diff --git a/generated_for_cmake/upb/json/parser.c b/generated_for_cmake/upb/json/parser.c
index ca018f4c0f..1423add9c5 100644
--- a/generated_for_cmake/upb/json/parser.c
+++ b/generated_for_cmake/upb/json/parser.c
@@ -1696,24 +1696,15 @@ static void start_timestamp_zone(upb_json_parser *p, const char *ptr) {
   capture_begin(p, ptr);
 }
 
-static int div_round_up2(int n, int d) {
-  return (n + d - 1) / d;
-}
-
 /* epoch_days(1970, 1, 1) == 1970-01-01 == 0. */
 static int epoch_days(int year, int month, int day) {
   static const uint16_t month_yday[12] = {0,   31,  59,  90,  120, 151,
                                           181, 212, 243, 273, 304, 334};
-  int febs_since_0 = month > 2 ? year + 1 : year;
-  int leap_days_since_0 = div_round_up2(febs_since_0, 4) -
-                          div_round_up2(febs_since_0, 100) +
-                          div_round_up2(febs_since_0, 400);
-  int days_since_0 =
-      365 * year + month_yday[month - 1] + (day - 1) + leap_days_since_0;
-
-  /* Convert from 0-epoch (0001-01-01 BC) to Unix Epoch (1970-01-01 AD).
-   * Since the "BC" system does not have a year zero, 1 BC == year zero. */
-  return days_since_0 - 719528;
+  uint32_t year_adj = year + 4800;  /* Ensure positive year, multiple of 400. */
+  uint32_t febs = year_adj - (month <= 2 ? 1 : 0);  /* Februaries since base. */
+  uint32_t leap_days = 1 + (febs / 4) - (febs / 100) + (febs / 400);
+  uint32_t days = 365 * year_adj + leap_days + month_yday[month - 1] + day - 1;
+  return days - 2472692;  /* Adjust to Unix epoch. */
 }
 
 static int64_t upb_timegm(const struct tm *tp) {
@@ -2582,11 +2573,11 @@ static bool does_fieldmask_end(upb_json_parser *p) {
  * final state once, when the closing '"' is seen. */
 
 
-#line 2787 "upb/json/parser.rl"
+#line 2778 "upb/json/parser.rl"
 
 
 
-#line 2590 "upb/json/parser.c"
+#line 2581 "upb/json/parser.c"
 static const char _json_actions[] = {
 	0, 1, 0, 1, 1, 1, 3, 1, 
 	4, 1, 6, 1, 7, 1, 8, 1, 
@@ -2841,7 +2832,7 @@ static const int json_en_value_machine = 78;
 static const int json_en_main = 1;
 
 
-#line 2790 "upb/json/parser.rl"
+#line 2781 "upb/json/parser.rl"
 
 size_t parse(void *closure, const void *hd, const char *buf, size_t size,
              const upb_bufhandle *handle) {
@@ -2864,7 +2855,7 @@ size_t parse(void *closure, const void *hd, const char *buf, size_t size,
   capture_resume(parser, buf);
 
