > -20.0; n -= 0.00001) {
+
+        e0 = nxt_event_conn_exponential_approximation(n);
+        e1 = exp(n);
+
+        diff = fabs(e0 - e1);
+
+        /* 0.028993 is max difference with libm exp(). */
+        if (diff > 0.028993) {
+            nxt_log_alert(thr->log,
+                          "exp approximation unit test failed: %0.6f %0.6f",
+                          n, diff);
+            return NXT_ERROR;
+        }
+    }
+
+
+    nxt_thread_time_update(thr);
+    start = nxt_thread_monotonic_time(thr);
+
+    e0 = 0;
+    for (n = 0.0; n > -20.0; n -= 0.00001) {
+        e0 += nxt_event_conn_exponential_approximation(n);
+    }
+
+    nxt_thread_time_update(thr);
+    end = nxt_thread_monotonic_time(thr);
+
+    /* e0 is passed but not output to eliminate optimization. */
+    nxt_log_error(NXT_LOG_NOTICE, thr->log, "exp approximation: %0.1fns",
+                  (end - start) / 20000000.0, e0);
+
+
+    nxt_thread_time_update(thr);
+    start = nxt_thread_monotonic_time(thr);
+
+    e0 = 0;
+    for (n = 0.0; n > -20.0; n -= 0.000001) {
+        e0 += exp(n);
+    }
+
+    nxt_thread_time_update(thr);
+    end = nxt_thread_monotonic_time(thr);
+
+    /* e0 is passed but not output to eliminate optimization. */
+    nxt_log_error(NXT_LOG_NOTICE, thr->log, "libm exp(): %0.1fns",
+                  (end - start) / 20000000.0, e0);
+
+    nxt_log_error(NXT_LOG_NOTICE, thr->log,
+                  "exp approximation unit test passed");
+    return NXT_OK;
+}