[PATCH v3 1/2] libuuid: Refactor UUID time conversion for pre-epoch dates

[Kiran Rangoon <kiranrangoon0@gmail.com>]

I revised the code in response to your feedback.

> Looking at this more closely: __uuid_time() is directly exposed to users
> of libuuid as uuid_time(). This means that any change of the function's
> contract would break all external users and should be avoided at all
> costs. 

Reversed the change there.

> Fortunately it turns out that the timestamps embedded in UUIDs
> only use 60 bits. This means that the calculation can be performed in an
> int64_t without any risk of over- or underflow. Please try to implement
> it that way instead. 

I'm using signed int64_t here as suggested.

> It might be useful to change the signature of gregorian_to_unix() to
> "static void gregorian_to_unix(uint64_t ts, struct timeval *tv)".

I revised the code to use a struct timeval now. 

> Also please perform each logical step in a dedicated commit.

I made two commits, one for the code change and the other for tests, but
if there is a way you would perfer me to do it I could change it.

---
 libuuid/src/uuid_time.c | 25 +++++++++----------------
 1 file changed, 9 insertions(+), 16 deletions(-)

diff --git a/libuuid/src/uuid_time.c b/libuuid/src/uuid_time.c
index f0d2c8f36..293fc7e68 100644
--- a/libuuid/src/uuid_time.c
+++ b/libuuid/src/uuid_time.c
@@ -60,34 +60,29 @@
 /* prototype to make compiler happy */
 time_t __uuid_time(const uuid_t uu, struct timeval *ret_tv);
 
-static int64_t gregorian_to_unix(uint64_t ts)
+static void gregorian_to_unix(uint64_t ts, struct timeval *tv)
 {
-    const uint64_t offset = 0x01B21DD213814000ULL;
+	const uint64_t offset = 0x01B21DD213814000ULL;
+	int64_t t = (int64_t) ts - (int64_t) offset;
 
-    if (ts < offset) {
-        errno = EOVERFLOW;
-        return -1;
-    }
-
-    return ts - offset;
+	tv->tv_sec = t / 10000000;
+	tv->tv_usec = (t % 10000000) / 10;
 }
 
 static void uuid_time_v1(const struct uuid *uuid, struct timeval *tv)
 {
 	uint32_t high;
-	int64_t clock_reg;
+	uint64_t clock_reg;
 
 	high = uuid->time_mid | ((uuid->time_hi_and_version & 0xFFF) << 16);
 	clock_reg = uuid->time_low | ((uint64_t) high << 32);
 
-	clock_reg = gregorian_to_unix(clock_reg);
-	tv->tv_sec = clock_reg / 10000000;
-	tv->tv_usec = (clock_reg % 10000000) / 10;
+	gregorian_to_unix(clock_reg, tv);
 }
 
 static void uuid_time_v6(const struct uuid *uuid, struct timeval *tv)
 {
-	int64_t clock_reg;
+	uint64_t clock_reg;
 
 	clock_reg = uuid->time_low;
 	clock_reg <<= 16;
@@ -95,9 +90,7 @@ static void uuid_time_v6(const struct uuid *uuid, struct timeval *tv)
 	clock_reg <<= 12;
 	clock_reg |= uuid->time_hi_and_version & 0xFFF;
 
-	clock_reg = gregorian_to_unix(clock_reg);
-	tv->tv_sec = clock_reg / 10000000;
-	tv->tv_usec = (clock_reg % 10000000) / 10;
+	gregorian_to_unix(clock_reg, tv);
 }
 
 static void uuid_time_v7(const struct uuid *uuid, struct timeval *tv)
-- 
2.47.3