   
-#line 2868 "upb/json/parser.c"
+#line 2859 "upb/json/parser.c"
 	{
 	int _klen;
 	unsigned int _trans;
@@ -2939,147 +2930,147 @@ _match:
 		switch ( *_acts++ )
 		{
 	case 1:
-#line 2595 "upb/json/parser.rl"
+#line 2586 "upb/json/parser.rl"
 	{ p--; {cs = stack[--top]; goto _again;} }
 	break;
 	case 2:
-#line 2597 "upb/json/parser.rl"
+#line 2588 "upb/json/parser.rl"
 	{ p--; {stack[top++] = cs; cs = 23;goto _again;} }
 	break;
 	case 3:
-#line 2601 "upb/json/parser.rl"
+#line 2592 "upb/json/parser.rl"
 	{ start_text(parser, p); }
 	break;
 	case 4:
-#line 2602 "upb/json/parser.rl"
+#line 2593 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_text(parser, p)); }
 	break;
 	case 5:
-#line 2608 "upb/json/parser.rl"
+#line 2599 "upb/json/parser.rl"
 	{ start_hex(parser); }
 	break;
 	case 6:
-#line 2609 "upb/json/parser.rl"
+#line 2600 "upb/json/parser.rl"
 	{ hexdigit(parser, p); }
 	break;
 	case 7:
-#line 2610 "upb/json/parser.rl"
+#line 2601 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_hex(parser)); }
 	break;
 	case 8:
-#line 2616 "upb/json/parser.rl"
+#line 2607 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(escape(parser, p)); }
 	break;
 	case 9:
-#line 2622 "upb/json/parser.rl"
+#line 2613 "upb/json/parser.rl"
 	{ p--; {cs = stack[--top]; goto _again;} }
 	break;
 	case 10:
-#line 2627 "upb/json/parser.rl"
+#line 2618 "upb/json/parser.rl"
 	{ start_year(parser, p); }
 	break;
 	case 11:
-#line 2628 "upb/json/parser.rl"
+#line 2619 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_year(parser, p)); }
 	break;
 	case 12:
-#line 2632 "upb/json/parser.rl"
+#line 2623 "upb/json/parser.rl"
 	{ start_month(parser, p); }
 	break;
 	case 13:
-#line 2633 "upb/json/parser.rl"
+#line 2624 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_month(parser, p)); }
 	break;
 	case 14:
-#line 2637 "upb/json/parser.rl"
+#line 2628 "upb/json/parser.rl"
 	{ start_day(parser, p); }
 	break;
 	case 15:
-#line 2638 "upb/json/parser.rl"
+#line 2629 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_day(parser, p)); }
 	break;
 	case 16:
-#line 2642 "upb/json/parser.rl"
+#line 2633 "upb/json/parser.rl"
 	{ start_hour(parser, p); }
 	break;
 	case 17:
-#line 2643 "upb/json/parser.rl"
+#line 2634 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_hour(parser, p)); }
 	break;
 	case 18:
-#line 2647 "upb/json/parser.rl"
+#line 2638 "upb/json/parser.rl"
 	{ start_minute(parser, p); }
 	break;
 	case 19:
-#line 2648 "upb/json/parser.rl"
+#line 2639 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_minute(parser, p)); }
 	break;
 	case 20:
-#line 2652 "upb/json/parser.rl"
+#line 2643 "upb/json/parser.rl"
 	{ start_second(parser, p); }
 	break;
 	case 21:
-#line 2653 "upb/json/parser.rl"
+#line 2644 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_second(parser, p)); }
 	break;
 	case 22:
-#line 2658 "upb/json/parser.rl"
+#line 2649 "upb/json/parser.rl"
 	{ start_duration_base(parser, p); }
 	break;
 	case 23:
-#line 2659 "upb/json/parser.rl"
+#line 2650 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_duration_base(parser, p)); }
 	break;
 	case 24:
-#line 2661 "upb/json/parser.rl"
+#line 2652 "upb/json/parser.rl"
 	{ p--; {cs = stack[--top]; goto _again;} }
 	break;
 	case 25:
-#line 2666 "upb/json/parser.rl"
+#line 2657 "upb/json/parser.rl"
 	{ start_timestamp_base(parser); }
 	break;
 	case 26:
-#line 2668 "upb/json/parser.rl"
+#line 2659 "upb/json/parser.rl"
 	{ start_timestamp_fraction(parser, p); }
 	break;
 	case 27:
-#line 2669 "upb/json/parser.rl"
+#line 2660 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_timestamp_fraction(parser, p)); }
 	break;
 	case 28:
-#line 2671 "upb/json/parser.rl"
+#line 2662 "upb/json/parser.rl"
 	{ start_timestamp_zone(parser, p); }
 	break;
 	case 29:
-#line 2672 "upb/json/parser.rl"
+#line 2663 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_timestamp_zone(parser, p)); }
 	break;
 	case 30:
-#line 2674 "upb/json/parser.rl"
+#line 2665 "upb/json/parser.rl"
 	{ p--; {cs = stack[--top]; goto _again;} }
 	break;
 	case 31:
-#line 2679 "upb/json/parser.rl"
+#line 2670 "upb/json/parser.rl"
 	{ start_fieldmask_path_text(parser, p); }
 	break;
 	case 32:
-#line 2680 "upb/json/parser.rl"
+#line 2671 "upb/json/parser.rl"
 	{ end_fieldmask_path_text(parser, p); }
 	break;
 	case 33:
-#line 2685 "upb/json/parser.rl"
+#line 2676 "upb/json/parser.rl"
 	{ start_fieldmask_path(parser); }
 	break;
 	case 34:
-#line 2686 "upb/json/parser.rl"
+#line 2677 "upb/json/parser.rl"
 	{ end_fieldmask_path(parser); }
 	break;
 	case 35:
-#line 2692 "upb/json/parser.rl"
+#line 2683 "upb/json/parser.rl"
 	{ p--; {cs = stack[--top]; goto _again;} }
 	break;
 	case 36:
-#line 2697 "upb/json/parser.rl"
+#line 2688 "upb/json/parser.rl"
 	{
         if (is_wellknown_msg(parser, UPB_WELLKNOWN_TIMESTAMP)) {
           {stack[top++] = cs; cs = 47;goto _again;}
@@ -3093,11 +3084,11 @@ _match:
       }
 	break;
 	case 37:
-#line 2710 "upb/json/parser.rl"
+#line 2701 "upb/json/parser.rl"
 	{ p--; {stack[top++] = cs; cs = 78;goto _again;} }
 	break;
 	case 38:
-#line 2715 "upb/json/parser.rl"
+#line 2706 "upb/json/parser.rl"
 	{
         if (is_wellknown_msg(parser, UPB_WELLKNOWN_ANY)) {
           start_any_member(parser, p);
@@ -3107,11 +3098,11 @@ _match:
       }
 	break;
 	case 39:
-#line 2722 "upb/json/parser.rl"
+#line 2713 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_membername(parser)); }
 	break;
 	case 40:
-#line 2725 "upb/json/parser.rl"
+#line 2716 "upb/json/parser.rl"
 	{
         if (is_wellknown_msg(parser, UPB_WELLKNOWN_ANY)) {
           end_any_member(parser, p);
@@ -3121,7 +3112,7 @@ _match:
       }
 	break;
 	case 41:
-#line 2736 "upb/json/parser.rl"
+#line 2727 "upb/json/parser.rl"
 	{
         if (is_wellknown_msg(parser, UPB_WELLKNOWN_ANY)) {
           start_any_object(parser, p);
@@ -3131,7 +3122,7 @@ _match:
       }
 	break;
 	case 42:
-#line 2745 "upb/json/parser.rl"
+#line 2736 "upb/json/parser.rl"
 	{
         if (is_wellknown_msg(parser, UPB_WELLKNOWN_ANY)) {
           CHECK_RETURN_TOP(end_any_object(parser, p));
@@ -3141,54 +3132,54 @@ _match:
       }
 	break;
 	case 43:
-#line 2757 "upb/json/parser.rl"
+#line 2748 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(start_array(parser)); }
 	break;
 	case 44:
-#line 2761 "upb/json/parser.rl"
+#line 2752 "upb/json/parser.rl"
 	{ end_array(parser); }
 	break;
 	case 45:
-#line 2766 "upb/json/parser.rl"
+#line 2757 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(start_number(parser, p)); }
 	break;
 	case 46:
-#line 2767 "upb/json/parser.rl"
+#line 2758 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_number(parser, p)); }
 	break;
 	case 47:
-#line 2769 "upb/json/parser.rl"
+#line 2760 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(start_stringval(parser)); }
 	break;
 	case 48:
-#line 2770 "upb/json/parser.rl"
+#line 2761 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_stringval(parser)); }
 	break;
 	case 49:
-#line 2772 "upb/json/parser.rl"
+#line 2763 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_bool(parser, true)); }
 	break;
 	case 50:
-#line 2774 "upb/json/parser.rl"
+#line 2765 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_bool(parser, false)); }
 	break;
 	case 51:
-#line 2776 "upb/json/parser.rl"
+#line 2767 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_null(parser)); }
 	break;
 	case 52:
-#line 2778 "upb/json/parser.rl"
+#line 2769 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(start_subobject_full(parser)); }
 	break;
 	case 53:
-#line 2779 "upb/json/parser.rl"
+#line 2770 "upb/json/parser.rl"
 	{ end_subobject_full(parser); }
 	break;
 	case 54:
-#line 2784 "upb/json/parser.rl"
+#line 2775 "upb/json/parser.rl"
 	{ p--; {cs = stack[--top]; goto _again;} }
 	break;
-#line 3192 "upb/json/parser.c"
+#line 3183 "upb/json/parser.c"
 		}
 	}
 
