Add a new notion of "stamps" to be a fast 32-bit monotonic timestamp

The goal here is to replace our use of msec-based timestamps with
something less precise, but easier to calculate.  We're doing this
because calculating lots of msec-based timestamps requires lots of
64/32 division operations, which can be inefficient on 32-bit
platforms.

We make sure that these stamps can be calculated using only the
coarse monotonic timer and 32-bit bitwise operations.

1 files changed, 3 insertions, 3 deletions

diff --git a/src/common/buffers.c b/src/common/buffers.c
index c45e13d551..e0ef0dc773 100644
--- a/src/common/buffers.c
+++ b/src/common/buffers.c
@@ -472,7 +472,7 @@ buf_add_chunk_with_capacity(buf_t *buf, size_t capacity, int capped)
     chunk = chunk_new_with_alloc_size(buf_preferred_chunk_size(capacity));
   }
 
-  chunk->inserted_time = (uint32_t)monotime_coarse_absolute_msec();
+  chunk->inserted_time = monotime_coarse_get_stamp();
 
   if (buf->tail) {
     tor_assert(buf->head);
@@ -487,8 +487,8 @@ buf_add_chunk_with_capacity(buf_t *buf, size_t capacity, int capped)
 }
 
 /** Return the age of the oldest chunk in the buffer <b>buf</b>, in
- * milliseconds.  Requires the current monotonic time, in truncated msec,
- * as its input <b>now</b>.
+ * timestamp units.  Requires the current monotonic timestamp as its
+ * input <b>now</b>.
  */
 uint32_t
 buf_get_oldest_chunk_timestamp(const buf_t *buf, uint32_t now)