HdrHistogram · fcostaoliveira · Sep 14, 2026 · Sep 15, 2026 · Sep 15, 2026
diff --git a/src/hdr_time.c b/src/hdr_time.c
@@ -5,6 +5,7 @@
 */
 
 #include <math.h>
+#include <limits.h>
 
 #include <hdr/hdr_time.h>
 
@@ -89,9 +90,21 @@ double hdr_timespec_as_double(const hdr_timespec* t)
 
 void hdr_timespec_from_double(hdr_timespec* t, double value)
 {
-    int seconds = (int) value;
-    int milliseconds = (int) round((value - seconds) * 1000);
+    /* tv_sec is a long on Windows; 2^(bits-1) is exact as a double and one past its max */
+    const double limit = ldexp(1.0, (int) (sizeof(long) * CHAR_BIT) - 1);
+    double seconds = trunc(value);
+    int milliseconds;
 
-    t->tv_sec = seconds;
+    /* converting a non-finite or out-of-range double to an integer is UB */
+    if (!isfinite(value) || seconds >= limit || seconds < -limit)
+    {
+        t->tv_sec = 0;
+        t->tv_nsec = 0;
+        return;
+    }
+
+    milliseconds = (int) round((value - seconds) * 1000);
+
+    t->tv_sec = (long) seconds;
     t->tv_nsec = milliseconds * 1000000;
 }
diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt
@@ -85,6 +85,8 @@ foreach(V 2.0.1.logV0 2.0.6.logV1 2.0.7S.logV2 2.0.7S.logV3)
     configure_file(jHiccup-${V}.hlog jHiccup-${V}.hlog COPYONLY)
 endforeach()
 
+configure_file(regression-log-start-time-overflow.hlog regression-log-start-time-overflow.hlog COPYONLY)
+
 foreach(V test_tagged_invalid_histogram.txt test_tagged_invalid_tag_key.txt test_tagged_invalid_timestamp.txt test_tagged_missing_histogram.txt)
     configure_file(${V} ${V} COPYONLY)
 endforeach()
diff --git a/test/hdr_histogram_log_test.c b/test/hdr_histogram_log_test.c
@@ -993,6 +993,30 @@ static int parse_line_from_file(const char* filename)
     return result;
 }
 
+/* A StartTime beyond int range must not be an out-of-range cast (UBSan). */
+static char* handle_wide_start_time(void)
+{
+    struct hdr_log_reader reader;
+    int rc;
+
+    FILE* f = fopen("regression-log-start-time-overflow.hlog", "r");
+    mu_assert("Can not open wide start time log", f != NULL);
+
+    hdr_log_reader_init(&reader);
+    rc = hdr_log_read_header(&reader, f);
+    fclose(f);
+
+    mu_assert("Failed to read header", compare_int(0, rc));
+    if (sizeof(reader.start_timestamp.tv_sec) >= 8)
+    {
+        mu_assert(
+            "Start time wrong",
+            compare_int64(INT64_C(1403476110183), (int64_t) reader.start_timestamp.tv_sec));
+    }
+
+    return 0;
+}
+
 static char* handle_invalid_log_lines(void)
 {
     mu_assert("Should have invalid histogram", -EINVAL == parse_line_from_file("test_tagged_invalid_histogram.txt"));
@@ -1106,6 +1130,7 @@ static struct mu_result all_tests(void)
     mu_run_test(decode_v1_log);
     mu_run_test(decode_v0_log);
     mu_run_test(handle_invalid_log_lines);
+    mu_run_test(handle_wide_start_time);
 
     mu_run_test(test_zig_zag_codec);
     mu_run_test(test_encode_and_decode_empty);

diff --git a/test/hdr_histogram_test.c b/test/hdr_histogram_test.c
@@ -11,8 +11,10 @@
 #include <string.h>
 
 #include <stdio.h>
+#include <math.h>
 #include <hdr/hdr_histogram.h>
 #include <hdr/hdr_interval_recorder.h>
+#include <hdr/hdr_time.h>
 
