3 files changed, 40 insertions, 5 deletions

diff --git a/tcp.c b/tcp.c
index bb661ee..026546a 100644
--- a/tcp.c
+++ b/tcp.c
@@ -788,11 +788,7 @@ static void tcp_get_sndbuf(struct tcp_tap_conn *conn)
 		return;
 	}
 
-	v = sndbuf;
-	if (v >= SNDBUF_BIG)
-		v /= 2;
-	else if (v > SNDBUF_SMALL)
-		v -= v * (v - SNDBUF_SMALL) / (SNDBUF_BIG - SNDBUF_SMALL) / 2;
+	v = clamped_scale(sndbuf, sndbuf, SNDBUF_SMALL, SNDBUF_BIG, 50);
 
 	SNDBUF_SET(conn, MIN(INT_MAX, v));
 }
diff --git a/util.c b/util.c
index f32c9cb..2232a24 100644
--- a/util.c
+++ b/util.c
@@ -1223,3 +1223,41 @@ void fsync_pcap_and_log(void)
 	if (log_file != -1)
 		(void)fsync(log_file);
 }
+
+/**
+ * clamped_scale() - Scale @x from 100% to f% depending on @y's value
+ * @x:		Value to scale
+ * @y:		Value determining scaling
+ * @lo:		Lower bound for @y (start of y-axis slope)
+ * @hi:		Upper bound for @y (end of y-axis slope)
+ * @f:		Scaling factor, percent (might be less or more than 100)
+ *
+ * Return: @x scaled by @f * linear interpolation of @y between @lo and @hi
+ *
+ * In pictures:
+ *
+ *                f % -> ,----   * If @y < lo (for example, @y is y0), return @x
+ *                      /|   |
+ *                     / |   |   * If @lo < @y < @hi (for example, @y is y1),
+ *                    /  |   |     return @x scaled by a factor linearly
+ * (100 + f) / 2 % ->/   |   |     interpolated between 100% and f% depending on
+ *                  /|   |   |     @y's position between @lo (100%) and @hi (f%)
+ *                 / |   |   |
+ *                /  |   |   |   * If @y > @hi (for example, @y is y2), return
+ * 100 % -> -----'   |   |   |     @x * @f / 100
+ *           |   |   |   |   |
+ *          y0  lo  y1  hi  y2   Example: @f = 150, @lo = 10, @hi = 20, @y = 15,
+ *                                        @x = 1000
+ *                                        -> interpolated factor is 125%
+ *                                        -> return 1250
+ */
+long clamped_scale(long x, long y, long lo, long hi, long f)
+{
+	if (y < lo)
+		return x;
+
+	if (y > hi)
+		return x * f / 100;
+
+	return x - (x * (y - lo) / (hi - lo)) * (100 - f) / 100;
+}
diff --git a/util.h b/util.h
index 17f5ae0..744880b 100644
--- a/util.h
+++ b/util.h
@@ -242,6 +242,7 @@ int read_remainder(int fd, const struct iovec *iov, size_t cnt, size_t skip);
 void close_open_files(int argc, char **argv);
 bool snprintf_check(char *str, size_t size, const char *format, ...);
 void fsync_pcap_and_log(void);
+long clamped_scale(long x, long y, long lo, long hi, long f);
 
 /**
  * af_name() - Return name of an address family