From c26aed40f4fd18f86bcc6aba557cab700b129b73 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Thu, 18 Nov 2010 22:04:46 +0000 Subject: [PATCH] filter: use reciprocal divide At compile time, we can replace the DIV_K instruction (divide by a constant value) by a reciprocal divide. At exec time, the expensive divide is replaced by a multiply, a less expensive operation on most processors. Signed-off-by: Eric Dumazet Acked-by: Changli Gao Signed-off-by: David S. Miller --- net/core/filter.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/net/core/filter.c b/net/core/filter.c index c0b68f7c8036..23e0a2a9a4de 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -37,6 +37,7 @@ #include #include #include +#include enum { BPF_S_RET_K = 1, @@ -205,7 +206,7 @@ unsigned int sk_run_filter(struct sk_buff *skb, const struct sock_filter *fentry A /= X; continue; case BPF_S_ALU_DIV_K: - A /= K; + A = reciprocal_divide(A, K); continue; case BPF_S_ALU_AND_X: A &= X; @@ -506,6 +507,7 @@ int sk_chk_filter(struct sock_filter *filter, int flen) /* check for division by zero */ if (ftest->k == 0) return -EINVAL; + ftest->k = reciprocal_value(ftest->k); break; case BPF_S_LD_MEM: case BPF_S_LDX_MEM: -- 2.30.2