@@ -3205,32 +3196,32 @@ _again:
 	while ( __nacts-- > 0 ) {
 		switch ( *__acts++ ) {
 	case 0:
-#line 2593 "upb/json/parser.rl"
+#line 2584 "upb/json/parser.rl"
 	{ p--; {cs = stack[--top]; 	if ( p == pe )
 		goto _test_eof;
 goto _again;} }
 	break;
 	case 46:
-#line 2767 "upb/json/parser.rl"
+#line 2758 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_number(parser, p)); }
 	break;
 	case 49:
-#line 2772 "upb/json/parser.rl"
+#line 2763 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_bool(parser, true)); }
 	break;
 	case 50:
-#line 2774 "upb/json/parser.rl"
+#line 2765 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_bool(parser, false)); }
 	break;
 	case 51:
-#line 2776 "upb/json/parser.rl"
+#line 2767 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_null(parser)); }
 	break;
 	case 53:
-#line 2779 "upb/json/parser.rl"
+#line 2770 "upb/json/parser.rl"
 	{ end_subobject_full(parser); }
 	break;
-#line 3234 "upb/json/parser.c"
+#line 3225 "upb/json/parser.c"
 		}
 	}
 	}
@@ -3238,7 +3229,7 @@ goto _again;} }
 	_out: {}
 	}
 
