Simplify ring space calculations

It isn't necessary to branch here to avoid underflow.  Essentially, the way
that unsigned binary integers work "automatically" does what this code was
doing.

Note that these expressions only work for a ring buffer that, like this one,
has a power of 2 (real) size and a maximum capacity 1 less than that.

1 files changed, 2 insertions, 14 deletions

diff --git a/src/ring.c b/src/ring.c
index 4998112..9b6a69b 100644
--- a/src/ring.c
+++ b/src/ring.c
@@ -102,11 +102,7 @@ zix_ring_reset(ZixRing* ring)
 static inline uint32_t
 read_space_internal(const ZixRing* ring, uint32_t r, uint32_t w)
 {
-  if (r < w) {
-    return w - r;
-  }
-
-  return (w - r + ring->size) & ring->size_mask;
+  return (w - r) & ring->size_mask;
 }
 
 uint32_t
@@ -118,15 +114,7 @@ zix_ring_read_space(const ZixRing* ring)
 static inline uint32_t
 write_space_internal(const ZixRing* ring, uint32_t r, uint32_t w)
 {
-  if (r == w) {
-    return ring->size - 1;
-  }
-
-  if (r < w) {
-    return ((r - w + ring->size) & ring->size_mask) - 1;
-  }
-
-  return (r - w) - 1;
+  return (r - w - 1U) & ring->size_mask;
 }
 
 uint32_t