 #include "minunit.h"
 #include "hdr_test_util.h"
@@ -158,6 +160,51 @@ static char* test_invalid_init(void)
     return 0;
 }
 
+static char* test_timespec_from_double(void)
+{
+    hdr_timespec t;
+
+    hdr_timespec_from_double(&t, 1403476110.183);
+    mu_assert("seconds wrong", compare_int64(INT64_C(1403476110), (int64_t) t.tv_sec));
+    mu_assert("nanoseconds wrong", compare_int64(INT64_C(183000000), (int64_t) t.tv_nsec));
+
+    hdr_timespec_from_double(&t, -2.0);
+    mu_assert("negative seconds wrong", compare_int64(INT64_C(-2), (int64_t) t.tv_sec));
+    mu_assert("negative nanoseconds wrong", compare_int64(INT64_C(0), (int64_t) t.tv_nsec));
+
+    /* Exceeds int but fits a 64-bit long; reachable from a log header StartTime. */
+    hdr_timespec_from_double(&t, 1403476110183.0);
+    if (sizeof(long) >= 8)
+    {
+        mu_assert("wide seconds wrong", compare_int64(INT64_C(1403476110183), (int64_t) t.tv_sec));
+    }
+    else
+    {
+        mu_assert("unrepresentable seconds should be zeroed", compare_int64(INT64_C(0), (int64_t) t.tv_sec));
+    }
+    mu_assert("wide nanoseconds wrong", compare_int64(INT64_C(0), (int64_t) t.tv_nsec));
+
+    /* Values tv_sec cannot hold, and non-finite values, must not be converted. */
+    hdr_timespec_from_double(&t, 1e300);
+    mu_assert("huge seconds should be zeroed", compare_int64(INT64_C(0), (int64_t) t.tv_sec));
+    mu_assert("huge nanoseconds should be zeroed", compare_int64(INT64_C(0), (int64_t) t.tv_nsec));
+
+    hdr_timespec_from_double(&t, -1e300);
+    mu_assert("huge negative seconds should be zeroed", compare_int64(INT64_C(0), (int64_t) t.tv_sec));
+
+    hdr_timespec_from_double(&t, INFINITY);
+    mu_assert("inf seconds should be zeroed", compare_int64(INT64_C(0), (int64_t) t.tv_sec));
+
+    hdr_timespec_from_double(&t, -INFINITY);
+    mu_assert("-inf seconds should be zeroed", compare_int64(INT64_C(0), (int64_t) t.tv_sec));
+
+    hdr_timespec_from_double(&t, NAN);
+    mu_assert("nan seconds should be zeroed", compare_int64(INT64_C(0), (int64_t) t.tv_sec));
+    mu_assert("nan nanoseconds should be zeroed", compare_int64(INT64_C(0), (int64_t) t.tv_nsec));
+
+    return 0;
+}
+
 static char* test_bucket_config_shift_overflow(void)
 {
     struct hdr_histogram* h = NULL;
@@ -613,6 +660,7 @@ static struct mu_result all_tests(void)
 {
     mu_run_test(test_create);
     mu_run_test(test_invalid_init);
+    mu_run_test(test_timespec_from_double);
     mu_run_test(test_bucket_config_shift_overflow);
     mu_run_test(test_bucket_config_reject_defines_cfg);
     mu_run_test(test_create_with_large_values);

diff --git a/test/regression-log-start-time-overflow.hlog b/test/regression-log-start-time-overflow.hlog
@@ -0,0 +1,66 @@
+#[Logged with jHiccup version 2.0.7-SNAPSHOT]
+#[Histogram log format version 1.2]
+#[StartTime: 1403476110183.0 (seconds since epoch), Mon Jun 23 10:28:30 NZST 2014]
+"StartTimestamp","Interval_Length","Interval_Max","Interval_Compressed_Histogram"
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