-#line 2812 "upb/json/parser.rl"
+#line 2803 "upb/json/parser.rl"
 
   if (p != pe) {
     upb_status_seterrf(parser->status, "Parse error at '%.*s'\n", pe - p, p);
@@ -3281,13 +3272,13 @@ static void json_parser_reset(upb_json_parser *p) {
 
   /* Emit Ragel initialization of the parser. */
   
-#line 3285 "upb/json/parser.c"
+#line 3276 "upb/json/parser.c"
 	{
 	cs = json_start;
 	top = 0;
 	}
 
-#line 2854 "upb/json/parser.rl"
+#line 2845 "upb/json/parser.rl"
   p->current_state = cs;
   p->parser_top = top;
   accumulate_clear(p);
diff --git a/upb/json/parser.rl b/upb/json/parser.rl
index 0f58f84b18..eccd53039f 100644
--- a/upb/json/parser.rl
+++ b/upb/json/parser.rl
@@ -1694,24 +1694,15 @@ static void start_timestamp_zone(upb_json_parser *p, const char *ptr) {
   capture_begin(p, ptr);
 }
 
-static int div_round_up2(int n, int d) {
-  return (n + d - 1) / d;
-}
-
 /* epoch_days(1970, 1, 1) == 1970-01-01 == 0. */
 static int epoch_days(int year, int month, int day) {
   static const uint16_t month_yday[12] = {0,   31,  59,  90,  120, 151,
                                           181, 212, 243, 273, 304, 334};
-  int febs_since_0 = month > 2 ? year + 1 : year;
-  int leap_days_since_0 = div_round_up2(febs_since_0, 4) -
-                          div_round_up2(febs_since_0, 100) +
-                          div_round_up2(febs_since_0, 400);
-  int days_since_0 =
-      365 * year + month_yday[month - 1] + (day - 1) + leap_days_since_0;
-
-  /* Convert from 0-epoch (0001-01-01 BC) to Unix Epoch (1970-01-01 AD).
-   * Since the "BC" system does not have a year zero, 1 BC == year zero. */
-  return days_since_0 - 719528;
+  uint32_t year_adj = year + 4800;  /* Ensure positive year, multiple of 400. */
+  uint32_t febs = year_adj - (month <= 2 ? 1 : 0);  /* Februaries since base. */
+  uint32_t leap_days = 1 + (febs / 4) - (febs / 100) + (febs / 400);
+  uint32_t days = 365 * year_adj + leap_days + month_yday[month - 1] + day - 1;
+  return days - 2472692;  /* Adjust to Unix epoch. */
 }
 
 static int64_t upb_timegm(const struct tm *tp) {
diff --git a/upb/json_decode.c b/upb/json_decode.c
index 54a55ad135..bb4337c06b 100644
--- a/upb/json_decode.c
+++ b/upb/json_decode.c
@@ -979,18 +979,16 @@ static int jsondec_nanos(jsondec *d, const char **ptr, const char *end) {
   return nanos;
 }
 
-// jsondec_epochdays(1970, 1, 1) == 1970-01-01 == 0
-static int jsondec_epochdays(int y, int m, int d) {
-  unsigned year_base = 4800;  /* Before minimum year, divisible by 100 & 400 */
-  unsigned epoch = 2472632;   /* Days between year_base and 1970 (Unix epoch) */
-  unsigned carry = (unsigned)m - 3 > m;
-  unsigned m_adj = m - 3 + (carry ? 12 : 0);   /* Month, counting from March */
-  unsigned y_adj = y + year_base - carry;  /* Year, positive and March-based */
-  unsigned base_days = (365 * 4 + 1) * y_adj / 4;    /* Approx days for year */
-  unsigned centuries = y_adj / 100;
-  unsigned extra_leap_days = (3 * centuries + 3) / 4; /* base_days correction */
-  unsigned year_days = (367 * (m_adj + 1)) / 12 - 30;  /* Counting from March */
-  return base_days - extra_leap_days + year_days + (d - 1) - epoch;
+/* jsondec_epochdays(1970, 1, 1) == 1970-01-01 == 0. */
+int jsondec_epochdays(int y, int m, int d) {
+  const uint32_t year_base = 4800;    /* Before min year, multiple of 400. */
+  const uint32_t m_adj = m - 3;       /* March-based month. */
+  const uint32_t carry = m_adj > m ? 1 : 0;
+  const uint32_t adjust = carry ? 12 : 0;
+  const uint32_t y_adj = y + year_base - carry;
+  const uint32_t month_days = ((m_adj + adjust) * 62719 + 769) / 2048;
+  const uint32_t leap_days = y_adj / 4 - y_adj / 100 + y_adj / 400;
+  return y_adj * 365 + leap_days + month_days + (d - 1) - 2472632;
 }
 
 static int64_t jsondec_unixtime(int y, int m, int d, int h, int min, int s) {