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-rw-r--r--src/vnet/ip/ip_packet.h16
1 files changed, 15 insertions, 1 deletions
diff --git a/src/vnet/ip/ip_packet.h b/src/vnet/ip/ip_packet.h
index b0b5f41260c..d862caa3a52 100644
--- a/src/vnet/ip/ip_packet.h
+++ b/src/vnet/ip/ip_packet.h
@@ -301,6 +301,20 @@ always_inline u16
ip_csum_fold (ip_csum_t c)
{
/* Reduce to 16 bits. */
+#ifdef __x86_64__
+ u64 tmp;
+ asm volatile(
+ /* using ADC is much faster than mov, shift, add sequence
+ * compiler produces */
+ "mov %k[sum], %k[tmp] \n\t"
+ "shr $32, %[sum] \n\t"
+ "add %k[tmp], %k[sum] \n\t"
+ "mov $16, %k[tmp] \n\t"
+ "shrx %k[tmp], %k[sum], %k[tmp] \n\t"
+ "adc %w[tmp], %w[sum] \n\t"
+ "adc $0, %w[sum] \n\t"
+ : [ sum ] "+&r"(c), [ tmp ] "=&r"(tmp));
+#else
#if uword_bits == 64
c = (c & (ip_csum_t) 0xffffffff) + (c >> (ip_csum_t) 32);
c = (c & 0xffff) + (c >> 16);
@@ -308,7 +322,7 @@ ip_csum_fold (ip_csum_t c)
c = (c & 0xffff) + (c >> 16);
c = (c & 0xffff) + (c >> 16);
-
+#endif
return c;
}