[CCID 3]: Modulo-16 arithmetic for window counters
This implements modulo-16 arithmetic which is needed to compare
the 4-bit CCID 3 window counter (CCVal) values; it respects
circular wraparound and returns a-b mod 16.
Implemented as a macro, since required in several places.
Signed-off-by: Gerrit Renker <gerrit@xxxxxxxxxxxxxx>
---
net/dccp/ccids/ccid3.c | 4 +---
net/dccp/ccids/lib/packet_history.c | 4 +---
net/dccp/ccids/lib/packet_history.h | 3 ++-
3 files changed, 4 insertions(+), 7 deletions(-)
--- a/net/dccp/ccids/lib/packet_history.h
+++ b/net/dccp/ccids/lib/packet_history.h
@@ -47,7 +47,8 @@
#define TFRC_RECV_NUM_LATE_LOSS 3
#define TFRC_WIN_COUNT_PER_RTT 4
-#define TFRC_WIN_COUNT_LIMIT 16
+/* Subtraction a-b modulo-16, respects circular wrap-around */
+#define SUB16(a,b) (((a) + 16 - (b)) & 0xF)
/*
* Transmitter History data structures and declarations
--- a/net/dccp/ccids/ccid3.c
+++ b/net/dccp/ccids/ccid3.c
@@ -841,9 +841,7 @@ static u32 ccid3_hc_rx_calc_first_li(str
step = 1;
break;
case 1:
- interval = win_count - entry->dccphrx_ccval;
- if (interval < 0)
- interval += TFRC_WIN_COUNT_LIMIT;
+ interval = SUB16(win_count, entry->dccphrx_ccval);
if (interval > 4)
goto found;
break;
--- a/net/dccp/ccids/lib/packet_history.c
+++ b/net/dccp/ccids/lib/packet_history.c
@@ -291,9 +291,7 @@ void dccp_rx_hist_add_packet(struct dccp
win_count = entry->dccphrx_ccval;
break;
case 2:
- tmp = win_count - entry->dccphrx_ccval;
- if (tmp < 0)
- tmp += TFRC_WIN_COUNT_LIMIT;
+ tmp = SUB16(win_count, entry->dccphrx_ccval);
if (tmp > TFRC_WIN_COUNT_PER_RTT + 1) {
/*
* We have found a packet older
-
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