Simplify and comment the translation between
registers and struct tm.

Signed-off-by: Michael Davidsaver <mdavidsaver@gmail.com>
---
 hw/timer/ds1338.c | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/hw/timer/ds1338.c b/hw/timer/ds1338.c
index b56db5852e..637a0f4246 100644
--- a/hw/timer/ds1338.c
+++ b/hw/timer/ds1338.c
@@ -89,9 +89,13 @@ static void capture_current_time(DS1338State *s)
      */
     struct tm now;
     qemu_get_timedate(&now, s->offset);
+
     s->nvram[R_SEC] = to_bcd(now.tm_sec);
     s->nvram[R_MIN] = to_bcd(now.tm_min);
     if (ARRAY_FIELD_EX32(s->nvram, HOUR, SET12)) {
+        /* 12 hour mode.
+         * map 0-23 to 1-12 am/pm
+         */
         int tmp = now.tm_hour;
         if (tmp % 12 == 0) {
             tmp += 12;
@@ -101,7 +105,9 @@ static void capture_current_time(DS1338State *s)
         } else {
             s->nvram[R_HOUR] = R_HOUR_SET12_MASK | R_HOUR_AMPM_MASK | to_bcd(tmp - 12);
         }
+
     } else {
+        /* 24 hour mode. */
         s->nvram[R_HOUR] = to_bcd(now.tm_hour);
     }
     s->nvram[R_WDAY] = (now.tm_wday + s->wday_offset) % 7 + 1;
@@ -178,14 +184,13 @@ static int ds1338_send(I2CSlave *i2c, uint8_t data)
             break;
         case R_HOUR:
             if (FIELD_EX32(data, HOUR, SET12)) {
-                int tmp = from_bcd(FIELD_EX32(data, HOUR, HOUR12));
+                /* 12 hour (1-12) */
+                /* read and wrap 1-12 -> 0-11 */
+                now.tm_hour = from_bcd(FIELD_EX32(data, HOUR, HOUR12)) % 12u;
                 if (FIELD_EX32(data, HOUR, AMPM)) {
-                    tmp += 12;
+                    now.tm_hour += 12;
                 }
-                if (tmp % 12 == 0) {
-                    tmp -= 12;
-                }
-                now.tm_hour = tmp;
+
             } else {
                 now.tm_hour = from_bcd(FIELD_EX32(data, HOUR, HOUR24));
             }
-- 
2.11.0

On Thu, Jul 05, 2018 at 11:19:51AM -0700, Michael Davidsaver wrote:
> Simplify and comment the translation between
> registers and struct tm.
> 
> Signed-off-by: Michael Davidsaver <mdavidsaver@gmail.com>

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

although..

[snip]
> @@ -101,7 +105,9 @@ static void capture_current_time(DS1338State *s)
>          } else {
>              s->nvram[R_HOUR] = R_HOUR_SET12_MASK | R_HOUR_AMPM_MASK | to_bcd(tmp - 12);
>          }
> +
>      } else {

I'm not real fond of blank lines before the ends of blocks.

> +        /* 24 hour mode. */
>          s->nvram[R_HOUR] = to_bcd(now.tm_hour);
>      }
>      s->nvram[R_WDAY] = (now.tm_wday + s->wday_offset) % 7 + 1;
> @@ -178,14 +184,13 @@ static int ds1338_send(I2CSlave *i2c, uint8_t data)
>              break;
>          case R_HOUR:
>              if (FIELD_EX32(data, HOUR, SET12)) {
> -                int tmp = from_bcd(FIELD_EX32(data, HOUR, HOUR12));
> +                /* 12 hour (1-12) */
> +                /* read and wrap 1-12 -> 0-11 */
> +                now.tm_hour = from_bcd(FIELD_EX32(data, HOUR, HOUR12)) % 12u;
>                  if (FIELD_EX32(data, HOUR, AMPM)) {
> -                    tmp += 12;
> +                    now.tm_hour += 12;
>                  }
> -                if (tmp % 12 == 0) {
> -                    tmp -= 12;
> -                }
> -                now.tm_hour = tmp;
> +
>              } else {
>                  now.tm_hour = from_bcd(FIELD_EX32(data, HOUR, HOUR24));
>              }

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson